Life Sciences Module 11 and 12 - 120939

LIFE SCIENCES
GRADE 11 AND 12
MODULE
Table of Contents
Environmental studies ................................................................................................... 14
Population and community ecology ........................................................................... 14
Population ecology ................................................................................................. 14
What affects the size of a population? ................................................................... 15
Learning activity 1 Population parameters ............................................................. 15
Limiting factors........................................................................................................... 17
2. Mark-recapture method ......................................................................................... 20
Learning activity 4 Estimation of population size .................................................... 21
Question 1 .............................................................................................................. 21
2. Predator-prey relationships .................................................................................... 27
Learning activity 8 Predation ..................................................................................... 30
Class discussion ........................................................................................................ 31
How food webs impact on populations ...................................................................... 32
Animals with a dominant breeding pair ...................................................................... 55
The human population has exploded ..................................................................... 68
Ecological footprint .................................................................................................... 71
Human need for land versus conservation ............................................................. 71
Class discussion .................................................................................................... 72
Human endocrine system.............................................................................................. 74
Chemical co-ordination .............................................................................................. 74
How do exo– and endocrine glands differ? ............................................................ 75
Endocrine glands in the body .................................................................................... 75
1. Hypothalamus .................................................................................................... 77
2. Pituitary gland .................................................................................................... 77
Learning activity 1 .................................................................................................. 80
3. Thyroid gland ..................................................................................................... 81
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Homeostatic control mechanism ............................................................................ 85
4. Pancreas ............................................................................................................ 85
How insulin lowers blood sugar levels.................................................................... 87
How glucagon increases blood glucose ................................................................. 90
Diabetes (Diabetes mellitus) .................................................................................. 90
5. Adrenal glands ................................................................................................... 93
6. Gonads (reproductive organs)............................................................................ 96
What are the functions of progesterone? ............................................................... 97
Use of hormones in sport ....................................................................................... 99
Erythropoietin (EPO) ............................................................................................ 100
2.2 Reproduction in flowering plants ........................................................................ 106
What is the similarity between asexual and sexual reproduction? ....................... 106
What are the differences between asexual and sexual reproduction? ................. 106
Learning activity 1 ................................................................................................ 108
What is the advantage of sexual reproduction? ................................................... 108
What are the disadvantages of sexual reproduction? .......................................... 109
How does sexual reproduction take place? .......................................................... 109
Angiosperm reproduction ..................................................................................... 112
Male and female parts of a flower ........................................................................ 113
What is the difference between pollination and fertilisation? Pollination .............. 114
How asexual/sexual reproduction historically has lead to improved food crops ... 116
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How can plant breeders use asexual reproduction and engineering techniques to
benefit food production and help solve the current food crisis? ........................... 119
Use of sexual reproduction to produce new and improved varieties of food crops
............................................................................................................................. 124
What is a polyploid plant? .................................................................................... 125
Importance of seeds as a food source ................................................................. 128
The use of growth regulators in modern agricultural practices ............................. 131
2.3 Reproductive animal strategies.......................................................................... 135
A. Courtship ......................................................................................................... 136
2. Complex strategies .......................................................................................... 136
B. External versus internal fertilisation ................................................................. 137
D. Amniotic egg .................................................................................................... 143
How effective for survival are the reproductive strategies of K-strategy and r-
strategy species? ................................................................................................. 151
Male reproductive organs ..................................................................................... 155
Female reproductive organs................................................................................. 160
Life at molecular, cellular and tissue level ................................................................... 215
DNA – the code of life .............................................................................................. 215
DNA double helix ................................................................................................. 217
DNA precipitating ................................................................................................. 224
Protein synthesis .................................................................................................. 231
DNA fingerprints ................................................................................................... 241
Chromosomes and meiosis ..................................................................................... 247
A genetic diagram to show monohybrid inheritance ............................................. 278
The sex chromosomes ......................................................................................... 284
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Evolution ..................................................................................................................... 322
Inheritance of acquired characteristics .................................................................... 326
Analogous wings of a bat and an insect ............................................................... 347
Macro-evolution.................................................................................................... 359
Cladogenesis ....................................................................................................... 360
Gradualism ........................................................................................................... 362
Punctuated equilibrium......................................................................................... 363
Natural variation....................................................................................................... 364
Darwin’s four important observations ................................................................... 365
Hominid Studies....................................................................................................... 411
Cladogram to show mt DNA relationships among humans .................................. 520
‘Out of Africa’ model ............................................................................................. 520
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What are the Life Sciences?
The term ‘Life Sciences’ indicates clearly the two ideas held together in this subject:
Life refers to all living things – from the most basic of molecules through to the
interactions of organisms with one another and their environments.
Science indicates it is necessary to use certain methods in our study of the

subject. The two broad aims of any science are to increase existing knowledge
and discover new things.
We approach this using careful methods that can be copied by others.

These include:
o % proposing hypotheses (the predicted outcome of an

investigation) and
o % carrying out investigations and experiments to test these

hypotheses.
Scientific knowledge changes over time as more is discovered and understood

about our world; as such, Life Sciences is a constantly growing subject.
Why choose Life Sciences as a subject?
First, to give you knowledge and skills that are helpful in everyday life, even
if you do not pursue Life Sciences after school.
Secondly, to expose you to the wide variety of sub-fields within the subject that
could encourage or interest you to pursue a career in the sciences.
If you choose to study Life Sciences at school you will be able to study any Life
Science specialisations after school - such as microbiology, genetics, environmental
studies or biotechnology.
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What skills will Life Sciences equip you with?
This subject will teach you important biological concepts, processes, systems and
theories, and provide you with the skills to think, read and write about them. Life
Sciences will:
% give you the ability to evaluate and discuss scientific issues and processes
% provide an awareness of the ways biotechnology and a knowledge of Life

Sciences have benefited humankind
% show you the ways in which humans have impacted negatively on the
environment and organisms within it, and show you how to be a
responsible citizen in terms of the environment and conservation
% build an appreciation of the unique contribution of South Africa to Life Sciences -

both the diversity of the unique biomes within Southern Africa and the
contributions of South Africans to the scientific landscape.
Life Sciences Strands for Grade 12
Everything you study this year will fit into one of these three broad strands.
These knowledge pathways grow over your three years of FET.
Within each knowledge strand, ideas should not be studied separately; rather seek
to discover the links between related topics so that you grow in your understanding
of the inter-connectedness of life. As you study each section or chapter, look for the
broad strokes that place it under one of these strands:
Knowledge Strand 1: Life at a Molecular, Cellular and Tissue Level
Knowledge Strand 2: Life Processes in Plants and Animals
Knowledge Strand 3: Diversity, Change and Continuity
The Purpose of studying Life Sciences
There are three broad purposes, which will expand as we continue:
Aim 1 - knowing the content (theory);
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Aim 2 - doing practical work and investigations;
Aim 3 - understanding the applications of Life Sciences in society - both present

society (indigenous and western) and within the context of history.
Aim 1: Knowing the content of Life Sciences
Learning content involves understanding and making meaning of scientific ideas,

and then connecting these ideas. Theory is not just recalling facts; it is being able
to select important ideas, use different sources to learn, and describe concepts,
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processes and theories important to Life Sciences.
Within this you will learn to write summaries, develop your own diagrams and
reorganise data you are given into something meaningful. Additionally, you will learn to
interpret the data you are working with and link it to theory you have studied.
Aim 2: Doing practical work and investigations
Life Science is a fascinating subject and one of the best ways to understand it is
for you to see it in action. Therefore, it is important for you to know how to do
practical investigations. Within this, you will learn many useful skills like how to
follow instructions in a safe manner and how to name, recognise and handle
laboratory equipment.
During a practical investigation it is important for you to be able to make

observations. There are many ways this can be done - by making drawings,
describing what you see, taking measurements, and comparing materials before and
after a certain treatment. After making these observations it is important for you to
be able to measure and record them in a useful way. From here you will interpret
your data - you will look for the value in what you gathered and discuss the changes,
trends, and applications of what you have shown.
Finally, you will learn how to design your own investigations and experiments.
An investigation is more straightforward; for example, it could involve observing
soil profiles or counting animal populations.
Planning an experiment would begin with identifying a problem, and then

hypothesising a solution. In planning, you would identify variables and consider ways
to control them, select apparatus and materials to assist you, and then plan an
experiment that could be repeated by someone else. It is also important to consider
ways of capturing and interpreting your data.
Aim 3: Understanding the history, importance and modern applications of Life

sciences
The third aim of Life Sciences is to show you that school science can be relevant
to your life and that studying provides enrichment to you, even if you do not pursue
it past school level.
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As you study you will be exposed to the history of science and indigenous
knowledge systems from other times and other cultures. As you learn a certain
section of work, you will be introduced to how that knowledge was developed by
various scientists across the ages as they pursued a deeper understanding of the
world around them.
Our search of knowledge is shaped by our world view. Therefore, an important

concept to be aware of is that modern science (and technology) and traditional,
indigenous knowledge systems will sometimes differ in their approach to science.
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These seemingly opposite views can be held together as both bring a
certain dynamic; they should not be seen as opposing forces.
Finally, there are many possible career fields branching out of Life Sciences and, as
you learn, some of these will be shown through examples. Different sections would
open up different careers choices- in the past (for example palaeontology), the
present (like horticulture, game ranch management and preservation) and the future
(such as biotechnology and genetic engineering).
A final word on using this textbook
The best way to use this textbook to increase your understanding and thereby
results would be as follows:
Remember, good learning begins in the classroom so always pay

careful attention as your teacher works through it with you
Take note of sections you do not understand and revisit them
Ask questions to make sure you understand
Consider the end-of-chapter summaries and build on them to create your own
point-form summary note
Practice re-sketching the given diagrams
Work through all the given questions and answers at the end of the chapter
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Give details about the module on this page:
 How it should be used

 Editions / Publisher details
 Any acknowledgements etc.
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Environmental studies
Population and community ecology

Population ecology
Ecology is the study of the interactions of organisms with their physical and
biological environments and how these determine the distribution and make up of
populations within an ecosystem.
Population ecology is concerned with fluctuations in the size of a population and

the factors, both physical and social that regulates these fluctuations.
Individuals live together in populations. Different populations together

make up a community. Communities together with the non-living things in
their surroundings make up an ecosystem. All the ecosystems on earth
make up the biosphere.
Make sure you understand the meaning of the following terms as they will
be used throughout this strand.
The biosphere is the part of the earth where living organisms are found.
An ecosystem is made up of groups of different species of organisms that

interact with each other and with the environment.
An organism is an individual form of life, such as a bacterium, protest,

fungus, plant or animal, composed of a single cell or a complex of cells that
are capable of growing and reproducing.
A community is a group of different species that inhabit and interact in a

particular area.
A species is a group of closely related organisms that are very similar to

each other and are usually capable of interbreeding and producing fertile
offspring.
An individual is a single organism capable of independent existence.
A population is a group of organisms of the same species that occupy

the same area and can breed freely with each other.
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In this unit we will be studying the demographics of populations, i.e., the
statistics such as the size, age distribution, growth rate, density etc. of
populations.
What affects the size of a population?

Population size is the total number of individuals in a population. It can increase
or decreases over time with a change in one or more of the following:
Natality – birth rate in animals or the production of seeds in plants
Mortality – death rate
Immigration – individuals move into a population and stay
Emigration – individuals leave a population and do not return
For humans the:
birth rate is the number of births per 1000 people in a year.
death rate is the number of deaths per 1000 people per year.
Populations will therefore:
grow when birth and immigration exceed death and emigration.
decline when death and emigration exceed birth and immigration.
remain stable when birth and immigration approximately equal death and emigration.
In a closed population, with no immigration or emigration, the only parameters

affecting any change in population numbers will be births or deaths, e.g. fish in a
small pond.
Learning activity 1 Population parameters

Complete the following diagram to show the dynamic parameters affecting
the growth of a population. (4)
Total [4]
How is the growth of a population regulated?
If a few individuals enter an unoccupied area where there is no shortage of

food or other resources and no predators, they will reproduce and the
number of individuals will increase exponentially.
exponential = increasing more and more rapidly
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As the numbers increase, more demands are made on the available
resources and this builds up environmental resistance which causes the
birth rate/immigration rate to decrease and the death rate/emigration rate to
increase.
environmental resistance = the total number of factors that stop a

population from reproducing at its maximum rate
Eventually a balance is reached and the population stabilizes at a

particular size or number. This number is the carrying capacity of the
ecosystem.
carrying capacity = the population density that the environment can support
The population fluctuates around the carrying capacity until the

environment changes again. Population size fluctuates seasonally and
annually depending on the resources available.
The population size in an ecosystem is self-regulating. All negative-

feedback mechanisms (see Endocrine System later) are examples of this
self-regulation.
Graph to show carrying capacity
Learning activity 2 Environmental resistance
The growth rate of an aerobic bacterium was measured by inoculating

(‘placing’) some cells into a sterile nutrient fluid kept at 25°C.
aerobic = needs oxygen

sterile = contains no bacteria
nutrient = food
The results are shown below:
Hours after inoculation 0 5 10 15 20 25 30 50
Number of living cells (millions per 1 cm3) 10 10 50 410 450 460 200 50
1.Plot the above results on graph paper. (4)
2.Which three factors in this investigation represent environmental

resistance? (3)
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3.Calculate the maximum rate of increase in cells per hour. (4)
4.How might the results have been different if the culture had been
maintained:
4.1at 150C instead of 250C? (3)
4.2in nitrogen instead of air? (3)
Total [17]
Limiting factors
The factors that help to regulate the growth of a population are known as limiting
factors.
Limiting factors may be:
Density independent factors that limit the growth of a population as a result of natural
factors and not because of the density or number of the organisms, eg
–physical factors, eg rainfall, temperature, humidity, acidity, salinity
–catastrophic events, eg floods, fire, drought, volcanic eruptions, tsunami,
earthquakes.
Density dependent factors that have a greater effect when the population density is
high. This is because, when organisms are more crowded, they:
–compete more for resources such as food, light, oxygen, water, space and shelter
–are more easily found by predators
–spread disease and parasites more readily.
These limiting factors collectively build up environmental resistance.
Stable and unstable populations
A stable population is one in which numbers decrease when its size exceeds the
carrying capacity but increase again when numbers fall below the carrying capacity,
i.e. one that fluctuates around the carrying capacity.
An unstable population develops if the population far exceeds the carrying capacity.
This results in the habitat:
deteriorating rapidly, which leads to a lowering of the carrying capacity
eventually not being able to support the population, which will decrease rapidly and
possibly become extinct.
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Habitat won.t be able to support the population
Effect of exceeding carrying capacity, ie an unstable population
Learning activity 3 Carrying capacity
The graph illustrates the change in a springbok population on a fully fenced farm in
the Northern Cape.
The farm originally had approximately 100 springbok. All predators had been
eliminated before counting began. At a certain stage a large pack of jackals entered
through a break in the fence, which was repaired soon afterwards. The effect of the
jackals on the springbok population was clearly visible.
1. Suggest three reasons why the growth from between the period 1960
and 1975 is as it is. (3)
2. Approximately how many springbok were on the farm in 1975? (1)
3. During which year did the jackals enter the fenced area? Give a
reason for your answer from the information supplied. (3)
4. Between 1980 and 1990 the springbok population increased again.

Mention a possible reason for this increase. (2)
5. Mention four other factors, besides the jackals, which could have
caused the decline in the springbok population between 1975 and
1980? (4)
6. What method was most probably used to determine the size of the
springbok population? (1)
7. Do you think the line representing the carrying capacity is accurate?

Give a reason for your answer. (3)
8. The population from 2005 appears to have stabilised. Suggest how

the farmer might be controlling the population. (2)
9. What do you notice about the growth form from 1945 to 1955 and
1995 to 2000? (1)
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Total [20]
How is population size estimated?
It is important to be able to measure the size of a population to see if it is

changing over time. The following are two methods for determining the size
of a population:
1. Direct method
2. Mark-recapture method
1. Direct methods
Direct methods involve counting every single individual in a population.

This is called a census. This method can only be used:
 for populations where organisms are large enough to be seen

 where the area in which the animals are being counted is not too
large.
Direct methods can be used for individuals that are:
 slow moving, e.g. snails, tortoises or

 stationary, e.g. plants or
 usually stay in fixed position, eg barnacles, mussels.
If the area is too large to count every individual at one time either:
 aerial photographs can be taken to show the whole area in which

the population occurs, e.g. penguins, seals or a species of a large
tree.
 helicopters can be used to count larger animals, e.g. elephant and
buffalo in game reserves.
For humans, census forms can be filled in, accounting for everyone in a
household on a particular day.
Note:
In South Africa there is a population census every five years to determine

how many people live in this country. Such a census was held in 2011.
2. Indirect methods
Indirect methods involve counting a sample number of the population and

then using simple calculations to estimate the total size of the population,
bv.:
19
1. Quadrat method
This method involves counting the number of individuals in small measured

areas (quadrats) and then using these numbers to calculate the population
size of the total area with the aid of the following formula:
Total population = (N)
N = numbers in sample x size of whole habitat size of quadrat
The purpose of using a quadrat is to enable comparable samples to be

obtained from areas of consistent size and shape.
Method:
 Measure the size of the total area.

 Use a wooden frame of known diameters (usually 0.5 m2 or 1 m2) as
a quadrat. The same quadrat size must be used for each sample.
 Quadrats should be distributed at random.
 Count the individuals in each quadrat. Several samples should be
taken and the number of individuals per quadrat calculated. This is
the ‘number in sample’ in the formula.
 Using the above formula, calculate the size of the population.
Why is random sampling important?
As the distribution of individuals may not be uniform throughout the area, it

is important to sample as quadrats of the total area as possible to achieve
a true reflection of the distribution. This is known as random sampling.
2. Mark-recapture method
In this method a known number of individuals is caught and marked and
then released. After a suitable time period another sample is captured and
the number of marked individuals counted.
A formula is used to calculate population size based on the principle that

the ratio of unmarked to marked individuals in a sample will be the same as
the ratio in the population as a whole.
This method is suitable for animals that are:
 mobile, e.g. butterflies, birds, antelope

 not easily visible, e.g. fish in a dam.
Method:
 Mark out a well-defined area.

 Capture as many individuals as possible and mark them, e.g. metal
tag on the ear or a spot of oil-based paint.
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 Release the marked individuals back into the environment.
 Allow them time to mix thoroughly with the unmarked individuals of
the same species.
 Recapture as many individuals as possible.
 Count the total number and count the number of those which have
been marked.
 Calculate the total population size by using the Petersen index as
below:
P=MxC R
P = estimated population
M = total number of marked animals
C = total number of animals caught in second sample
R = total number of marked animals in second sample, i.e. recaptured.
Sometimes different letters are used but the principle stays the same.
What precautions must be taken for a reliable result?
 Only a short time should pass between the first and second
sampling, so that no births and deaths can occur.
 Sampling should be repeated several times and an average
population calculated.
 The marking must not damage the individual or affect its movement
or behaviour.
 The marked animal must mix freely with the rest of the population
before a new sample is taken.
 No immigration or emigration is allowed, i.e. the population must be
closed.
Learning activity 4 Estimation of population size

Question 1
A gardener wanted to find out how many snails there were in his garden which
covered an area of 40 m2. Using a 0.5 m2 quadrat he randomly selected six sample
areas and counted the snails in each. The following numbers were counted:
Quadrat sample Number of snails
1 7
2 16
21
3 8
4 6
5 19
6 10
What is the average number of snails per quadrat? (1)
Calculate the estimated snail population of the garden? Show your calculations. (3)
How would the estimate have differed if only quadrats 2 and 5 were counted? (2)
What could the gardener have done to make the estimate more valid? (2)
[8]
Question 2
A farmer needed to know how many fish he had in his farm dam.
He caught 20 fish and marked them by clipping out a small section of their tail fins.
He then released them back into the dam.
A few days later he caught 30 fish, of which five had been marked.
Estimate the total number of fish in the farm dam, showing your calculations. Do this
by using the formula you learnt. (4)
What precautions should this farmer take when using this mark-recapture technique
to make sure that the results are as accurate as possible? (3x2 = 6)
Hint: Note the term ‘this farmer’ – relate your answer to his particular situation.
[10]
Total [18]
Learning activity 5 Demonstration: Mark-recapture method

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Aim
To demonstrate how the mark-recapture method works for estimating the size of a
population.
What is needed?
Each group to have a glass jar filled with about 400 large bean seeds (or any other
type of seed or even marbles) – these represent a population.
Any form of making a mark, eg koki pen/permanent marking pen/nail polish.
Procedure
Empty the beans onto the tray and, with eyes closed, select 60 beans.
Mark each bean and allow the mark to dry.
Return the beans to the jar and shake to mix them with the other beans.
Empty beans onto tray again and with eyes closed, select another 60 beans.
Count the number of marked beans.
Calculate the estimated size of the bean population by using the Petersen index.
Repeat this procedure several times.
Count the beans in the jar and compare the actual number with the estimated
number you calculated.
Learning activity 6 Case study
Aim: To test public opinion regarding the culling of elephants.
You are the Park Manager in charge of controlling the elephant population in the
Kruger National Park. Your brief is to:
Estimate the number of elephants in the park
Present a rationale for culling the elephants
Compile a public survey form to test public opinion about culling
Present the results of the survey in a pie graph.
Procedure
Describe how you would set about estimating the elephant population of the Kruger
National Park, using helicopters.
Once you have established the numbers and compared these with the carrying
capacity of elephants in the Park and assessed the damage they are doing to the
environment, present your rationale for culling the elephants.
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Compile a survey form, presenting all the alternatives such as presented in the new
management framework for the Kruger National Park. These include female
contraception and relocation of entire elephant families.
The removal of fences between the Kruger and parks in neighboring Mozambique
has helped with migration into less congested areas, but not soon enough, according
to some experts.
Get as many of your family, friends and the public to complete the survey.
Draw a pie graph showing the results of the survey.
What an extended project this was. Did you manage to complete all the
different components? Well done if you did!
Learning activity 7 Short questions
1. Multiple choice
Various possible answers are given for the following questions. Choose the correct
alternative and write it below the relevant number in the table.
1 2 3 4 5 6 7
Which fact is not true of a population? A population consists of a group of organisms:

(a) of the same species; (b) that live in a variety of areas; (c) that breed freely
amongst themselves; (d) that live in a defined area.
Which of the following collection of organisms represents a population? (a) bees,

frogs, crocodiles; (b) pea plants, grasshoppers, birds; (c) aphids, ladybirds, flies; (d)
bees in a hive.
Natality: (a) in plants, is the production of flowers; (b) in animals, is their birth rate; (c)
is the average number of offspring each female produces in a lifetime; (d) is a
population parameter that causes populations to decrease.
Environmental resistance: (a) prevents a new population from immigrating into a new
habitat; (b) causes the development of resistant strains of population under different
conditions; (c) is the sum of the factors inhibiting population growth; (d) ensures the
survival of the fittest.
Which line on the following graph indicates the carrying capacity of this habitat for
this particular population of animals?
24
Direct methods to estimate population size can be used for individuals that are: (a)
slow moving; (b) usually stay in fixed position; (c) stationary; (d) all the above.
The following are precautions taken to produce a reliable mark-recapture sampling

method, except (a) Only a short time should pass between the first and second
sampling. (b) Sampling should be repeated several times. (c) The marked animal
must not mix freely with the rest of the population before a new sample is taken. (d)
The marking must not damage the individual.
[7]
2. True or False
Write down if the following statements are true or false. If false, fill in the incorrect
word, followed by the correct word.
1.Excluding immigration and emigration and provided natality

exceeds mortality, a population will grow.
2.Direct sampling method can be applied to animals that are mobile.
3.At high population densities, food supplies diminish and toxic

waste decreases, both of which will cause a slower population
growth.
4.If the population size far exceeds the carrying capacity the habitat
will become degraded.
5.Mark-recapture sampling method is used to estimate the

population size of animals that are not easily visible.
6.Immigration is when individuals leave a population and do not

return.
[9]
3. Environmental terms
Give the correct term for each of the following.
1.The study of the interactions between groups of different species

and their environment within an ecosystem.
2.A population, the size of which fluctuates around the carrying
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capacity.
3.A group of individuals of the same species occupying a particular

space at a particular time.
4.A build up of limiting factors.
5.The movement of individuals out of an area.
6.The maximum number of individuals of a specific species that a

habitat can support.
7.Factors that produce environmental resistance as the density of a

population increases.
8.A study of the fluctuations in population size and the factors that
regulate them.
9.Sampling many different quadrats in a designated area.
10.A species with no living members.
[10]
4. Mix and match
Choose a concept from column B to match the word or term in column A, and write
down the correct letter next to the relevant number.
Column A Column B
natality
carrying capacity
mark and recapture
environmental resistance
exponential growth
A.A method to determine the size of a population without counting the whole
population
B.Maximum number of individuals of a species that the environment can support
C.Rapid increase in population size
D.Production of seeds
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E.Factors that stop a population from reproducing at its maximum rate
[5]
1 2 3 4 5
Total [31]
2. Predator-prey relationships
All living organisms within an ecosystem are interdependent. Changes in the
population size of one species can drastically affect that of another. This is shown
particularly clearly by the relationship between predator and prey populations.
Predation is a biological interaction where one species, the predator, kills and eats
another species, the prey. Predator and prey evolve together and are part of the
same environment.
The role that predators play in their environment actually helps to create and
maintain greater diversity within an ecosystem.
Predators do this by:
regulating the abundance and distribution of prey species. As the predator

population increases, the prey population decreases.
increasing the biodiversity of communities by preventing a single species from

becoming dominant.
keeping the prey population genetically fit by removing sick, injured and weak
individuals.
providing vital food sources for scavengers.
The feeding relationship between the predator and the prey determines the size of
the two populations by means of a negative feedback mechanism.
How does this relationship work?
As the prey population decreases due to predator killing, the food available for the
predators is less, and so their numbers subsequently decline.
With the predator pressure reduced, the numbers of the prey can increase once
again and the cycle goes on.
The result is a cyclical rising and falling of the numbers of the prey population, with a
slightly later cyclical pattern of the predator. See the graph below.
27
These fluctuations may occur seasonally or over a number of years.
Examples
Aphid-ladybird
Lion-zebra
Shark-fish.
1. Aphid– ladybird
Aphids are insects that suck the sap of many different plants, including crops. They
are therefore parasitic pests. Several species of ladybirds feed on aphids. They
are, therefore predators and the aphids are the prey.
A ladybird feeding on aphids
Batches of bright yellow eggs are laid amongst aphid colonies by the female
ladybirds. The adults feed on the aphids and as the larvae that hatch from the eggs,
get larger, they will also eat the aphids, reducing their population. This reduces the
food supply of the ladybirds and their population begins to decrease. The aphid
population can then recover and increase in number. In this way the two populations
fluctuate up and down.
28
Note:
Many insecticides will kill ladybirds as well as insect pests, so avoid their use.
2. Lion-zebra
Lions, the predators and zebras, the prey, depend on each other for their survival.
Both predator and prey evolve adaptations to outwit the other. In the case of the
lion/zebra relationship, the adaptation is speed of movement.
The fastest lions are able to catch and eat their prey more easily than slower lions,
so they survive and reproduce. Gradually, faster lions make up more of the
population.
The fastest zebras are able to escape the lions, so they survive and reproduce, and
gradually, faster zebras make up more of the population.
Note that as both organisms become faster to adapt to their environments, their
relationship remains the same: because they are both getting faster, neither gets
faster in relation to the other.
But the predator-prey relationship will be advantageous for the fitness of both
species when they compete against other species in the same ecosystem. As a
whole, one organism changes because of the other in a given environment, thus
displaying the signs of co-evolution.
Because lions are the predators for many species, zebras included, the populations
of these species would dramatically increase if lions became extinct. Conversely, if
zebras were to become extinct, the effect on lions would not be as detrimental
because, although zebras make up a high proportion of a lion's diet, lions have a
large range of prey so they still have many other sources of food.
29
3. Shark – fish
Sharks are at the top of the food chain in virtually every part of every ocean. In their
role of predator, they keep populations of other fish (and other marine organisms)
healthy and in balance in the ecosystem.
A shark as predator
How do sharks keep the oceans healthy?
Sharks tend to eat very efficiently, going after the old, the sick or slower fish in a
population that they prey upon. By removing the sick and weak they:
prevent the spread of disease
strengthen the gene pools of the prey species.
Since the largest, strongest and healthiest fish generally reproduce in greater
numbers, the outcome is larger numbers of healthier fish.
By preying on fish populations, sharks prevent them from increasing too rapidly and
becoming too dominant and upsetting the balance in the ecosystem.
Learning activity 8 Predation

Question 1
The following graph shows the variations in two populations of animals, bat-eared
fox and grasshoppers, in a very large area over a period of 80 years.
By writing down the sentences, using the correct word from between each bracket,
many observations and conclusions can be drawn from looking at the above graph.
Underline the correct words.
There will always be (one/two) wavy lines, one indicating prey population and one
predator population.
30
The line that peaks first and is higher is always the (prey/predator).
The peaks of predator and prey population density (don’t/do) overlap.
Predators can only survive if the number of prey (is less than/exceeds) the number
of predators.
An (increase/decrease) in number of predators results in number of prey decreasing.
With a decline of predators there is an (increase/ decrease) in prey.
[6]
Question 2
Mention three requirements that a group of organisms must satisfy before it can be
called a population. (3) They are not mentioned here – a bit of revision!
What type of interaction between the lynx and the rabbit is illustrated by the graph
above? (1)
The population fluctuations of these two animals go in cycles. Is the cycle 5, 10, 15
or 20 years? (1)
How many rabbits were there in 1950? (1)
How many lynxes were there in 1950? (1)
What happened to the rabbit population as the number of lynxes increased from
1945 to 1950? Explain your answer. (1 + 2)
What happened to the rabbit population after 1952/3? Suggest a possible reason for
this change. (1 + 3)
At some stage the lynx population graph line shows an uncharacteristic predator
shape in relationship to the grasshopper population. Approximately what period was
this? Suggest what might have caused this, supporting your answer with information
from the graph. (5)
[19]
Question 3
In your own words, explain how both lions and sharks help to increase the health of
their prey populations. (5)
Total [30]
Class discussion
31
Can the hunting and killing of whales and rhinoceros by humans be
regarded as predation? Think about this question and explain your ideas in
a class discussion.
How food webs impact on populations

A food web is an interconnected set of all the food chains in an
ecosystem.
Multiple food webs are made up of carnivores, herbivores, producers,

scavengers and decomposers that all help to keep ecosystems healthy and
balanced. To achieve this, the populations of species that make up a food
web must be kept in balance.
The removal of one species from a food web may have a large impact on
the populations of many of the other species.
An example of a food web
Although the web looks complex, it is just several food chains joined
together.
 grass → insect → vole → hawk

 grass → insect → frog → jackal
 grass → insect → vole → jackal
Slugs, rabbits and insects all eat grass, so, if the population of slugs is
decreased:
32
 There would be more grass for the rabbits and insects, so their
populations would increase.
 However, the thrushes would have to eat more insects to maintain
their population, so it is also possible that the population of insects
could decrease.
 This turn may reduce the populations of voles and frogs.
The disruption is even worse if the top predators, such as lions and
sharks, are removed from a food web. Their prey populations would rapidly
increase. For example, the loss of lions, leopards, wild dogs and hyenas in
parts of Africa, have allowed baboons to increase in number which has
created other sets of problems.
Note:
Human activities like pollution, habitat destruction, over-fishing and hunting

are largely to blame for the reduction of top predators.
3. Competition
When resources such as light, space, water, food or shelter become

limited, individuals have to compete with each other to survive.
competition = when two or more individuals compete for the same

resources that are in short supply
Competition can be a powerful force affecting the growth, distribution and

size of populations in nature.
A. Intraspecific competition
Intraspecific competition occurs between individualsof the same

species. This type of competition includescompetition for matesas well as
for the resources mentioned above.
This type of competition is the most intense as members of the same

species have similar habitats and resource requirements, eg tadpoles
competing for food in a pond.
Tadpoles competing for food
B. Interspecific competition
Interspecific competition occurs between individuals of different

species where the niches in a habitat are very similar, eg tadpoles and
small fish competing for food in a pond.
33
Learning activity 9 Competition
Four plant pots of the same size labelled A, B, C and D were each filled
with the same amount of soil. Seeds were planted in each of the pots as
follows:
Pot A – 2 pea seeds and 2 bean seeds

Pot B – 4 pea seeds and 6 bean seeds
Pot C – 8 pea seeds and 8 bean seeds
Pot D – 20 bean seeds
The pots were watered well and left in a sheltered area. After two weeks
the number of seedlings in each pot was counted. The average height of
the seedlings was noted. The results are as follows:
Number of plants Average height of plants (cm)
Pot A 4 6
Pot B 8 5
Pot C 8 3
Pot D 8 2
1.In which pot (A, B, C or D) will:
1.1the least competition occur? _____
1.2intraspecific competition occur? _____
1.3interspecific competition be the greatest? ___
1.4the growth be the least? _____
1.5there be a single population? _____ (5)
2.What is the carrying capacity of the pots? (1)
3.List three density dependent factors that may have regulated the number
of plants in pot D. (3)
4.Explain each of the following:
34
4.1a density-independent factor (3)
4.2predation. (2)
Total [14]
Ecological niches
For a population to survive, its individuals must survive and reproduce. To

do this they must:
 tolerate the physical environment (temperature, pH)

 obtain energy and nutrients
 cope with competition
 avoid predators.
These requirements form the ecological niche of the individuals.
ecological niche = all the conditions necessary for an organism to survive

and reproduce
You cannot study ecology without understanding what is meant by a

niche!
When two species with the same or similar ecological niches occupy the
same habitat, their ecological niches will overlap to a greater or lesser
extent. This can result in specialisation among closely related species,
eg Galapagos finches evolved a large variety of beak shapes and sizes to
suit their own type of food, creating their own ecological niches to prevent
competition. See pg. 247
specialisation = the structural and behavioural adaptations that enable

individuals of different species to co-exist.
The competition that arises from overlapping ecological niches can also
lead to one of two possible outcomes: competitive exclusion or competitive
coexistence.
Competitive exclusion
Competitive exclusion occurs when one of the two competing species is

much more successful than the other. The successful species survives and
the other disappears. This can result in extinction and it plays an important
role in the process of evolution, e.g. monkeys out-competed lemurs in
Africa. Lemurs are now found only on the island of Madagascar which was
once part of Africa, but split away from the continent millions of years ago
as a result of continental drift.
35
Competitive co-existence
Competitive co-existence arises when two competing species co-exist in

the same habitat. Although they have overlapping niches, and therefore
compete for the same resources, they are able to co-exist because they
use the resources slightly differently. This is called resource partitioning.
Resource partitioning
Resource partitioning is the evolutionary process whereby species with

similar requirements, living in the same habitat, evolve specialised
traits that enable them to utilise the resources differently, creating separate
niches to reduce interspecific competition and make co-existence possible.
The great diversity of species on earth is partly due to resource partitioning.
How can resources be partitioned?
Two species can eliminate competition for the same resource by using the
resource:
 at different times, e.g. one species of mouse feeds on insects

during the day and a second species feeds on the same insects at
night.
 in different parts of a habitat, e.g. different species of fish feeding
on the same resource but at different depths in a lake.
 in different parts of the same plant, e.g giraffe feeding on the upper
leaves of a tree and kudu feeding on the lower leaves of the same
tree.
A. Strategy among plants Resource partitioning in a forest
Indigenous forests are complex communities made up of many different

trees and other plants of varying size and species, creating a vertical
structure that divides the vegetation into layers. This pattern is
called stratification. The conditions at the uppermost layer, such as light
intensity, wind speed and humidity are quite different from those at the
forest floor.
A forest ecosystem is made up of:
 Tall trees such as yellow woods and stinkwoods create a high

upper canopy and are exposed to maximum light intensity.
 Shorter trees, such as bladdernuts and forest spoonwoods create
the understory of a forest and are exposed to less light intensity.
36
 Pioneer species and young trees such as Cape-beech and wild-
peach are found growing in the gaps between the trees.
 Epiphytes (lichens, mistletoe and orchids) that grow on tree trunks
and climbers (cat-thorn, forest grape) that twine around the
branches.
 Herbaceous ground layer thatis made up of various ferns and
shade-loving plants such as some sedges, grasses and dicotyledons.
Resource partitioning of light
The intensity of light diminishes as the rays pass through the different
layers of forest vegetation. Different species of plants have created
different niches by stratification. The different layers of vegetation are
adapted to photosynthesise in different light intensities, i.e. the resource,
light, is partitioned.
Strategies among animals
1. Coexisting large herbivores in African savannah
Both giraffe and kudu are browsers in woodland savannah areas.
The giraffe, with its elongated neck and legs, has its whole body well
adapted for browsing on leaves on the higher branches of trees. Giraffes
feed on many species, eg Acacia tortillis (umbrella acacia). They have a
tongue and lips that are tough to withstand the vicious thorns of these
plants. In this way they obtain their food beyond the reach of the other
hoofed animals that live in the same habitat.
A giraffe
Kudu are purely browsers and not known to eat grass. They utililise a
wider range of trees than any other antelope, preferring young shoots and
leaves but they will also eat seedpods of trees such as Terminalia species.
Kudu browsing on Terminalia spp
Kudu share many of their preferred species with giraffe such

as Combretum (bush willow) and all acacias especially A.
nigrescens (Kudu-thorn acacia) but competition has been eliminated
because they browse on the lower branches and giraffe on the upper
branches. In this way the resource (leaves – food) is partitioned.
37
There is still confusion regarding the naming of Acacias – these are
the original names.
2. Coexisting shorebirds
In a mixed community of shorebirds, different species can coexist and

make efficient use of the available space and food without excessive
competition because of differences in:
 feeding habits
 morphology
Feeding habits
Although huge flocks of different shorebirds may be found in one location,

they practise resource partitioning by dividing up the territory both
horizontally and vertically.
Horizontal division
Different species may feed:
 above the tide line

 follow the waterline of waves
 in the shallows
 on rocky outcrops
 in deeper water (those with longer legs).
Vertical division
Different species may:
 pick titbits off the ground

 probe underground
 prey on creatures living deeper in the water
 feed on titbits floating on the water surface.
‘Pickers’ or ‘probers’?
Shorebirds are divided into ‘pickers’ or ‘probers’ which prevents them from
competing for the same food.
 ‘Pickers’ search for food by sight and forage in a typical run-and-

peck manner. They run a certain distance with their heads held high,
then stop abruptly and peck at a morsel of food, eg White-fronted
sandplover.
 ‘Probers’ usually have long bills and they stick these into the soft
mud or sand to feel for prey, eg the Sandpiper's bill tip is mobile and
can act as a finger tip to grasp or grip prey of insect larvae or small
worms.
38
A sandpiper
Morphological adaptations
Shorebirds have different length bills and legs which enable them to feed
on different types of food.
 Oystercatchers have a triangular bill that is a cross between a knife

and a chisel. They may use their bills to either stab into an open
bivalve and severe the muscles that close the shells or to smash
open the shell.
 Shorebirds with upturned bills use it to ‘scythe’ the water, sweeping it
back and forth to stir up and snag prey, e.g. Avocet.
 Waders have long, slender legs for wading into the water to feed on
molluscs, crustaceans and small fish, eg Bar-tailed Godwit
An oystercatcher
Coexisting predators, e.g. lions and leopards
Many ecosystems have multiple predator species that not only compete for
shared prey, but also pose direct threats to each other. Both leopards and
lions are opportunistic, skilled hunters that stalk their prey. They can co-
exist, however, by resource partitioning in the following ways.
Co-existing predators:
 avoid competition by hunting at different times of the day.

Leopards are mainly nocturnal but will hunt during the day when
camouflaged by dense foliage in forests. Lions tend to hunt in the
early morning or at night.
 hunt different types of prey, eg lions prey mainly on medium sized
mammals such as wildebeest, zebras and warthogs, whereas
leopards prey mainly on smaller prey such as a variety antelopes
(eg impala) and smaller monkeys. They therefore co-exist by dietary
niche separation.
 hunt in different areas of the habitat.
Lions have the advantage of being larger and heavier than leopards which
they tend to dominate. Leopards however are faster than lions and are able
to subsist much better on small prey than lions. Leopards have the added
advantage of being able to climb trees with their kill. This keeps their prey
safe from wandering lions.
39
Learning activity 10 Resource partitioning
1.Read through the description of the stratification of a forest. In the table,

fill in the letters from the diagram that correspond to each layer, giving an
example of one plant you would expect to find in each layer. (12)
Layers Letters Examples
pioneers
epiphytes
canopy
climbers
understory
herbaceous plants
[12]
2.What effects will the canopy layer of a forest have on the light intensity
penetrating the forest? (2)
3.Mention two species of trees that are browsed by both giraffe and kudu
and explain how competition for food has been reduced. (2+2)
4.In your own words explain what is meant by horizontal division in

resource partitioning of shorebirds. Give examples where possible. (4)
5.In your own words explain what is meant by dietary niche separation with
regard to lions and leopards co-existing. (3)
Total [25]
40
1. Multiple choice
Various possible answers are given for the following questions. Choose the
correct alternative and write it below the relevant number in the table
below.
1 2 3 4 5 6 7
1. Which of the following statements is not true about the relationship

between predator and prey? (a) There is interspecific competition. (b)
Increased number of predators causes a decreased number of prey.
(c) Decreased number of predators causes an increased prey
number. (d) The prey usually decreases before the predators.
2. What feature does not relate to intraspecific competition? (a) It
occurs between individuals of the same species. (b) Only the fittest
will survive. (c) It occurs between individuals of different species. (d)
Competitors have similar habitats and resource requirements.
3. The energy available at each trophic level in a food chain affects
predator-prey relationships. The relationship between the rabbit and
jackal is shown on the following graph.
On which axis would you read off the number of animals shown on
line A on the graph? (a) Y1; (b) Time in months; (c) Y2; (d) Y1.
4. The relationship between fleas and a dog is most similar to the

relationship between: (a) honey bees and a flower; (b) orchids and a
tree; (c) nitrogen-fixing bacteria and a legume; (d) athlete's foot
fungus and a human.
5. The diagram shows a kelp forest food web. Which two groups of
organisms would most likely be competitors? (a) F and C and B and
C; (b) B and C and E and D; (c) B and E and A and B; (d) B and C
and E and F.
6. Although three different bird species all inhabit the same type of tree
in an area, competition between the birds rarely occurs. The most
likely explanation for this is that these birds: (a) share food with each
other; (b) have different ecological niches; (c) have a limited supply
of food; (d) are unable to interbreed.
7. The diagram represents a tree with three different species of warbler
in it, A, B and C. Each species occupies a different niche. A fourth
41
species, D, which has the same environmental requirements as
species B, enters the tree at point X.
Members of species D will most likely: (a) live in harmony with

species B; (b) move to a different level and live with species A or
species C; (c) stay at the entry level but change their diet;
(d) compete with species B.
[7]
2. Terms
Give the correct term / word for the following descriptions.
1.Individuals of one species that catch and eat another species.
2.An interconnected set of all the food chains in an ecosystem.
3.Two or more individuals of different species competing for the same

resources.
4.The structural and behavioural adaptations that enable individuals to co-

exist.
5.A process whereby species with similar requirements, living in the same
habitat, divide up resources so that different niches are created.
6.When one of the two competing species is much more successful than
the other.
7.Dividing vegetation into vertical layers.
8.All the conditions that are necessary for the survival of an organism.
9.A population where the size of that population fluctuates around the
carrying capacity.
10.A study of the fluctuations in population size and the factors that
regulate them.
11.The maximum number of individuals of a specific species that a habitat

can support.
12.Factors that produce environmental resistance as the density of a

population increases.
[12]
3. True and False
Write down if the following statements are either true or false. If the
statement is false, fill in the incorrect word followed by the correct one.
42
1.In a predator-prey graph the number of predators is less than the number
of prey.
2.The use of the same resources by two or more organisms is known as

predation.
3.The lions-zebra relationship is an example of resource portioning.
4.Competitive exclusion is the process where species evolve differences in

what they eat or where they feed in order to reduce competition.
5.If the population size far exceeds the carrying capacity the habitat will
become degraded.
6.Factors that prevent the growth of a population are collectively called

carrying capacity.
[10]
Total [29]
4. Ecological succession
Ecological succession is a predictable pattern of gradual change over
time in the types of species in a community following a disturbance.
Just a reminder … a biological community consists of all the

populations of different species that live together in the same area.
What are the types of succession?
There are two basic types of succession.
 Primary succession begins on sites that have not previously had

plants growing on them, such as beaches, larva flows, severe
landslips, ponds and bare rock.
 Secondary succession begins in areas where
a disturbance removes some or all species but the soil remains.
What determines community structure?
Community structure is not static; it is determined over timebysuccession

that takes place as a result of either or both of the following.
1.Disturbances, which are caused by:
 physical disasters, eg storms, floods, fires

 humans or animals, eg abandoned crop field, overgrazed area or
logged forest
 climate change.
43
Disturbance from logging
Disturbances create opportunities for new species to move in. The new
species will alter the character of the community, creating an environment
suitable to even newer species.
2.Competitive interactions between the organisms in a community, eg

competition, predation, etc. These have been discussed earlier.
Stages in succession
The order of change during succession is not random. Communities

initially have a small number of simple species which are gradually
replaced by a large number of complex species.
There are three stages of ecological succession:
1. Pioneer species stage
The bare ground conditions favour pioneer (early successional) plant

species. These species grow best where there is little competition for space
and resources.
Features of pioneer species
Pioneer species:
 are hardy as they must be able to withstand extreme variations in

temperature and moisture.
 establish rapidly although they are often slow growing, e.g. lichens.
 have spores or seeds that can disperse over long distances, e.g. tiny
seeds with ‘parachutes’.
 do not grow in shade, e.g. grass.
Pioneer species prepare the surroundings for later colonists by altering the
biotic and abiotic environment. biotic = living; abiotic = non-living
 Pioneer species build-up, stabilise and enrich the soil.

 Pioneer species alter the amount of light available by providing
shade.
These changes allow other species that are better suited to this modified
habitat to replace the pioneer species, which then disappear.
Primary succession
The following are the floral pioneer species. Lichens are the first species
to become established on rock after a disturbance. They do not need soil to
44
survive. Soil starts to form as lichens and physical weathering break down
rocks into smaller pieces. When lichens die, they decompose, adding small
amounts of organic matter to the newly formed soil.
Lichens on a new rock surface
Mosses and other simple plants follow.
Ferns, grasses and annuals arrive as the soil layer thickens.
The faunal pioneer species are initially mites, ants and spiders. Small
herbivores (insects, rodents and small birds) and other decomposers such
as earthworms and larvae move in when more food is available.
Secondary succession
The following are pioneer species of a secondary succession:
 Annuals (herbs and weeds)are the first species to appear after a disturbance.
 A year or so later grasses and perennials appear.
 In forest gaps or wetter sites a tangle of climbers develops.
2. Intermediate species stage

Ecological conditions change because:
 the soil can hold more water and is also more fertile.
 temperatures are less extreme as there is more shade.
As a result, a greater variety and number of organisms are able to move in.
 As the soil builds up, small non-woody herbaceous species give way to small
hardy woody plant species and these in turn to larger woody shrubs and
bushes(small trees)that are much slower growing. Grasses remain part of the
community. At a later stage some species can grow in the shade.
 Larger herbivores (hares, small antelope), small carnivores (caracal, wild
cats), snakes and raptors also become part of the community.
The intermediate species make the communities more structurally complex.
Caracal
3. Climax community
This is the last semi-stable stage or the endpoint of succession. Climax
communities vary, e.g. they could be large trees as in a forest biome, or grasses and
45
Acacia trees as in the Savannah biome, or dwarf, succulent shrubs as in the
Succulent Karoo biome.
Succulent Karoo
Savannah
You studied the various biomes in Grade 10 so will be familiar with the
components of other endpoints.
The animal species in the climax community are the most diverse and include the
large herbivores and carnivores.
It is important to realise that everything is in a state of transition. Future

disturbances can cause the species of a community to change. For example, a
higher rainfall could change the Succulent Karoo into a grassland; hence the term
semi-stable.
All over the world humans are destroying these climax communities. As a result they
are becoming increasingly rare as they take so long to develop.
What factors determine an endpoint to a community?
Any community – pioneer, successional or climax community can change.
These changes can be caused by environmental fluctuations such as:
1. Rainfall
The amount of rain is the most important factor determining successional

endpoints. For example, if the rainfall is more than 1 200 mm/year, the endpoint will
be a forest community. If there is a prolonged drought, species that are able to
withstand drier conditions will start dominating and change the character of the forest
community into a grassland or savannah endpoint.
2. Overgrazing
Overgrazing can change a community. For example:
 sheep in the Karoo are known to only select grasses, palatable herbs and
small shrubs.
 The un-eaten, unpalatable species then become dominant, forming the
endpoint.
 grazers often choose one grass species, which changes the composition of
the climax communities in the grassland biome. This is seen in tall grassland
areas in Kwazulu-Natal that are normally dominated by thatch grass. Where
46
overgrazing has occurred, the less palatable, Catstail dropseed has become
the dominant grass.
3. Draining of wetlands
The drainage of wetlands for building or crop planting permanently alters the
environment. This results in the disappearance of wetland climax species, e.g. frogs,
reeds, etc.
4. Climate change
Climate change will definitely affect successional endpoints, e.g. some grassland
parts of the Congo will get wetter and change into forest communities.
Countries in east Africa, e.g. Kenya, may get drier, which will change their climax
communities.
5. Invasion by aliens
Invasive species are replacing the once dominant species in climax communities.
For example:
 the triffid weed, a category 1 invasive plant, has invaded the grassland,
savannah and forest biomes. This can be seen in parts of the Hluhluwe Game
Reserve.
Triffid weed
 orange lantana, a very vigorous, invasive weed species, is taking over some
grassland areas. This is very noticeable in parts of the Eastern Cape.
orange lantana
Learning activity 12 Succession

1.Two successions, primary and secondary are shown in the following two diagrams,
A and B. After carefully reading the preceding few pages, complete the missing
headings, A and B, and information, 1 to 5 on each drawing. (12+20)
47
Diagram A
Diagram B
1.Mention two features of early successional plants that enable them to easily invade
an open area. [2]
2.The first stage of primary succession is different from that of secondary

succession. Decide which of the following (1 to 8) describes the situation in a
2.1primary succession __________________
2.2.secondary succession _________________.
Write the numbers above for each type of succession.
48
1. no soil in the beginning
2. first colonisers, grasses and annuals
3. usually more rapid
4. initial pioneer species, lichen and moss
5. slower process
6. always begins on a barren surface
7. colonising area already has soil with nutrients
8. organic matter and seeds in area
[8]
3.The following sketch represents how primary succession in a pond could occur.
3.1Study both the diagram and the selection (A to F) of organisms/phases and write
the correct letter next to the relevant number. (6)
AHygrophilous grasses
BRooted in water, having aerial parts, e.g. reeds, sedges, bulrushes
CStable-state in transition to an alternative climax community
DSubmerged plants
EGrasses and shrubs
FFloating plants, e.g. water lilies
3.2Underline the correct alternative from between the brackets. Slowly over time the
pond will fill up through (a) (evaporation/siltation) and dry unless there is some
mechanism to maintain water (b) (depth/purity), e.g. (c) (crocodile / hippo) paths
which keep channels open. (3)
[9]
4.The following sketch represents how primary succession on a beach could occur.
4.1Study the diagram and write down the stages of succession from 1 to 3. (3)
4.2At the different periods of the three stages various plant types occur. Next to the
three stages of succession, write down the letters, A to F of the plant types that will
occur in each of these periods. (6)
AHardy shrubs close over pioneers, which disappear
BSemi-stable state (climax) to an alternative endpoint
CPioneers being invaded by hardy shrubs

49
DPioneers help accumulate sand; build and stabilise dunes
EHardy shrubs colonised by early succession forest trees
FForest closes over shrubs, which disappear
[9]
Total [60]
Learning activity 13 Investigation
Aim
Take note of the succession of primary plants and animals in a disturbed area.
Procedure
Identify an area in or near your school grounds where succession is or has taken
place, e.g. a roadside that has been scraped or the goal area on the sports field at
the end of a season.
Write down the date and then make a list of any primary succession plants such as
lichens as well as any faunal pioneers that are there.
Continue to check on the area every two weeks, listing the date and any new
species. Are there secondary succession species?
Compare your list with those of other learners.
1 2 3 4 5 6 7 8 9 10
1. Multiple choice
alternative and write it below the relevant number in the table above.
Base your answers to questions 1 to 4 on the following table and your knowledge of
succession.
Stage Dominant flora
1 none (freshly ploughed land)
2 mixed grasses
50
3 thorny shrubs
4 Acacia and Shepherds’ trees
5 Yellowwood – Cape Chestnut forest
1. Which stage represents a pioneer community? (a) 1; (b) 2; (c) 3; (d) 3.

2. Stages 1 to 5 are part of: (a) primary succession; (b) cover cropping; (c)
secondary succession; (d) natural selection.
3. In the Eastern Cape which fauna would most likely be associated with stage
5? (a) eland; (b) African Wild dogs; (c) bush pig;(d) blue crane?
4. Which stage best represents a highveld climax community? (a) 2; (b) 3; (c) 4;
(d) 5.
Use the diagram below and your knowledge of the living environment to
answer questions 5 to 7.
Four stages of a Biological Process
5. What would be the main life-form most likely to be found in stage 1? (a) ferns;
(b) pioneer species; (c) trees; (d) mushrooms.
6. Stage 4 will continue until it is altered by: (a) a major change in an abiotic
factor. (b) seasonal dieback of vegetation. (c) the reappearance of lichens.
(d) a growth in width of the trees.
7. What is a major limiting biotic factor for animal succession in each stage? (a)
plant species; (b) sunlight; (c) mineral salts; (d) moisture.
8. In a pool, which one of the following changes would most likely lead to
terrestrial succession? (a) a decrease in the number of suspended particles in
the pond water. (b) an increase in current flow of the pond water. (c) an
increase in sediment, fallen leaves and branches accumulating on the bottom
51
of the pond. (d) a decrease in the number of diverse organisms in the shallow
water of the pond.
9. Which statement concerning the climax stage of an ecological succession is
correct? (a) It is the first community to inhabit an area. (b) It consists entirely
of plants. (c) It persists until the environment changes. (d) It changes rapidly.
10. Starting on exposed rock, what is the usual ecological succession of
organisms?
(a) shrubs --> grasses --> lichens --> trees
(b) lichens --> shrubs --> grasses --> trees
(c) grasses --> shrubs --> lichens --> trees
(d) lichens --> grasses --> shrubs --> trees
[10]
2. Terms
Give the correct term for each of the following:
1.Any change in plant communities over time
2.A common pioneer organism in a primary succession
3.The community that is the final semi-stable state of a succession
4.The first organism in a succession
5.Succession where there have been no plants.
[5]
3. True and false

Write down if the following statements are true or false. If false, write down the
incorrect word/term followed by the correct word/term.
1.The mix of species changes continually during and secondary

succession.
2.When succession starts from a bare habitat, e.g. bare rock, it is

called a secondary succession.
3.The semi-stable stage that is established in an area as a result of

ecological succession is known as the pioneer stage.
4.Palm trees are the most likely pioneer organisms on a newly formed
volcanic island.
5.Community structure is not static, itis determined over time by

succession, which takes place because of disturbances or competitive
interactions.
52
[5]
Total [20]
5. Social organisation
Very few animals live in a completely solitary way. Many live in groups or colonies
that show social organisation for all or parts of their lives.
social organisation = structure of relationships within a group
To be socially organised certain features must be divided among the group. These
include:
 resources, e.g. food, territories and nest sites

 activities, e.g. protection and other skills.
What is the value of social organisation?

The two groups that have developed social organisation to a particularly high degree
are insects, e.g. termites and bees and mammals, e.g. wild dogs and naked mole
rats.
Social organisation is very valuable as it improves the survival and reproductive

success of an individual. Social organisation makes it easier to:
 avoid being attacked by predators

 find food by hunting collectively
 divide labour among individuals
 find mates
 protect resources
 regulate population size
Learning Activity 15 Social organisation
Devise a learning diagram to show the value of social organisation.
1. Herds or flocks as a predator avoidance strategy

The biggest advantage of forming a large group (flocking) is that the safety of the
group is increased by avoiding and defending against predators. Although a
predator can see a large group more easily, less prey are probably captured
because of the following:
53
 With many eyes and ears, the group as a whole is more watchful, particularly
the individuals on the edge of the group.
 A large herd or flock can mob a predator.
mob = to surround and overpower
 The greater the number of individuals in a group, the greater the survival
chances are of the individual. This is known as the dilution effect.
 As a predator tries to single out its prey, the herd scatters in all directions,
confusing the predator. This is known as the confusion and distraction
effect.
 The members of a flock protect those who are moulting and vulnerable
against predators, e.g. penguins.
 During migration, the inexperienced are given guidance and protection by the
herd or flock against predation.
Zebras exhibit many of the above strategies to ensure their survival but in addition,
the vertical stripes of a zebra cause individual zebras in a herd to blend together
when viewed from a distance. To a predator, the huge shape is not recognized as a
potential source of food.
A herd of zebra
Learning Activity 16
Herds or flocks as a predator avoidance strategy
Devise a simple learning diagram in the space on the next page to show how a flock
or herd can offer protection against an attack by a predator.
54
2. Packs as a successful hunting strategy
The African Wild dogs are highly social animals with complex methods of
communication that keep the group functioning together, especially when hunting.
They are slim, long-legged animals about the size of an Alsatian dog. Their coats are
a mottled combination of tan, black and white with each individual having its own
unique pattern. The African Wild dog differs from true dogs and wolves in that it has
only four, not five toes on each foot. Its large rounded ears are characteristic and
result in it having very sharp sense of hearing. Why?
In South Africa wild dogs are confined to game reserves, such as the Kruger,
Hluhluwe-Umfolozi Park and Shamwari. In the Bushmanland region of Namibia there
are still some free-roaming packs.
How do they catch their prey?

The African wild dogs have one of the highest success rates of any predator species
in Africa, catching their prey in eight out of ten attempts. They hunt in very closely-
knit packs of up to fifteen adults. Their prey includes antelope, zebra and warthog.
 After detecting their prey, by sight or sound, they chase it at a fast run, about
45 km/h. As they are tireless runners, they can chase their prey for an hour or
more, often covering many kilometers.
 When the prey tires they immobilise it; one dog grabs its tail and the other its
upper lip. The rest of the pack then kills the prey quickly and efficiently.
 The whole pack shares in the kill with the young feeding first, which is
unusual. Wild dogs are the only carnivorous species in which this happens.
 Wild dogs left behind in the den – the dominant female and the pups, or those
unable to hunt – the sick, injured and very old, are fed on regurgitated meat
(partially digested meat brought up from the stomach to the mouth).
In this most efficient system of hunting and feeding, the needs of the whole pack are
satisfied and the survival of the species is ensured.
Animals with a dominant breeding pair
55
There are many species of animals that have a social grouping in which there are
dominant male and female breeding pairs, e.g. wild dogs.
There is a strict ranking system within the pack of African wild dogs, led by
the dominant alpha male and female who stay mates for life and prevent other
females from breeding. They, therefore, are the only members of the pack that
breed.
What happens to the offspring?
 The females reach sexual maturity at eighteen months to two years, at which
point they leave to join a new pack.
 The males remain with their pack for the rest of their lives, which last, on
average, eleven years.
What are the benefits of this type of social organization?
 The dominant pair keeps the pack under control which operates as a highly
successful unit to ensure the survival of the species.
 Raising the pups of the dominant breeding pair and caring for old or sick
individuals is a group task.
 Subordinate members of the group benefit too in that they have access to
mates and other resources shared by the group. At a later stage in their lives,
these members may become dominant as well.
Note:
Wild dogs are the second most endangered carnivore (after the Ethiopian wolf) in
Africa. Hunting, habitat loss and the fact that they are particularly vulnerable to the
spread of disease by domestic dogs are the main causes for the continent’s African
Wild Dog loss.
4. Division of tasks among castes

Most animals that live in social groups (e.g. termites, bees, wasps and naked mole
rats) have division of tasks or labour within the group. Each individual in the group
has a role to play that is important for the success of the group as a whole.
56
Eusocial animals are the most advanced form of social organisation. These
animalslive in colonies in which:
 there is a dominant breeding pair or a single female (queen).

 the non-breeding animals have different tasks to perform, i.e. there is a
strict caste system. Tasks include collecting food, caring for the young and
building, maintaining and protecting the nest.
Because of environmental pressures such as shortage of resources, individuals of

such colonies could not survive on their own. Eusociality is a major evolutionary
innovationwhich has involved changes in life history, structure and behaviour.
Termites and ants are all eusocial, as are some species of bee and wasp and a few
very unusual mammals such as the naked mole-rat.
eusocial = species that exhibit the highest level of social organisation
Termites – eusocial insects

Termites are a group of cellulose-eating insects, living in a colony which is a highly
organised, integrated unit. The African and Australian termites create large mounds
of soil which are cemented with faeces and saliva called termetaria.
A termite mound
Their caste system includes:
Reproductives: this group is made up of;
 Alates: Each termite colony is founded by two winged termites called alates.
These winged termites appear in the rainy season and mate. Each pair can
found a new colony.
 Queen and King: After losing their wings, the pair burrow underground. The
female becomes the queen and the male the king of the new colony. The
eggs that the queen continuously lays, hatch into nymphs and these young
termites will grow into other castes that have different roles in the colony. The
queen lays thousands of eggs each week and her egg-filled abdomen can
extend up to 10 cm in some species. Unlike bees, wasps and ants, the king
plays a continuous part, mating with the queen at regular intervals.
 Young reproductives: These are the young termites that will either become
the new alates (and therefore new queens and kings) or supplementary
reproductives that can replace the queen and king if they should die.
Workers: Most of the termites in a colony are workers. Unlike ants, bees and wasps,
termite workers may be male or female. They make tunnels, build the termite mound,
forage for food, look after the eggs and nymphs and feed all the other members of
the colony.
They can digest the cellulose in leaves and wood by using bacteria and protozoa in
their stomachs and then pass this partially digested food to the king and queen, the
nymphs and the soldiers – either regurgitated or as faecal pellets.
57
Soldiers: These termites make up around 5% of the colony and develop huge biting
or squirting mouthparts (depending on the species) that help with the defense of the
colony, especially from ants.
How is the ratio of castes regulated?

Normally there is a king and queen and a set ratio of soldiers to workers and
nymphs. It is known that all nymphs are genetically identical at hatching and that all
could develop into any of the three major castes.
 If individuals of any caste are lost, additional members of that caste develop
from nymphs to restore the balance.
 If there is overproduction of a caste, selective cannibalism restores the
balance.
Both reproductives and soldier castes secrete a pheromone (chemical message) that
is transmitted through food sharing and grooming to other members of the colony
which inhibits development of reproductives or soldiers. If the caste balance of the
colony is upset, some undifferentiated nymphs do not receive the ‘pheromone
message’ and develop into reproductives or soldiers, thereby restoring the balance.
Division of labour
Question 1
Name:
1.the most advanced form of social organisation
2.winged reproductive
3.immature termites
4.the carbohydrate in plants which termites are able to digest
5.the micro-organisms that aid this digestion
6.chemical messages that prevent the development of reproductives or soldiers
7.a process that might help to reduce the numbers in a caste if overpopulation
occurs.
[7]
Question 2
The termite colony is very successful because work is divided among specialists with
each type of individual performing a specific job. Complete the following table.
58
Caste Function
1.
2.
3.
[9]
Total [16]
Short questions
1. Multiple choice
alternative and write it below the relevant number in the table.
1 2 3 4 5
1. Social organisation leads to an increase in the population size and in chances

of survival. Which of the following best describes the phenomenon of social
organisation? (a) A beehive made up of worker bees, a queen and drones; (b)
Elephants looking after their babies; (c) An injured impala trying to keep pace
with the rest of the herd; (d) A hyena hunting for its prey.
2. Which is not true of the value of social organisation? It is easier to: (a) find
mates; (b) protect against physical harm and predators; (c) produce a large
population; (d) find food.
3. Which is not true of termites? (a) The king remains with the queen in the nest.
(b) All the workers are males. (c) Both reproductives and soldiers secrete
pheromones. (d) Ants are the main enemy.
4. Wild dogs are the only carnivorous species to: (a) hunt at night; (b) after a kill
feed their young first; (c) to catch their prey six out of ten times; (d) chase their
prey for a long time.
5. Dilution effect is caused by: (a) the scattering of the herd in all directions; (b)
more females joining a pack; (c) adult males leaving the pack; (d) increased
number of individuals ensuring the best chance of survival of a group.
[5]
59
2. True and False
Write down if the following statements are true or false. If the statement is false, fill in
the incorrect and correct words alongside your answer.
1.Pheromones secreted by the workers, stimulate the development of

reproductives and soldiers.
2.The African wild dogs are the most efficient prey species on the
African continent as they catch 80% of the animals they chase.
3.The non-breeding animals in colonies carry out different functions.
4.The scattering of the herd when a predator singles out its prey is
called the dilution effect.
5.Eusociality is the most advanced form of social organisation shown by

mammals.
[8]
Total [13]
6. Human population dynamics

It is estimated that 10 000 years ago there were no more than 10 million people on
earth. This population remained fairly constant as death rates were high because:
 people died from starvation and disease

 infant mortality rates were very high.
But in the last 1 000 years, the population growth has increased exponentially.
exponentially = increasing more and more rapidly
The graph below shows how the size of the population has grown.
What is the current human population?
In recent years, the human population:
 is estimated to be just over 7.3 billion people (July 2015)

 is increased by approximately 216 000 people each day, i.e. an annual
increase of 83 million people. Virtually all the growth is in developing
countries, with growth of the youth population occurring in the poorest of
these countries.
Note:
China has the largest population of any country (1.40 billion people = 20% of the
world’s population)
60
India has the second largest population (1.28 billion people = 17% of the world’s
population).
What has caused this exponential growth?
The recent alarming population growth is mainly due to the fact that humans have:
 reduced environmental resistance and

 increased the carrying capacity of the world’s food-producing regions.
This has been done in two ways:
1.Food production has increased substantially. This is due to:
 more land being cultivated

 improved methods of food production such as using artificial fertilizers to
increase the yield of monoculture crops.
2.Methods of treating diseases have improved greatly. This has allowed more
people to stay alive to reproduce.
Do countries of the world differ?
The countries of the world can be divided into two broad groups:
1.More developed countries (MDCs) that have a:
 slow population growth, i.e. 0.1% per year

 high standard of living, e.g. North America, Europe, Japan and Australia.
2.Less developed countries (LDCs) that have a:
 rapid population growth, i.e. 1.6% per year

 lower standard of living, e.g. Latin America, Africa and Asia.
What about the future?
 It is thought that, for the next 150 years, human population growth will be less
exponential with a more logistic type of growth form
 Industrialised countries (MDCs) have already shifted to a stable population as
population growth has begun to decline. This is because birth rates have
fallen due to late marriages, birth control and sexual abstinence, e.g. Japan,
Germany and Britain.
 The populations of LDCs will continue to grow as improved medical
treatments have enabled more women in their reproductive years to live
longer and therefore produce more babies.
What is the ecological footprint of MDCs and LDCs?

Human population growth is placing extreme pressure on the earth’s resources and
the environment.
 Even though LDCs have higher growth rates and larger populations, the
environmental pressures are primarily due to the MDCs.
61
 The MDCs are responsible for more total pollution and more total
consumption than LDCs.
 The MDCs account for 22% of the world’s population, yet they produce 90%
of the hazardous waste and use more resources.
Makes you think, doesn’t it?
Human population
Question 1
The table below gives the approximate world human population at various times
since 1640.
Year AC Approximate world population (millions)
1640 500
1840 1000
1900 1500
1920 1750
1950 2500
1960 3000
1980 4000
2000 6500
2020 ?
62
1.Plot the data on the graph grid below, putting ‘Year AD’ on the horizontal axis
beginning at 1640 and ‘Number of people’ on the vertical axis. Include the year 2020
on your time scale. (4)
2.According to your graph what is the predicted world human population in the year
AD 2020? (1)
3.How many years did it take the population to increase from:
3.1.1 000 million to 2 000 million? _______
3.2.2 000 million to 3 000 million? _______
3.3.3 000 million to 4 000 million? _____ (3)
4.Make a list of three factors that normally stop animal populations from growing
indefinitely. (3)
5.For each of these factors, suggest why it has failed to control the human
population. (3 x 2 = 6)
6.Which two parameters could reduce the world’s population growth? (2)
7.Which do you think would be the more desirable way of limiting population growth?
(1)
8.Suggest ways of achieving this. (2)
Total [22]
What is a population pyramid?

A population pyramid, also called an age-sex pyramid, is a bar graph that shows the
composition, by age and sex, of a nation's population at the time of a census. It is a
convenient way to show, in visual form, how a national population is made up.
A population contains three major age/sex groups:
 pre-reproductive
 reproductive
 post-reproductive.
The age structure of a population is determined by what proportion of the population

falls into each of these age groups.
age structure = the relative numbers of individuals of each age in a population
How is a population graph constructed?

The graph typically consists of two back-to-back bar graphs, with the population
numbers plotted on the horizontal axis and age on the vertical axis.
63
 The top of the pyramid shows the older population; the bottom of the pyramid
shows the younger population.
 The number of males is shown on the left and the number of females on the
right in five-year age groups. This may be shown as a percentage of males
and females in each age group or in actual numbers. There tend to be more
females than males in the older age groups.
As you read about the structure of a pyramid, take note of the diagram below.
What do the different pyramid shapes depict?

The shapes of population pyramids show three types of population growth. See the
next column.
1. Rapidly growing population
High birth rate; rapid fall in each upward age group due to high death rates, short life
expectancy as found in LDCs, e.g. Africa, Asia and South America.
2. Stable population
64
Declining birth rate; low death rate; more people living to old age as found in MCDs
e.g. Canada, Australia.
3. Declining population
Low birth rate, low death rate; higher dependency ratio; longer life expectancy as
found in affluent countries, e.g. Sweden, Norway.
Note:
If the pre-reproductive age group is the largest, the population will increase; if it is the
smallest, the population will decrease.
65
In general, a population with more old, non-productive individuals will grow more
slowly than a population with a larger percentage of young individuals of
reproductive age.
What is the purpose of population graphs?

A great deal of information about a population can be read from population graphs,
e.g. they can:
 provide a quick way to assess how rapidly or slowly a nation’s population is

growing.
 show if a country is more developed or less developed.
 show how many people of each age range live in a country.
 show the history of a nation’s growth.
 be useful in determining the number of economic dependents being
supported, i.e. those under 15 years of age and over 65. Ideally the economy
should be planned so that the working population supports these dependents.
Note:
 0 – 15 year olds represent children who form an economically dependent

group
 15 – 65 year olds represent the productive, working group that forms the
labour force of a country
 65+ represent senior citizens who are also dependent on the country’s work
force.
What factors can cause the make-up of a population to change?

The most dramatic changes in the make-up of a population may be due to:
 HIV/AIDS causing the deaths of many sexually active young men and women
particularly in developing countries.
 high proportions of young immigrants being rapidly absorbed, or losses due
to emigration of able-bodied young adults.
 losses due to able bodied men fighting wars.
 reduced birthrates during times of economic crisis.
South Africa’s population growth

For 2014, Statistics South Africa (Stats SA) estimates the mid-year population as 54
million. In 1960 it was 17.4 million, i.e. an increase of over 190% during the last 54
years.
What a frightening increase!
Despite this increase, the rate of population increase is dropping as seen in the
figures below:
1993: 2.4%
1996: 1.9%
2004: 1%
66
2009: 0.28%
This is mainly due to HIV/AIDS deaths.
Note:
The estimated overall HIV prevalence rate is approximately 10,2% of the total South
African population. The total number of people living with HIV is estimated at
approximately 5,51 million in 2014. For adults aged 15–49 years, an estimated
16,8% of the population is HIV positive.
What about the future?

Will the population profile change? Will the population continue to grow? To find out
the answers to these and many other questions, study the population pyramids
below.
South African population pyramids

Study the following population pyramids indicating the age and sex distribution in
South Africa from 1990 to a projected distribution in 2050 and answer the questions
that follow.
67
The human population has exploded
1.Describe the type of population growth form that occurred in 1990. (4)
2.Which age group had or is projected to have the greatest proportion of people in:
1990: ______, 2010:______, 2050:_____? (3)
3.In 2050 will there be more people in your age group or in the age group below
yours? (2)
4.By studying these pyramids, complete the table below and then calculate how
many less babies are predicted to be born in South Africa in 2050 compared with the
numbers predicted to be born in 2010.
68
Predicted number of babies born in millions
Year Female babies Male babies Total babies
2010 1.6 3.30
2050 0.95 0.99
5.There should therefore be approximately __________ less babies born in 2050

than in 2010. (3)
6.Can the predicted graph for 2050 be described as a stable population growth
form? Explain your answer. (4)
7.Describe in your own words the changes that have taken place and are predicted
to take place in the South African population from 1990 to 2050. Explain why you
think these changes will occur. (8)
Total [24]
Will the environment survive the human explosion?

In Grade 11 you learnt that an ecological footprint is a measure of human demand
on the earth’s ecosystems. It represents the amount of biologically productive land
and sea area necessary to supply the resources a human population consumes, and
to assimilate the waste generated.
In other words, the footprint accounts for all demands on the biosphere, including:
 carbon emissions from fossil fuel

 demand on food sources,
 the quantity of living resources required to make the goods we consume
 the amount of land we take out of production when we pave it over to build
cities and roads.
At present, the total world ecological footprint is 2.7 global hectares per person. As
the world-average biocapacity is 2.1 global hectares per person, there is
an ecological deficit of 0.6 global hectares per person. This will change from
year to year.
biocapacity = the amount of productive land and water available to produce the
resources we use and to absorb the waste we produce
Note:
 A country with an ecological deficit is called ecological debtor country.

 If a country does not have an ecological deficit, it is called an ecological
creditor country.
69
What can be learnt from ecological footprints?
Ecological footprinting is now widely used around the globe as an indicator of
environmental sustainability and has shown that:
 Many MCD countries are running ecological deficits, with footprints larger than
their biological capacity. This deficit is compensated for by using resources
from other countries.
 MCDs have the largest ecological footprints. The economy of countries such
as the United States requires far more land, energy and water and produces
much more waste than LDCs, even though the latter have most of the world’s
population.
 LCD countries may use very little of the world’s resources but their urban
population is increasing rapidly as is their standard of living, so they are
consuming more and more resources.
 If ecological footprints continue to increase, the natural resources needed to
maintain human life will be greatly reduced and, unless we try and solve this
problem, our planet earth will be permanently damaged.
Note:
85% of the world population is living in a country that is running on a biocapacity
deficit.
What is your ecological footprint?

One method of calculating your ecological footprint is using the Ecological Footprint
Calculator, hosted by Earth Day Network. Go to www.earthday.org and click on Your
Ecological Footprint.
Country Ecological footprint per person in hectares
US of America 9.57
France 5.74
United Kingdom 5.3
Israel 4.8
South Africa 2.7
Argentina 2.5
70
Ethiopia 1.4
India 0.9
Zambia 0.8
Afghanistan 0.5
Ecological footprints of various countries
Ecological footprint
1.List three activities that you do in everyday life that increases your ecological
footprint. (3)
2.List three activities you could do in everyday life to help minimise your footprint. (3)
3.What are some of the factors that may contribute to people living in Europe having
a larger ecological footprint than people living in a developing country such as
Ethiopia? (4)
4.How many Ethiopians would use the same amount of resources as one average
American? (2) Use the table above and show your calculations. (2)
Total [14]
Human need for land versus conservation
South Africa, like other countries, is dependent on the diversity and richness of its
natural resources to sustain its population and to contribute to its economic growth.
But, as the human population increases and expectations of living standards rise,
these natural resources are put under pressure as more and more natural habitats
are converted to agriculture, forestry, mining activities and human settlements.
 Towns and cities generate and accumulate wealth and are centres of
education, economic opportunity, employment and culture, but they take over
areas of productive agricultural land and use large quantities of water, energy,
foodstuffs and raw materials and generate enormous quantities of waste and
pollution.
 Agriculture, forestry and mining are also important for national growth and
development, but they alter the natural environment and cause tremendous
environmental degradation.
Rapid population growth can result in the exploitation of natural resources.

Developing countries are often faced with the dilemma of ‘food now versus natural
resources later’.
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In all forms of land use, therefore, a compromise has to be reached between
economic development and environmental degradation.
Conservation of land and marine environments

It is therefore important to conserve as much of the remaining natural environment.
South Africa set itself the target of increasing land under formal conservation from
5.4% in 1994 to 8% in 2010, and its marine protected areas from 11% to 20%.
conservation = protecting something and keeping it in a healthy state
For example:
 The original Kalahari Gemsbok National Park joined up with the bordering
Gemsbok National Park in Botswana in 1998 to form the Kgalagadi
Transfrontier Park– one of the largest conservation areas in the world.
 The Addo National Elephant Park has recently been expanded to form a
mega-park, the Greater Addo Elephant National Park.
This is probably the only park in the world where the ‘Big 7’ can be found in
their natural habitat – elephant, rhinoceros, lion, buffalo, leopard, whale and
the great white shark.
Whose responsibility is it?

Under schedule four of the constitution, provinces and the national
government share environmental responsibilities and are committed to the basic
principles of sustainable development.
sustainable development = the development that meets the needs of the present
while not compromising the needs of future generations
Currently, however, this is not happening. For many reasons, development planning
does not pay sufficient attention to environmental issues. In 2005, environmental
management inspectors (EMI) the Green Scorpions were formed to enforce
environmental laws.
Contentious issues or areas of conflict facing environmentalists are:
 The use of traditional land for conservation or game reserves.

 Tensions caused by hunting and/or poaching in proclaimed nature or game
reserves.
 Harvesting of plants and animals for traditional medicines.
 Implementation of ecotourism as a sustainable way of using a conservation
area for leisure and at the same time producing economic benefits for the
local people who are living in that conservation area.
Class discussion
Have a class discussion as to how the environment and our natural resources may
be preserved for future generations in the face of increased industrialisation.
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Short questions
1. True and False

Write down if the following statements are true or false. If false write the wrong word
followed by the correct word.
T/F Correct
word
1.A declining population is typified by having a low birth rate and

a low death rate.
2.15 to 35 year olds represent the labour force of a country.
3.LDCs have a high population growth and high living standards.
4.MDCs have populations with a large work force and a small

number of senior citizens.
5.Improved health care and large-scale food production have

enabled the global human population to increase exponentially.
6.Towns and cities generate and accumulate wealth, consuming

little of the natural resources.
7.The world’s ecological deficit is 1.6 global hectares per person.

[12]
2. Terms
1.The type of population increase that occurs more and more rapidly
2.Protecting something and keeping it in a healthy state
3.The amount of productive land and water available to produce the resources
we use
4.The development that meets the needs of the present while not compromising
the needs of future generations
[4]
3. Items and statements

Write down your choice in the appropriate space by using the following codes:
Aif only item 1 relates to the statement
73
Bif only item 2 relates to the statement
Cif both items 1 and 2 relate to the statement
Dif neither item 1 or 2 relate to the statement
Statements Answers Items
a population with a large number of

1. 1.more developed country senior citizens
2.less developed – country
2. 1.improved health care human population explosion
2.large-scale food production

3. 1.national growth and agriculture, forestry and mining
development
2.environmental degradation
4. 1.2.7 global hectares per world’s biocapacity
person
2.0.6 global hectares per

person
[4]
Human endocrine system
The nervous and endocrine systems enable animals to response to external

changes and to control conditions inside their bodies.
Chemical co-ordination
Chemical co-ordination may be described as a slow, prolonged process of
communicating information throughout the body by way of chemicals
called hormones. A variety of hormones are secreted by special glands or tissue
called endocrine glands. The endocrine system works with the nervous system.
What is a hormone?
A hormone is an organic chemical substance, usually a protein but sometimes a
steroid, secreted by an endocrine gland and carried in the blood stream to its target
organ/s where it regulates metabolic reactions. Hormones do not last long in the
body as they are broken down by enzymes.
What is a target organ?

Although hormones are carried in the blood throughout the body, they only affect
certain cells. The specific cells that respond to a given hormone have receptor sites
74
for that hormone. These cells are known as target tissue or target organs. They can
be a single gland or organ or scattered throughout the body.
What is an endocrine gland?

An endocrine gland is a vascular, ductless gland that secretes hormones which are
carried in the bloodstream to their target organs.
vascular = richly supplied with blood vessels
How do exo– and endocrine glands differ?
 The secretions of an exocrine gland are carried in ducts to where they are
needed, e.g. salivary glands, liver, pancreas.
 Endocrine glands do not have ducts and their secretions are carried in
the bloodstream to their target organs.
Endocrine glands in the body
There are many endocrine glands in the body.
Diagram to show the position of some of the endocrine glands
75
76
1. Hypothalamus
The hypothalamus is part of the brain, situated above the pituitary gland. It secretes,
amongst others, the hormone ADH (anti-diuretic hormone).
What is the role of ADH?

Osmoreceptors in the blood vessels of hypothalamus detect an increase in the
osmolarity (low water levels) of the blood. The hypothalamus responds and releases
ADH.
ADH helps to conserve water if the body is dehydrated. It does this by causing
more water to be reabsorbed back into the blood from the collecting ducts of the
kidney, so less water is lost in urine.
2. Pituitary gland
This gland acts as the chemical co-ordinator of most of the other endocrine glands
and is therefore often called the ‘master gland’. It is attached to the hypothalamus
at the base of the brain by a short stalk.
In some text books the pituitary is called the hypophysis.
Position of pituitary
What hormones are secreted by the pituitary?

The pituitary gland secretes many hormones. The following is a brief summary of
some of these hormones and their functions.
1. Thyroid stimulating hormone (TSH), which stimulates the thyroid gland to

secrete its hormone, thyroxin.
2. Follicle stimulating hormone (FSH)
o In females FSH stimulates oogenesis in the ovary, i.e. the formation of
eggs (ova).
o In males FSH stimulates spermatogenesis in the testis, i.e. sperm
formation.
3. Luteinising hormone (LH), which stimulates ovulation (release of an egg)
from the ovary and the formation of the corpus luteum.
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4. Prolactin, which stimulates the production of milk in the female mammary
glands after the birth of the baby. This will continue for as long as the baby
suckles. Prolactin is also responsible for much of the maternal instinct.
5. Adrenocorticotropic hormone (ACTH), which stimulates the adrenal cortex
to secrete the hormones, cortisone and aldosterone.
6. Interstitial cell stimulating hormone (ICSH), which stimulates the testis to
secrete testosterone.
7. Growth hormone (GH) or STH (somatotrophic hormone), which promotes
skeletal and muscular growth. It does this by stimulating the synthesis of
proteins.
What growth disorders can occur?

Too much or too little growth hormone causes growth disorders.
hypersecretion = over secretion of a hormone
hyposecretion = under secretion of a hormone
It is easy to confuse ‘hypo-’ and ‘hyper-’ – be careful!
In prepubertal (before growth stops) children:
 hypersecretion of growth hormone results in overdevelopment of the skeleton

(tall stature). This condition is known as gigantism. This is usually caused by a
tumour in the pituitary gland and is extremely rare.
 hyposecretion of growth hormone results in underdevelopment of the skeleton

(short stature). This is known as pituitary dwarfism and has some of the
following features.
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–Although height is reduced (they can be as short as 91–122 cm) the body
proportions are normal.
–They are not mentally retarded but are often sexually immature.
They can be treated by injections of synthetic growth hormone (STH)

produced by genetically engineered bacteria.
Pituitary dwarfs
Did you know?

There are two kinds of dwarfs.
 pituitary dwarf or midget (see above).

 a defective gene causes the other type. Such a person looks malformed with
very short arms and legs but a normal sized torso and head.
In adults, over-secretion of GH leads to a condition called acromegaly, a condition

where the bones of the face, hands and feet are enlarged. The thickening of soft
tissues leads to enlarged features and an enlarged tongue.
79
To show the enlargement of the face, skull and hands in patients with
acromegaly
Learning activity 1
Hypothalamus and pituitary hormones

Complete the following table.
Hormone Target organ(s) Function
STH 1. Promotes bone and muscle growth
2. 3. Stimulates the secretion of thyroxin
4. Nephrons of the kidneys 5.
LH 6. 7.
8. 9. Stimulates spermatogenesis
10 11 Stimulates oogenesis
12 Mammary glands 13
Total [13]
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3. Thyroid gland
The two lobes of the butterfly-shaped gland are found on either side of the trachea
just below the larynx (voice box) in the front of the neck.
Position of thyroid gland
What hormone does the thyroid secrete?

The most important hormone secreted by the thyroid is thyroxin.
81
Note:
 Iodine is an essential element needed for the production of thyroxin. Iodine is

found in sea food, sea salt or iodised salt.
 A goitre may develop if levels of iodine are low.
What are the functions of thyroxin?

Thyroxin has many effects, three of which are mentioned below.
1. It increases the basal metabolic rate (and therefore production of body

heat) in all body cells. It does this by controlling the rate of cellular respiration.
basal metabolic rate = amount of energy the body needs to keep functioning
while at rest
2. It promotes the normal functioning of the heart.
3. It promotes the normal functioning of the nervous system by increasing
nervous activity and sharpening alertness and reflexes.
What disorders can occur?

Hypothyroidism, i.e. producing too little thyroxin, causes a low metabolic rate.
 In adults hypothyroidism results in myxoedema, a condition of mental and

physical sluggishness, with low blood pressure, a slow heart and respiratory
rate and also a low body temperature.
 In children hypothyroidism results in cretinism, a condition in which a child
does not grow physically, has immature sexual development and is mentally
retarded.
A cretin
Hypothyroidism can be treated with iodine supplements or synthetic iodine.

However, once developmental and mental abnormalities have occurred in a child,
they cannot be reversed.
Hyperthyroidism, i.e. producing too much thyroxin, causes a high metabolic rate.
 The body temperature is high and sweating increases.

 The heart and respiratory rate and blood pressure increases.
 There are muscular tremors and nervousness.
 Sufferers often have a swollen thyroid gland, known as an exophthalmic
goitre.
A goitre
Keeping thyroxin in the blood constant

This is done by a control mechanism known as negative feedback. To bring this
about the thyroid and pituitary glands interact as follows:
82
 The pituitary detects a decreased level of thyroxin in the blood, so it secretes
more TSH.
 The TSH stimulates the thyroid to secrete more thyroxin, returning its level to
normal.
 The higher level of thyroxin inhibits further secretion of TSH from the pituitary.
Negative feedback mechanism controlling thyroxin production
The negative feedback mechanism will therefore ensure that the level of thyroxin in
the blood is kept at the correct level (set point) at all times.
Learning activity 2
Thyroid gland and its functioning
Study the diagram below and answer the questions that follow.
1.What structures do numbers 1 and 3 represent? (2)
1.______________________________
3.______________________________
2.What hormone does number 2 represent? (1)
83
3.Name three target organs (numbers 4, 5 and 6) of thyroxin. Mention, in each case,
the effect the hormone will have. (3 x 2 = 6)
4.Negative feedback (number 7) plays a role in controlling the amount of thyroxin

released into the blood. Explain what happens if thyroxin level in blood becomes too
high. (3)
Total [12]
Did you enjoy this type of exercise in which you find most of the answers from a
diagram?
Homeostasis is a state of balance
Homeostasis and negative feedback control

Tissue fluid and blood are extracellular fluids and together form the internal
environment of the body.
tissue fluid = fluid that surrounds all body cells
The external environment is the surroundings where the organism lives.
For cells to function properly the optimal levels of many factors in the internal
environment must remain constant, e.g. concentration of water, electrolytes, carbon
dioxide, oxygen, glucose and other solutes as well as temperature and pH.
The process of maintaining the internal environment in a constant optimal state,

despite constant changes in the external environment, is called homeostasis.
homeostasis = staying the same
How is homeostasis maintained?

To be able to keep this ‘steady state’ it is important to detect any change from the set
point or norm and then to be able to correct this change or deviation...
Thus, homeostasis is the ability of an individual to return a particular factor to the set
point or norm.
How is this brought about?
84
The major mechanism that enables an organism to correct any change from the set
point and so maintain homeostasis is negative feedback.
Negative feedback is a control mechanism whereby a change from the set point of
any factor is corrected by bringing about a change in the opposite (negative)
direction. Put another way, if there is too much of a particular factor, a process is set
in motion to reduce that factor; if there is too little, a process is set in motion to
increase that factor.
Homeostatic control mechanism

A negative feedback system is made up of:
 a receptor that detects a change (deviation) from the set point and sends
information to the control centre, usually the brain.
 a control centre that processes the information and activates corrective
mechanisms that it send to the effector.
 an effector that responds and corrects the change, returning conditions to the
set point.
If for any reason homeostasis cannot be maintained illness or even death can result.
Negative feedback system
Examples of negative feedback by hormones
1. Glucose (blood sugar) concentration in blood See page 43.

2. Reproductive hormones See page 102.
4. Pancreas
The pancreas is an unusual gland as it functions as both an exocrine gland and an
endocrine gland.
 The exocrine function is the secretion of pancreatic juice, which flows along
the pancreatic duct into the duodenum where it helps in chemical digestion.
 The endocrine function is the secretion of hormones by groups of cells
called islets of Langerhans. These are scattered throughout the pancreas.
The hormones they secrete pass directly into the blood.
85
Secretions from the pancreas
Islets of Langerhans hormones

There are two types of cells in the islets that secrete two different hormones.
 Alpha cells secrete glucagon

 Beta cells secrete insulin
The structure of pancreatic tissue
86
Micrograph of pancreatic tissue
Functions of these hormones

Both hormones play a role in controlling the level of blood sugar / glucose in the
blood.
In a healthy human, normal glucose concentration is between 3.5 and 5.5 mmol/litre
of blood.
Glucose, a simple sugar derived from digesting the carbohydrates that are eaten, is
a source of cellular energy. It is transported throughout the body in the bloodstream
and cannot enter the cells without the aid of insulin.
 Insulin, therefore, will lower blood sugar (glucose) level.

 Glucagon raises blood sugar level.
Insulin and glucagon therefore have antagonistic (opposite) effects.
How insulin lowers blood sugar levels
87
 After a meal containing carbohydrates, glucose from the digested food, is
absorbed from the small intestine and moves into the blood. This
will increase blood glucose levels above the normal set point, i.e. there is a
change from the norm. As this blood passes through the pancreas, the beta
cells detect the raised glucose levels and respond by secreting insulin into
the blood.
 Insulin goes to the main target organs, the liver and muscles, where it:
–makes the cell membranes more permeable to glucose, which enables more
glucose to leave the blood and enter the cells.
–increases the rate at which glucose is converted into glycogen in the cells.
 As the above processes take glucose out of the blood the blood sugar levels
are lowered.
 The lower glucose level is detected by the insulin secreting cells which then
stop releasing insulin into the blood.
This is another example of negative feedback control mechanism – the receptor

organ is the pancreas and the effector is the liver (and muscles).
Diagram showing the homeostatic control of blood sugar (glucose)
Learning activity 3
Homeostatic control of glucose

Question 1
By referring to the diagram below complete the questions that follow. The large, bold
numbers in the questions relate to the numbers in the diagram.
Enjoy doing this exercise.
1.The set point or normal level of glucose, 1, in the blood is ____________

mmol/litre. (1)
2.Why has the glucose level increased at 2? (1)

________________________________
3.The blood passes through the control centre, the 3 ________________. In this
gland a group of endocrine cells, 4, the ____________________________, are
stimulated, by the change in blood sugar level, to secrete the
hormone, 5 ___________. (3)
4.This hormone travels in the blood stream to its two main target (or effector) organs
(A + B), namely __________ and _________. (2)
88
5.What effect does this hormone have at 6? (1)
6.As a result of the hormone’s influence in target organs, A and B, what has
happened to the blood sugar level at 8? (1)
7.Using one word, describe what effect insulin has on the level of glucose in the
blood. (1)
[10
Question 2
The following graph shows the variations in glucose and insulin levels in the blood of
a healthy person over a ten-hour period. The normal level (set point) of glucose in
the blood is 100 units (3.5 to 5.5 mmol/litre blood). Two meals and a period of
exercise were taken at the times shown on the graphs.
1.1.What effect does a meal have on the blood glucose level? (1)
1.2.Explain your answer. (2)
2.What proof is there (on the graph) that insulin causes a decrease in the blood
glucose level? (2)
3.Explain why the insulin level begins to increase at point A on the graph. (2)
4.1How long after a meal does it take for the blood glucose level to return to normal?
(1)
89
4.2Suggest a possible reason for your answer. (2)
[10]
Total [20]
Are you finding graphs easier now? Be confident in your approach as they
provide so much information.
Be confident
How glucagon increases blood glucose

When waking up in the morning or after exercise, the glucose level in the blood is
low.
When waking up in the morning, glucose level is low
 As this blood passes through the pancreas, the glucagon secreting cells
(alpha cells) detect the low glucose levels and respond by
secreting glucagon into the blood.
 The target cells are the liver cells (not the muscle cells) where the glucagon
causes the breakdown of stored glycogen into glucose.
 As a result, the liver releases glucose into the blood increasing the blood
glucose level.
 The increased glucose level is detected by the glucagon secreting cells, which
then stop releasing glucagon into the blood.
Yet another example of negative feedback control system.
Diabetes (Diabetes mellitus)

Diabetes is a chronic disease characterised by high levels of glucose in the blood.
In South Africa about six million people suffer from this disease. Of these 90% are
adults and 10% are children. There are several forms of diabetes but Type
1 and Type 2 are the most common.
Type 1 diabetes (insulin dependent)

Type 1 diabetes usually starts in childhood and accounts for 5 to 10% of all
diagnosed cases.
The initial symptoms are:
 tiredness
 production of large quantities of dilute urine containing glucose. The kidneys
cannot reabsorb all the extra glucose from the renal tubules.
 great thirst due to loss of so much liquid.
90
What causes Type 1 diabetes?
This is an auto-immune disease as the body’s immune system destroys the insulin-
producing beta cells in the pancreas.
As a result the pancreas does not make insulin. Glucose therefore remains in the
blood instead of moving into the cells. This condition is known as hyperglaecemia.
hyper = high level; glaecemia = sugar
How can Type 1 diabetes be treated?

It is a life-long disease for which, as yet, there is no cure. If, however, the patient is
highly disciplined and responsible, with proper diabetic management and regular
exercise, the disease can be controlled.
 As little or no insulin is being produced, the most important treatment is

following a routine of daily injections of insulin.
 It is important for the diabetic to test his/her blood sugar levels
frequently with a finger-prick test so that the correct amount of insulin can be
injected.
Measuring the glucose level in blood with a finger prick test
The short term effects of not following this routine are extreme thirst, nausea,
vomiting, dehydration, dizziness and a coma.
The long-term goals of treatment are to prolong life, reduce symptoms and prevent
diabetes-related complications such as blindness, kidney failure, amputation of limbs
and increased risk of heart attack and stroke.
Future cures on the horizon include pancreas transplants, and use of stem cells to
produce new functional beta cells.
Type 2 diabetes (non-insulin dependent)

Type 2 diabetes usually starts in adulthood and is directly influenced by lifestyle.
However it is becoming more common in children.
It is much more common than Type 1, accounting for 90 to 95% of all diabetes
cases.
What causes Type 2 diabetes?

Type diabetes develops when the body produces less insulin or is not able to use
the insulin correctly. This may be due to faulty insulin receptors on the cells that
normally aid in the transport of glucose into body cells – a condition known
as insulin resistance.
What are the warning signs for the onset of diabetes?

Symptoms tend to develop more gradually than in Type 1. Therefore many people
are unaware of having the disease.
91
Increased thirst, frequent urination, blurred vision, tingling or numbness in hands or
feet, frequent infections and slow-healing wounds are common symptoms of Type 2
diabetes.
As South Africa has a very high level of diabetes it is important for everyone to be
aware of these symptoms. Obese women are more prone to developing diabetes
than obese men. With 40% of the female population classified as obese or
overweight, the prediction that every second or third woman in South Africa will
suffer from diabetes by 2025 is not unrealistic.
What factors increase the chance of developing Type 2?

The following all play a role in developing insulin resistance and increasing the risk of
Type 2 diabetes:
 a diet high in carbohydrates (starches and sugars), fast foods (‘junk foods’)
and over processed food leading to overweight and obesity. This is the cause
of 87 % of Type 2 diabetes.
 lack of exercise
 increasing age
How can Type 2 be treated?
 There is a lot of evidence that following a diet that is high in fats and low in
carbohydrates can vastly improve and possibly even reverse this
condition. Out with junk food!
 Losing weight and regular exercise are also very important.
 In some cases, oral drugs or insulin are given.
Note:
There is global concern amongst health care workers that more and more children
and teenagers are being diagnosed with the disease. This is probably due to a
sedentary lifestyle and poor eating habits, causing the young to become overweight.
Learning activity 4
Diabetes
1.What hormone is lacking or not working efficiently in diabetic sufferers? (1)
2.Give two common symptoms of diabetes. (2)
3.Mention three causes of Type 2 diabetes? (3)
4.Apart from very poor eating habits why are more and more children suffering from
Type 2 diabetes? (2)
5.What do the following terms mean?
5.1hyperglycemia
5.2hypoglycemia (2)
Total [10]
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DBE 2017 NOVEMBER
5. Adrenal glands
A pyramid-shaped adrenal gland is found on the top end of each kidney. Each
adrenal gland is made up of two glands, the inner medulla and outer cortex.
a. Adrenal cortex
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The adrenal cortex secretes a group of steroid (fat - based) hormones, i.e.
aldosterone, cortisone and reproductive hormones. Their functions are varied but
very important.
1.Aldosterone
Aldosterone causes increased reabsorption of sodium ions from the filtrate in the
kidney nephrons and the simultaneous movement of potassium ions into the filtrate.
It therefore helps to regulate the electrolytic levels of body fluids and is therefore vital
for osmoregulation.
2.Cortisol
Cortisol (cortisone) increases the body’s ability to resist stress of all kinds. It is
also anti-inflammatory and anti-allergic.
b. Adrenal medulla
The medulla secretes one of the best-known hormones, adrenalin.
What are the effects of adrenalin?

Adrenalin, the ‘fight or flight’ hormone, is secreted under situations of sudden
danger or excitement and will prepare the body for action so it can cope with the
emergency.
Adrenalin excreted
Adrenalin causes the same effects as the sympathetic nervous system to bring about
the following effects:
1. Blood pressure is increased because vasoconstriction (narrowing of blood

vessels) takes place in the skin and alimentary canal. This enables more
blood to go to the skeletal and cardiac muscle where it is needed.
2. The blood sugar levels are increased because liver glycogen is converted to
glucose. The glucose is released into the blood stream and will provide fuel
for the release of extra energy.
3. The oxygen content of the blood is raised because the breathing rate and
depth of breathing is increased. ‘Rate’ because breathing muscles are
stimulated and ‘depth’ because the bronchial tubes dilate. The extra oxygen is
needed for increased respiration which results in more energy being released.
4. The heart rate is increased. This results in more blood with higher levels of
glucose and oxygen going to the muscles. Cellular respiration therefore
increases in the muscle cells and more energy is made available for muscle
activity.
5. Skeletal muscle-tone is increased enabling the muscles to respond more
quickly.
The above five are the most significant effects. You must know them.
Adrenalin has many other effects which include the following.
 Dilation of pupils for better vision in the emergency.

94
 Increased sweating for increased cooling of the body when being physically
active.
 Reduction of digestive system activity.
 Increased mental alertness to be aware and think about how to cope with the
emergency.
Learning activity 5
Adrenalin
Remember adrenalin works in ‘sympathy’ with the sympathetic nervous system,

i.e. they have the same effects on the body
Question 1
1.From which gland and under what conditions will adrenalin be released?
__________________
___________________________________________________________________
__ (3)
2.Which part of the nervous system will have the same effect as adrenalin?
___________________ (1)
3.Complete the following table: 1 mark for each item under ‘Effects’ and 2 marks
each for ‘Value of change’.
Feature Effects Value of change
3.1heart rate and volume
3.2blood vessels in the skin and gut
3.3rate and depth of breathing
3.4blood vessels in the voluntary muscles
3.5bronchial tubes
3.6pupils of the eye
3.7peristaltic action in the gut
3.8sweat glands
(24)
4.1Adrenalin causes which compound to release glucose? (1)

_______________________
4.2In which organ of the body does this reaction occur? (1)
________________________
4.3Why is this extra glucose needed? (2)
95
5.Adrenalin causes an increase in muscle tone. How does this help to cope with an
emergency? (1)
6.Why would a coach not be worried if a soccer player said he was very nervous and
excited just before an important match? (2)
[35]
Question 2
The following graph shows the changes in the blood sugar level in a normal, healthy
person over a period of 160 minutes. During this time the person was given an
injection of adrenalin.
1.After how many minutes was the adrenalin injection given? (1)
__________________
2.Name the hormone responsible for the slight increase in the blood sugar level at E
and G. (1)
3.Name the hormone responsible for the decrease in the blood sugar level between
points C and D. (1)
4.Which cells of which gland secrete the hormone mentioned in 4? (2)
[5]
Total [40]
6. Gonads (reproductive organs)

The gonads are the testis in males and the ovaries in females. Apart from producing
gametes (sex cells) these organs secrete large quantities of sex hormones.
Ovaries
The ovaries secrete oestrogen and progesterone.
What are the functions of oestrogen?

1.Oestrogen on its own is responsible for the:
 rapid increase in the rate of physical growth during puberty.

 appearance of the secondary sex characteristics of females at puberty.
 maturation of the reproductive organs and keeping them in a functional state.
2.Oestrogen together with progesterone, promotes cyclic changes in the

endometrium during the menstrual cycle, i.e. it prepares the endometrium for
pregnancy. It becomes more glandular and vascular and the cells become swollen
with nutrients.
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Increased oestrogen levels inhibit the release of FSH and LH. This is the basis of
some of the birth control tablets. With no FSH no egg matures, therefore no
pregnancy can occur.
Learning activity 6
Oestrogen functions
Oestrogen has many functions, but those mentioned are the main ones. Do a simple
diagram to help you remember them.
What are the functions of progesterone?
1. Progesterone, together with oestrogen, promotes cyclic changes in the

endometrium preparing it for pregnancy.
2. During pregnancy it helps maintain the endometrium in a functional state.
3. During pregnancy progesterone helps to keep the smooth muscle of the
uterus wall relaxed.
Testis
The testis secrete the hormone, testosterone.
What are the functions of testosterone?

Testosterone is responsible for the following.
1. Rapid increase in the rate of physical growth during puberty.

2. Development of the secondary sex characteristics of males at puberty.
3. Maturation of the reproductive organs and maintaining them in a functional
state.
4. Sex drive.
Learning activity 7
Hormones of the reproductive organs

1.What is the general term for the testis and ovaries? (1)
_______________________
2.Name the hormone secreted by the testis. (1)
3.Name the hormone that stimulates the testis to secrete the hormone named in 2.
(1)
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4.Which hormone stimulates the ovary to secrete oestrogen? (1)
______________________
5.What other female hormone does the ovary secrete? (1)

_______________________
6.Name the hormone that is responsible for the maturation of the reproductive
organs in:
6.1females, and _______________________
6.2males (2) _________________________
7.What hormone keeps a woman’s body in a pregnant state? (1)

__________________
Total [8]
Learning activity 8
General endocrine questions

1.How do hormones reach their destinations? (1)
2.The diagram below shows the position of some of the endocrine glands. Answer
the questions that follow.
Position of some endocrine glands
2.1Gland numbered 1 is sometimes called the hypophysis. What is its more common
name? (1)
2.2One of the hormones it secretes is growth hormone. Name two types of body
tissue that will be affected by this hormone. (2)
2.3Name gland numbered 2 and the hormone it secretes. (2)
2.4What micronutrient is needed to make the above mentioned hormone? (1)
2.5What effect has this hormone on the metabolic rate in our cells? (1)
_________________
2.6Name the group of cells in the pancreas, number 3, that secrete hormones. (1)
2.7Name the two hormones the cells, mentioned in 2.6, secrete. (2)
2.8What disease will result from the beta cells failing to secrete their hormone? (1)
2.9What organic substance in the blood is affected by the level of these two
hormones? (1)
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2.10Name the hormone from gland 1 with the kidney as a target organ. (1)
2.11What is its function? (1)
3.Study the flow chart below and answer the questions that follow.
3.1Name hormone 3. (1) ________________
3.2Name gland 1 in this flow chart. (1)
3.3What effect does an excess of hormone 2 have on hormone 3? (1)
3.4Provide a term for this effect. (1)
Total [20]
Use of hormones in sport
There is widespread use of hormones in all levels sport. The hormones include
human growth hormone, anabolic steroids and erythropoietin.
Growth hormone
Over a period of 20 years, it appears that abuse of growth hormone (HG) is present
in all levels of sport. This is partly due to the fact that GH is more difficult to detect
than most other performance enhancing drugs, such as anabolic steroids.
Claims that growth hormone enhances physical performance are not supported by
the scientific literature, although the perception that it does is common among sports
people.
Anabolic steroids
Anabolic steroids are controversial in the sports world because of the health risks
associated with them and their unproven performance benefits. Most are illegal and
are banned by professional sports organisations and medical associations.
If an athlete is caught using steroids, his or her career can be destroyed. Being a
star athlete means training the healthy way: eating the right foods, practicing and
strength training without the use of drugs.
Anabolic steroids are a common term for male hormones (testosterone) and female
hormones (oestrogen and progesterone). Besides making muscles bigger, anabolic
steroids may help athletes recover from a hard workout more quickly by reducing the
muscle damage that occurs during the training session. This enables athletes to
work out harder and more frequently. In addition, some athletes may like the
aggressive feelings they get when they take the drugs.
 Testosterone and Androgenic Anabolic Steroids (AASs - these are

specialised derivatives of the male hormone testosterone). They increase
protein synthesis and can increase lean muscle mass. These are still the
drugs chosen by modern-day cheaters and cheating nations.
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Anabolic steroid abuse has serious side effects.
–Men may develop prominent breasts, baldness, shrunken testicles, infertility

and impotence.
–Women may develop a deeper voice, enlarged clitoris, increased body hair,
baldness and infrequent or absent periods.
–Both men and women might experience severe acne, liver abnormalities and
tumours, increased risk of tendinitis and tendon rupture, high blood pressure
(hypertension), heart and circulatory problems, aggressive behaviours, rage
or violence, psychiatric disorders, such as depression and inhibited growth
and development in teenagers
 Female hormones also have anabolic effects, although not as marked as

male hormones.
–Athletes who return to training after pregnancy (with its high levels of female
hormones) often find that they are stronger than they were before.
–Oral contraceptives are permitted substances and may well be desirable.

They tend to reduce menstrual loss and therefore there is less chance of an
iron deficiency.
As well as making menstruation more tolerable, they can be used to adjust its
timing so that the competitor is not premenstrual or menstruating during an
important event.
Erythropoietin (EPO)
EPO is a naturally occurring hormone produced in the kidney to regulate red blood
cell formation. Introduced EPO increases red blood cell production to unnatural
levels. The increase improves the oxygen-carrying capacity of the blood. Some
reports claim an up to a 15% improvement in endurance performance in sporting
activities.
Introduced EPO is not easy to detect in the body as it only lasts in the body for a
short time, up to 24 hours.
EPO abuse is very dangerous as it ‘thickens’ blood, which can cause strokes and
heart attacks.
Some other hormones that are used
 Human chorionic gonadotrophin (hCG) and luteinising hormone (LH) –

increases the body’s production of testosterone.
 Insulin – works with GH to control blood glucose.
The value of cortisol and/or adrenalin during sporting action

Both adrenalin and cortisol (cortisone), natural hormones of the body, are very
important in preparing sports people for sporting or athletic action.
 Adrenalin increases heart rate, force of muscle contraction and respiration. It

also stimulates the central nervous system making the mind more alert. The
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body begins to sweat more, in preparation to cool the muscles and the pupils
dilate in an effort to take in more of the surroundings.
 Cortisol increases glucose levels in the blood making it available for muscles
to use, which increase the release of energy. It also temporarily inhibits other
systems of the body, such as digestion, growth and the immune system – so
saving energy for physical activity.
Cortisol has a catabolic (breakdown) effect on muscle tissue, which for sportspeople
is undesirable. The muscles are able to recover if the body is rested after training.
However, sportspeople often over-train and their cortisol level becomes chronically
elevated. Performance will therefore be negatively affected as the muscles cannot
recover properly. To reduce cortisol levels plenty of rest between workouts is vital.
Stress system
We are all subjected to some sort of stress each day be it at school, work, in social
situations, and even at home. Our stress system relies on two key
hormones: adrenalin and cortisol.
When stressed adrenalin will work first – getting the body ready for action. Shortly
after adrenalin is released cortisol is released, it works for a long time keeping the
body in a state of action.
The following graph shows that just as your levels of adrenalin start coming down, so
the amount of cortisol flowing through your blood rises.
Moreover, the effect of cortisol lasts longer than adrenalin, which means that even
though it builds up slowly, it also takes a long time to go back to normal in your body.
And should you constantly be subjected to stressful activities or situations, which
require regular inputs of adrenalin, your levels of cortisol slowly increase.
The relationship between adrenaline and cortisol
The rise in cortisol has negative effects on the body, which include:
weakened activity of the immune system, which means we can become ill.
reduced bone formation, which can lead in the long-term to osteoporosis

(progressive bone disease), in both men and women.
reduced production of protein.
reduced ability to remember information that had been stored.
The latter effect is certainly not good for matric learners!
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Learning activity 9
Short questions
1. Multiple choice
alternative and write it below the relevant number in the table below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
1.Which one of the following statements concerning hormones is incorrect?

(a) They can be effective over a long period of time.
(b) All hormones are organic compounds. (c) Hormones are carried by the blood
stream to the target organs.
(d) Hormones are products of endocrine glands.

Questions 2 and 3 refer to the diagram below.
2.Which one of the following secretes a hormone under conditions of anxiety and
emergencies?
(a) 1; (b) 2; (c) 4; (d) 5.
3.The thyroid stimulating hormone (TSH) is secreted by: (a) 5; (b) 4; (c) 2; (d) 1.
4.The basic metabolic rate of the human body is determined mainly by the: (a) lungs;
(b) heart; (c) thyroid gland; (d) cerebellum.
5.The hormone that has the same effect on the body as stimulation by the
sympathetic nervous system, is: (a) cortisone; (b) thyroxine; (c) insulin; (d) adrenalin.
6.Which of the following hormones function antagonistically as regards the effect

they have on their target organ? (a) insulin and glucagon; (b) TSH and thyroxin; (c)
cortisone and aldosterone; (d) cortisone and adrenalin.
7.Which statement is incorrect in connection with adrenalin? (a) Is produced in the

medulla of the adrenal gland. (b) Strengthens the contraction of the heart. (c)
Accelerates the conversion of glucose to glycogen. (d) Causes an increase in blood
pressure.
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8.If a lot of carbohydrates are eaten, the secretion of insulin results in: (a) lower
blood sugar levels. (b) increased cell utilisation of glucose. (c) storage of glycogen.
(d) all of these.
9.Absence of thyroxin would result in: (a) high metabolic rate; (b) depression of the
CNS and lethargy; (c) hyperthyroidism; (d) increased heart rate and force of
contraction.
Questions 10 to 12 are based on the accompanying graph which shows the

concentration of glucose as well as certain hormones in the blood over a period of
time. During this time the person suffered a sudden fright.
10.It can be deduced from the graph that:

(a) The blood glucose level influences the level of hormone 2. (b) The person
became unconscious at point M on the time scale. (c) An increase in the level of
hormone 2 causes the level of glucose in the blood to increase. (d) The blood
glucose level is directly influenced by hormone 1.
11.Hormone 1 represents: (a) adrenalin; (b) thyroxin; (c) glucagon; (d) insulin.
12.A person’s pupils will return to normal size at approximately which point on the
time scale?
(a) M; (b) N; (c) O; (d) P. Think!
13.Which one of the following would not be true if a patient’s pancreas was surgically
removed?
(a) The glucose level in the blood would increase. (b) The glycogen level in the liver
would decrease. (c) The insulin level in the blood would decrease. (d) The glycogen
level in the blood would increase.
14.Which of the following statements is not true of Type 1 diabetes? (a) It occurs in
children and young adults. (b) It is incurable. (c) It accounts for 90 to 95% of diabetic
cases. (d) Treatment involves regular injections of insulin.
15.Which of the following is true of the hormone oestrogen? (a) It stimulates

ovulation; (b) It is secreted by pituitary. (c) It is partly responsible for cyclic changes
in the endometrium. (d) It is secreted by the adrenals.
[15]
2. Mix and match
Match each description in Column A with an item in Column B. Write the letter next
to the relevant number.
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Column A Ans Column B
1. Secreted by the pancreas when blood glucose A. anti-diuretic

level is high hormone
2. Secreted by the pancreas when blood glucose B. growth hormone

level is low (STH)
3. Causes the kidneys to conserve water C. oestrogen
4. Anabolic hormone affecting muscle and bone D. insulin

development
5. Secondary sex characteristics of females at E. glucagon

puberty
[5]
3. True or false statements
In each case, write down if the statement is true or false. If false, write down the
incorrect and correct words.
Statement T/F Incorrect Correct

word word
1. Adrenalin causes the constriction of the

bronchioles.
2. Aldosterone controls the salt concentration of

blood.
3. If there is too little glucose in the blood a person

could be suffering from diabetes mellitus.
4. An enlarged thyroid could result from a sodium

deficiency.
5. The hormone STH (somatotropin) causes

ovulation.
[5]
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Each of the following questions consists of two items in the first column (numbered 1
and 2) and a statement in the second column. Consider which item(s) relate to the
statement.
A if only item A relates to the statement
B if only item B relates to the statement
C if both items A and B relate to the statement
D if neither item A or B relate to the statement
Column A Column B Answer
1. 1. hormones Secretions of ductless glands

2. enzymes
2. 1. exocrine gland Pancreas

2. endocrine gland
3. 1. eating too many carbohydrates Primary cause(s) of Type 2

2. eating too much processed diabetes
food
4. 1. growth hormone Controls metabolic rate

2. thyroxin
5. 1. Type 1 diabetes Insulin dependent

2. Type 2 diabetes
[5]
5. Terms
Write down the correct word or term for each of the following.
1.The endocrine gland that controls the hormone secretions of most other
glands.
2.A disorder in which the hormone control of blood glucose is defective

because of a lack of or malfunctioning of insulin.
3.The part of the adrenal gland which secretes the hormone adrenalin.
4.The hormone produced in the hypothalamus which makes collecting and
105
distal convoluted tubules more permeable to water.
5.The hormone that controls the development of the secondary sexual

characteristic in males.
[5]
Total [35]
2.2 Reproduction in flowering plants
Reproduction is the ability of organisms to produce a new generation of

themselves. It is extremely important for the survival and evolution of a species
because through reproduction, an individual passes on its genes to the next
generation.
There are two natural types of reproduction:
Asexual – production of a new generation of the same species by one parent
Sexual – production of a new generation of the same species by bringing together

the genetic material of two parents.
Plants die of old age, disease and from being eaten by other organisms. New plants
need to be produced to replace those that die.
What is the similarity between asexual and sexual reproduction?
While there are large differences between the two processes they do have in
common that both processes:
produce the same kind of organisms in order to prevent their species from dying out
and becoming extinct.
result in food being produced, which is vital to feed the world’s growing population.
What are the differences between asexual and sexual reproduction?
Characteristics Asexual reproduction Sexual reproduction
Number of One, i.e. all individuals can Two, with two genders
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parents produce offspring
Processes One stage, i.e. mitosis with Two stages, i.e. meiosis and
no fusion of cells, therefore is fertilisation with fusion of two
quicker cells, therefore is slower
Gamete formation No gametes formed Gametes formed
End result Offspring are genetically Offspring are genetically

identical to the parent, i.e. different to parents, i.e. there
there is no variation because is variation because alleles
alleles are not shuffled are shuffled during:
meiosis, when gametes are

formed
fertilisation, when alleles are

joined in new combinations
Value In unchanging (stable) In changing (unstable)

environment, well adapted environment, individuals with
individuals are preserved variations can adapt to new
conditions
Reproduction is possible
where there are no or few
mates
Rate of Faster – all individuals can Slower process – half

reproduction reproduce offspring population are males who do
not produce offspring
Energy input More efficient, no energy input Less efficient, energy input is
needed needed to produce gametes,
and find and court a mate
Outside agents None needed Pollinators often necessary

for pollination
Ability to adapt to No Yes

environment
Possibility of Low – usually no genotype Good – genotype variation

evolution variation
What are the advantages of asexual reproduction?
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The advantages of asexual reproduction include the following:
All individuals can produce offspring therefore there is no expenditure of energy to

produce gametes or find a mate.
The process is simple and fast as it involves only mitosis, e.g. a single bacterium
by dividing into two every 20 minutes can produce 16 million bacteria in 8 hours.
It is very useful in unchanging (stable) conditions, i.e. if the parent is well

adapted to a particular environment the genetically identical offspring will also be
well adapted.
A favourable mutation can spread rapidly enabling the population to adapt quickly
to new environmental conditions, e.g. resistance to antibiotics and insecticides.
What are the disadvantages of asexual reproduction?
Unless there is a mutation, there is no variation in the offspring as there is no

recombination of alleles. If the environment changes the population might be unable
to adapt to the new conditions and could die out.
Overcrowding may occur and resources such as food might be in short supply.
Learning activity 1
Advantages and disadvantages of asexual reproduction
Devise a simple mind map or learning diagram to show each topic.
What is the advantage of sexual reproduction?
Sexual reproduction results in variation which:
is the basis of evolution.
gives organisms a better chance of survival in an unstable environment as the

offspring may be able to adapt to the new conditions.
may prevent the spread of disease as the offspring might be genetically resistant to a
particular disease.
may reduce the chance of inheriting a disease from a parent.

108
What are the disadvantages of sexual reproduction?
There is a high expenditure of energy as in plants special organs of reproduction

need to be produced, i.e. flowers.
The reproduction process is slower than asexual reproduction as it takes time for
gamete production and the meeting of gametes.
Unfavourable mutations and recessive genes might be expressed in the

offspring.
Outside agents may be needed in plants to carry pollen or seeds.
Learning activity 2
Advantages and disadvantages of sexual reproduction
Devise a simple mind map or learning diagram to show each topic.
Advantages
Disadvantages
How does sexual reproduction take place?
Sexual reproduction is much more complicated than asexual reproduction.
The diploid parent produces gametes (sex cells) in the gonads (sex organs) by
meiosis. The gametes are haploid as they contain one set (n) or half the number of
chromosomes.
The male and female gametes are brought together by pollination (plants)
or mating (animals).
The gamete nuclei then fuse, a process known as fertilisation.

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The new cell, the zygote, is diploid (2n) as it has two sets of chromosomes.
The zygote grows by mitotic cell division into a new individual.
The gametes
The female gamete is quite large and not motile while the male gamete is small, and
motile in animals.
In animals, the male gamete is known as a sperm and the female, an egg or ovum
In many plants, the male gamete is just a nucleus in a pollen grain while the female
gamete is an egg cell (ovum) in an embryo sac.
Sexual reproduction
Learning activity 3
Asexual and sexual reproduction
Question 1
Match each of the following terms with one of the descriptions (1 to 10). Write the
answer next to the relevant number:
gamete – egg/ovum – sperm – fertilisation – hermaphrodite – zygote – gonads –

meiosis – genetic variation – pollination / mating
1.produce gametes 6.female sex cell
2.male sex cell 7.bringing together of male and female

gametes
3.organism that produces male and
female sex cells 8.sexual reproduction
4.reduces chromosome number 9.biological name for a sex cell
5.joining of male and female sex cell 10.fertilized egg
1 2
3 4
5 6
7 8
9 10
[10]
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Question 2
Which of the following statements about asexual reproduction are false (F) and
which are true (T)? If false, write down the incorrect term followed by the correct
term.
1.It gives rise to large numbers of genetically non-identical individuals.
2.It is slower than sexual reproduction.
3.It allows harmful mutations to be passed on.
4.It is advantageous in changing conditions.
5.It allows a species to multiply quickly and can prevent another species from taking
over.
6.It will allow adaptation to a new environment in the next generation.
7.It is simple as special reproductive cells and structures do not have to be made.
T/F Incorrect word / correct word
1.
2.
3.
4.
5.
6.
7.
[11]
Question 3
1.If mitosis were the only kind of cell reproduction, how might the world be different?
(2 x 2)
2.Why sexual reproduction appeared and is so prevalent is a major puzzle in modern

biology. Why does sexual reproduction need more energy than asexual
reproduction? (5)
[9]
Total [30]
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Angiosperm reproduction
What is an angiosperm?
Most of the plants you see growing around you are angiosperms. They are plants
with flowers which produce their ovules enclosed in an ovary, not naked on a
cone scale, as in the gymnosperms, eg pines.
Angiosperms grow in almost every habitat, except the open ocean, where the algae
are found. This is unlike the mosses and ferns which need to grow in damp habitats.
What is a flower?
The flower is the organ of sexual reproduction. It contains the reproductive

organs and often will attract pollinators.
Many flowers make both male and female gametes. These are said to
be hermaphrodite (bisexual).
The male gametes are found inside the pollen grains which are produced by
the anthers.
The female gametes are inside the ovules which are found enclosed by the ovary.
What is the structure of a flower?
The parts of the flower probably evolved from specialised leaves, like the cone
scales of gymnosperms. While flowers are very different to each other they all have
certain basic features.
A typical flower consists of a series of modified leaves arranged in four whorls or

circles – the calyx (often green), corolla (often coloured), stamens (male whorl)
and carpels (female whorl). The diagram below shows these four whorls and gives
the general function of each.
112
Flower Parts
Much of this information you will have learnt many years ago!
There are many variations of this four-whorl arrangement – in colour, size and
shape. This diversity can be related to the way pollen is transferred.
Structure of a generalised flower with functions of the parts
Learning activity 4
Flower structure
Supply labels for the diagram below of a section through a flower.
Generalised dicotyledonous flower structure
Total [9]
Male and female parts of a flower

Female part: the carpel
The carpel consists of an ovary, style and stigma.
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The ovary, the main part of the carpel, contains the ovule/s.
* Each mature ovule contains a female gamete.
* Once the female gamete in the ovule is fertilized by the male gamete the:
➢ovule develops into a seed
➢ovary develops into a fruit.
The style is the slender section connecting the stigma to the ovary. The pollen tube
carrying the male gamete grows along the style towards the ovary.
The stigma is sticky and is the part that receives pollen. ‘Sticky stigma’ – fairly
similar sounds!
Male part: the stamen
The stamen consists of the anther and filament.
The anther is the structure that forms pollen grains in which the male gametes are
found.
The names of the floral parts can be quite confusing; the following ideas might
make it easier for you to remember them.
Male parts, each word has ‘man’ or ‘men’ in it:-

stamen
(m)anther
filament
Female parts:-
stigma – ‘ma’ – a term for a female parent
style – what every woman wants to have
ovary – female humans have ovaries as well
What is the difference between pollination and fertilisation?

Pollination
Pollination is the transfer of pollen from an anther to a stigma, thereby enabling

fertilisation and reproduction.
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When the anther is mature it splits open and discharges the pollen. The pollen is
then carried to the stigma by various natural means, the most common being wind
and insects. In plant breeding, pollination is carefully controlled by humans.
There are two kinds of pollen transfer – cross-pollination and self- pollination.
In cross-pollination the pollen is transferred from the anther of a flower of one plant
to the stigma of a flower of another plant, of the same species. This type of
pollination will result in genetic variation in the offspring.
In self-pollination the pollen is transferred from the anther to the stigma of the same
flower or to another flower on the same plant. This type of pollination will not result in
genetic variation in the offspring.
Diagram to show self (top arrow) and cross (bottom arrow) pollination
How can self-pollination be prevented?
In nature the following means prevent self-pollination.
–In bisexual flowers the anthers and stigmas ripen at different times. Most commonly
the anthers ripen first.
–Flowers are unisexual, they therefore cannot pollinate themselves.
–The stigma is positioned above the anthers.
Plant breeders will remove anthers to prevent self-pollination.
Fertilisation
Fertilisation is the joining of two haploid cells, the male gamete and female
gamete, to form a diploid zygote. The zygote develops by mitosis into the adult plant.
In flowering plants fertilisation take place after pollination.
After the pollen grain lands on the stigma it develops a pollen tube which grows
along the style and into the ovule. The pollen tube carries the male gamete. Once
the gamete enters the ovule fertilisation can occur.
After fertilisation the development of the embryo and the seed can begin.
Pollination followed by fertilisation
How a seed is formed
After fertilisation:
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the zygote divides numerous times by mitosis and develops into an embryo
consisting of:
–cotyledons or seed leaves. The cotyledons often take food from the parent plant
which they store for future use.
–a radical (embryonic root)
–a plumule (embryonic shoot).
the rest of the ovule develops into endosperm tissue. This is the stored food, e.g.
starch, protein or oil.
the outer covering of the ovule thickens and hardens, forming the seed coat or
testa. It saves the seed from being damaged as well as preventing the entry of
bacteria and fungi.
How a fruit is formed
While a seed is being formed the ovary is also growing. It is now called a fruit. Fruit
formation happens in different ways in different plants.
Functions of fruits
They contain and protect the seeds.
Fruits help to disperse the seeds from the parent plant.
One function of friut
How asexual/sexual reproduction historically has lead to improved food crops
Of the approximate 75 000 species of edible plants 7 000 are used for food by
humans. Humans have domesticated wild plants for their use for the last 9 000 to
11 000 years.
Domestication lead to:
great phenotypic changes (and altered genotypes) resulting in vastly improved food
crops.
new varieties developing.
Today, all our principal food crops come from domesticated varieties. Most of the
domestication involved cereals, i.e. wheat, maize and rice.
wild plants = plants that grow in nature without the aid of humans. Very few wild
plants are now used as food sources.
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Domestication involved skilful breeding. The breeders used variation that existed in
plant species and also the variation that arose from sexual reproduction to asexually
or sexually improve the food crops further.
How did asexual reproduction improve the crops?
Asexual reproduction covers all those modes of the reproduction of plants where
normal gamete formation and fertilisation does not take place.
Techniques include division, grafting, using storage organs (bulbs, corms, tubers and
rhizomes) and cuttings.
While the basic feature of asexual reproduction is genetic stability with no variation in
the offspring a mutation could have produced a plant with a new superior trait.
For example a crop plant could have produced bigger seeds, fruits or tubers. If these
plants were then reproduced by asexual means more plants with the superior trait
could have been grown.
With repeated selection and elimination of plants without the superior trait the food
crop would eventually have consisted entirely of plants with the superior trait.
In this way the particular crop would have been improved by asexual means.
Grafting is a technique whereby tissues from one plant are inserted into those of
another so that the two sets join together.
–One plant is selected for its roots. This is called the rootstock. Rootstocks with
good traits, e.g. resistance to certain pests and diseases and/or the ability to grow in
difficult soil conditions would have been used.
–The other plant is chosen for its superior fruits (larger and improved yield) and is
called the scion. As the scion contains the superior traits for food production the
mature plant would be more productive. Further scions would be cut from this plant
for further grafting resulting in an overall improved crop.
Diagrams to show the process of grafting
Grafting has been practiced for thousands of years to improve crops, particularly fruit
tree e.g. apples, pears. It is still today used in asexual propagation of certain
commercially grown food crop plants, e.g. grapes and avocado pears.
How did sexual reproduction improve the crops?
Over time breeders also used sexual reproduction to improve their crops. The
plants originating from sexual reproduction were often quite different from their
parents and from each other. Some of these differences were beneficial traits that
117
would improve the food crop. Such traits were larger yield, larger seed, tuber and
fruit size, resistance to pests and/or disease and being able to grow in poorer soil.
Breeders selected and planted seed from the superior plants, while eliminating seed
from those plants with less desirable traits. With repeated selection an improved crop
resulted.
Examples include:
The cross pollination of individuals of a species produced new crop varieties with
improved traits. For example, a mildew-resistant pea may have been crossed with a
high-yielding but mildew-susceptible pea. The purpose of the cross was to introduce
mildew resistance without losing the high-yield traits. Eventually all seed produced
from the favoured plants would have produced plants with the desirable traits. These
plants became known as cultivars.
cultivar – is a plant or grouping of plants selected for desirable characteristics that
can be maintained by propagation.
A crop plant may have shown a new trait, e.g. a larger maize cob with more ‘pips’.
To perpetuate this trait plants grown from this plants seeds were self-
pollinated. The next generation plants would have produced seed with this new trait.
Repeated breeding by self-pollination eventually led to all maize having larger cobs –
a highly desirable feature.
To show how the maize cob historically increased in size due to selective
breeding
Resistance to a particular disease was also been bred into crops species in this way.
Learning activity 5
Historic improvement to crops by asexual and sexual reproduction
Devise two clear learning diagrams to show how through the course of history crop
production has improved by the processes of asexual and sexual reproduction.
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How can plant breeders use asexual reproduction and engineering techniques
to benefit food production and help solve the current food crisis?
The world needs to produce at least 50% more food to feed an estimated 9 billion
people by 2050. However:
climate change could cut crop yields by more than 25%.
land available for crop production is limited, with much of the world's best soils
already in use and others protected, for example, for environmental concerns. The
demand for food brings marginal lands into play for which stress-tolerant crops need
to be developed.
Unless we change how we grow our crops food security—especially for the world’s
poorest—will be at risk.
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To help do this plant breeders can use asexual/vegetative propagation
(some methods were mentioned earlier) and genetic engineering techniques.
Breeders often combine both of these methods.
What are the challenges that future food security pose for plant breeders?
International development agencies believe that breeding new crop varieties is

extremely important for ensuring food security. The new varieties need to be:
even higher-yielding than at present.
resistant to pests and diseases.
drought-resistant or regionally adapted to different environments and growing

conditions.
able to use soil nutrients more efficiently.
How could asexual reproduction benefit future crop production?
Propagation is faster than from seed because there is no gamete formation,

pollination, etc.
All the propagated plants are of a consistent superior quality.
Large quantities of plants can be produced cheaply, easily and quickly, eg by

cuttings. perennating organs, eg bulbs (onions) and tubers (potatoes).
Using the grafting technique fruit trees will grow more quickly to maturity and thus to
fruit production, eg avocado pears.
By micro-propagation (tissue culture) numerous new identical plants (clones) are

produced. Micro-propagation is favoured over traditional crop breeding methods as:
–commercially important crop plants can be mass propagated in a very short period
of time, eg bananas, pineapples, potatoes, date and oil palms, papaya.
–disease-free plants can be produced by selecting disease-free cells and culturing

them in sterile conditions.
–propagation can take place all year independent of seasonal changes.
–it may be used together with genetic engineering to propagate transgenic plants
from genetically modified cells.
tissue culture or micropropagation = a process whereby a small amount of plant

tissue is cultured in a growing medium to produce a callus and then plantlets
callus – a shapeless clump of cells
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Calluses
Learning activity 6
Improvement in crop production
Devise a clear mind map; try to use only pictures, to show how asexual reproduction
is helping to secure food production.
How does genetic engineering benefit crop production?
Genetic engineering is the process of taking a gene out of one organism and put it
into the DNA of another organism.
The resulting plants are known as genetically modified organisms (GMOs, GM

crops, or biotech crops) and the gene that has been transplanted is a transgene.
The production of a new variety with a desired trait in this way is achieved in a much
shorter time compared to conventional breeding.
There are no real interspecies barriers in this type of crop production: all organisms
use the same genetic code, so genes from bacteria, for example, will produce the
correct protein in a maize plant. An important issue to note is that the proteins
produced by transgenes are identical to those produced in the original species,
because the genetic code is universal. However, the signals needed to express
these genes are plant-specific and are not universal. Some modifications must be
made to the signals that control gene expression, since these are more species-
specific. Very technical, but interesting!
A few examples of GMOs:
Bt maize. Bacillus thuringiensis, a soil bacterium, produces a protein that kills many
insect pests, especially the maize earworm. The gene for this protein has been
transplanted into much of the USA’s maize crop giving the maize crop resistance to
that pest.
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Roundup Ready soybeans (plus other crops). Roundup is a brand name for a
herbicide called glyphosate. A bacterial gene that confers resistance to this herbicide
has been transplanted to many crops. The farmer can then spray the fields with
glyphosate and kill virtually all the weeds without harming the crop. About 87% of the
USA’s soybean crop now contains this gene.
herbicide = a chemical that kills herbs/weeds
Note:
As of 2013, roughly 91% of soybeans and about 90% of maize produced in the USA
are genetically modified.
In 2014 about 18 million farmers use GM plants worldwide. Along with the USA and
Canada, emerging economies like Brazil, Argentina, India and China grow them. The
GM crops most commonly grown are soybeans, maize and rape seed (canola).
There is wide scientific agreement that food on the market derived from GM crops
poses no greater risk to human health than conventional food.
What traits are biotechnologists trying to incorporate into food crop plants?
Traits that biotechnologists have and/or are trying to include are:
resistance against certain diseases and herbicides. Disease-resistant rice

and maize is being grown in China as well as virus-resistant sweet potato and maize
in Kenya.
increased tolerance to insect pests. Genetically modified (GM) white maize,

resistant to stalk borer was planted in 2010 in South Africa and yields increased by
up to 60% compared to conventional maize.
nutrient-content enrichment, e.g. additional proteins, vitamins, iron, zinc,

carotenoids can be added.
Golden rice is a new variety of rice containing beta-carotene, a precursor of vitamin
A. The rice will be distributed free to subsistence farmers in areas with a shortage of
dietary vitamin A, a deficiency which is estimated to annually kill 670 000 children
under 5.
increased tolerance of environmental pressures such as salinity, extreme

temperature and drought.
DroughtGard maize is one of the first drought-resistant GM crops and is currently
being planted in the USA.
flood tolerance. A new flood-tolerant rice cultivar (Swarna-Sub1) has been planted
by nearly four million farmers in Asia. One recent study found that farmers in 128
villages on the Bay of Bengal using this rice have increased their yields by more than
25%.
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longer storage life of harvested crops, e.g. strawberries are being targeted by
genetic engineering to extend their shelf life.
improved flavour.
Note:
Most of the genetic engineering has been done on food used in the developed world.
Sadly, little work has been done on food crops favoured by the much of the
developing world, eg millet, cassava or beans. China's scientists are however
working on GM rice, potato and peanuts, crops that have been largely ignored in the
developed world.
It is obvious that combining conventional agricultural practices with modern

biotechnology can enable the achievement of food security for present and future
generations. However, it is important that the performance of a GM crop is closely
studied for several generations and goes through rigorous bio-safety assessments,
before being released for commercial cultivation. GM crops are going to be an
essential part of our life and the enormous potential of biotechnology must be used
to the benefit of humankind.
GMO foods are quite a hot topic. As the growing of GM plants will only increase
it would be a good idea to find out more by looking at good articles on the internet.
You then can develop informed opinions.
Learning activity 7
Genetic engineering and improved crop production
1.In picture form show how genetic engineering of maize and soy is of benefit to
each crop.
2.Using as few words as possible design a diagram to show the existing or hoped for
traits that scientists are trying to incorporate into crops..
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Use of sexual reproduction to produce new and improved varieties of food
crops
To improve food crops breeders can hybridise plants.
Hybrid crops are crops that are produced by cross-pollinating two inbred plants of
dissimilar genotypes.
The seeds from this cross-pollinated plant are hybrid seeds and thus produce a
'hybrid' crop. As the crossing results in genetic variation the hybrid crop could exhibit
new traits some of which could be desirable forming an improved crop or a new
variety. If the plants were left as inbreds this would not have happened. The
breeding of hybrid crops has become extremely popular worldwide in an effort to
improve food crops. It is important to remember that hybrid plants are not genetically
modified.
What improvements have been brought about by hybridisation?
Plants are more vigorous. This could mean that less agricultural land is needed to
produce the same amount of food.
Improved disease resistance - a trait that is constantly sought in plant hybridisation

as diseases affect productivity. For example hybrid tomatoes have resistance
to Fusarium wilt, a very common fungal infection.
Earlier maturity and extended growing season, e.g. tomatoes (there are many
different hybrids), strawberries
Increased yield, e.g. the best rice hybrids showed a 17% yield increase over the
best inbred rice varieties.
Quality improvement, e.g. hybrid watermelons have a crispy taste.
It is evident from this that plant breeding by hybridisation is vital for future agriculture
as it enables farmers to progressively produce improved crop plants.
Learning activity 8
Sexual reproduction and crop improvement
In one diagram show how hybridisation (sexual reproduction) is improving crop

production.
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What is a polyploid plant?
Polyploid plants are those containing more than two homologous sets of
chromosomes, e.g. humans are diploid as they have two sets of homologous
chromosomes. A diploid plant can develop in to a polyploid by:
a disturbance in mitosis or meiosis during crossing of two hybrids.
its seeds being treating with the chemical, colchicine.
Polyploidy is especially common in cultivated plant species. Many genera and

species have their origins in polyploidy. Wheat, for example, after millennia of
hybridisation and modification by humans, has strains that are diploid (two sets of
chromosomes), tetraploid (four sets of chromosomes, e.g. durum wheat), and
hexaploid (six sets of chromosomes, e.g. bread wheat). Many agriculturally important
plants, eg the genus Brassica (cabbage, cauliflower and broccoli) also have many
species that are polyploid.
Advantages of polyploidy in agriculture
Polyploidy forms seedless varieties of fruit such as watermelons, bananas, seedless

grapes and some apples. Why would this be undesirable in wheat?
A wild banana
In the wild, diploid bananas are small and oval with thick tough skin peppered with
large and hard seeds.
These wouldn’t be good to eat.
Compared to the diploid parents, polyploidy can make the:
–plant bigger and more robust
–flowers larger
–fruits bigger.
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An example is the strawberry plant. Diploid varieties of strawberry have smaller fruit
with less yields, whereas the tetraploid varieties have bigger and better yields.
Diploid vs. octoploid strawberries
Will you now be looking at strawberries with new and knowledgeable eyes?
Learning activity 9
How polyploidy improves crops
Design a poster, with key words to show the four ways that polyploidy improves
crops.
Mutagenesis
Mutagenesis is an important tool in crop improvement and is free of the regulatory

restrictions imposed on genetically modified organisms.
Mutation breeding (sometimes referred to as ‘variation breeding') is the process of

exposing seeds to mutagens (chemicals or radiation) in order to generate mutants
with desirable traits, e.g. larger seeds or sweeter fruits that are not found in nature.
Plants created using mutagenesis are sometimes called mutagenic plants or

mutagenic seeds. Currently there are over 1 000 mutant cultivars of major staple
crops being grown worldwide. Though poorly known, mutagenesis has produced
thousands of useful mutants and make up a sizable fraction of the world’s crops
including varieties of maize (711 lines), rice (534 lines), wheat (205 lines), barley,
pears, peas, cotton, peppermint, sunflowers, peanuts, grapefruit, sesame, bananas,
cassava and sorghum.
The use of mutagenesis to create novel variation is particularly valuable in those

crops with restricted genetic variability.
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Did you have any idea that so much of the food you eat has been cleverly
bred?
Use of seed banks to maintain biodiversity
All life on earth depends on plants. Plants are the basis of ecosystems in which all
animals, including humans, live, survive and grow. It is thought that 60 000 to
100 000 plant species are currently under threat. The root causes, human
population growth and socio-economic factors, are difficult to control but by saving
seeds, many of these plants could be saved.
What is a seed bank?
In modern terminology, a seed bank is a facility used to store seeds of various wild
plants and crops, in an effort to maintain biodiversity. There are also soil-stored seed
banks, e.g. those of the alien Acacia spp. Many countries have seed banks; two of
the most important facilities are in the United Kingdom and Sweden.
In the UK, Kew’s Millennium Seed Bank Project (MSBP) aimed to have conserved
10% of the world’s seed plants, mainly from dry lands (about 40 000 species) by
2010. It holds seeds from species thought to be extinct in the wild.
The MSBP works together with, amongst others, the South African National
Biodiversity Institute. South Africa’s aim is to contribute seed of about 2 500 of its
indigenous species to the MSBP, focusing on:
–endangered species
–endemic species
–species that might become endangered due to over-exploitation.
The Swedish International Seed Vault is found on the Svalbard Islands about 620
miles from the North Pole. This seed bank, in a reinforced concrete tunnel, drilled 70
metres into a mountain, aims to store 4.5 million seed samples from every country in
the world. The seeds, stored at –180C, will be viable for thousands of years.
How do seed banks help to maintain biodiversity?
Seed banks can be of great help to maintain biodiversity by offering protection

against loss of species in the wild.
Plant diversity has been negatively affected by many factors such as:
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habitat loss (e.g. because of agriculture, development of cities, building of dams,
large-scale ecological disasters, etc.)
climate change
over-exploitation of certain species.
To help maintain biodiversity, the high quality seed from the seed banks can be used
to produce plants for the:
re-establishment 0f damaged or destroyed habitats and ecosystems. For example,

the conservation of the seeds of dry-land species has become particularly important
as many plants species are under threat from desertification. Many of these plant
species are important to human survival as food, medicine, fuel wood and forage for
livestock.
re-introduction of newly extinct, endangered or threatened species back into the

environment.
production of plant material, as a source for research of over-exploited plants.

This is far better than over-exploiting wild populations, which could lead to them to
become endangered or extinct.
Note:
It is worthwhile noting that storing the seeds of both the wild and less productive
crop species is very important. It ensures that their genetic diversity is not lost
which could help safeguard future crop plants.
As food crops are currently selected for their high productivity, a new disease or new
environmental conditions, e.g. unusual drought, could negatively affect them. The
latter is particularly significant in the current times of climate change. The genetic
diversity of the stored crop species might supply useful genes. These genes could
be used to make the endangered crop plant more resistant or able to cope with new
environmental conditions.
Importance of seeds as a food source
Of the six major plant parts, seeds are the most important source of human
food. The other five major plant parts are roots, stems, leaves, flowers and fruits. A
great variety of species have edible seeds, mostly from flowering plants
(angiosperms). Seeds:
have great food value.
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are a very practical source of food as they are easy to transport and store well for
long periods.
Plants with edible seeds have been cultivated since ancient times and commonly
fall into three groups:
Grains (cereals), from grass-like plants, e.g. maize, wheat, rice, oats
Pulses (legumes, e.g. lentils, peanuts), from pea and bean plants
Nuts – any large, dry, oily seeds found within a hard shell and used as food
The food stored in these seeds can be used:
directly as food, e.g. rice, oats
for the manufacture of human food products, eg cooking oil from crushed sunflower
seeds and baking flour from milled wheat, rice etc.
maize
wheat
Why are grains and pulses so important?
Grains and pulses:
form the staple diet of most of the world’s population, e.g. maize,
wheat and rice. Every year these provide almost half of all the calories eaten in the
world.
have a high nutritional value; the principle nutrient is carbohydrate (starch) but they
also are a valuable source of protein, especially in poorer countries.
On their own, grains and pulses are not a source of complete protein but if eaten
together they are, eg samp (maize) and beans together form a complete protein: this
is the staple diet of many people in South Africa.
complete protein = protein that provides all the essential amino acids, e.g. meat,
dairy products, soybeans (the only plant protein to have this characteristic)
are cheap.
What is the value of each seed group?
Grains
Grains are important as they provide:
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a rich store of starch (60 to 80% of the seed from the endosperm is starch) which
provides a very good source of energy.
fibre, from the seed coat of whole grains, which helps keep the bowel healthy
preventing constipation and diverticulitis as well as protecting against colon cancer.
most of the B vitamins and many minerals from the seed coat (bran).
small amounts of protein and fats.
Pulses
Pulses such as lentils, peas, beans, peanuts and soya beans are important as they:
are a very good source of protein, minerals and vitamin Bs.
help regulate blood sugar levels. Pulses have a low glycemic index as their fibre
lowers the rate at which sugar is released from their starches during digestion, i.e.
they ‘burn slow’. This is very important in diabetic sufferers, and also for weight-loss
diets.
Nuts
Nuts, e.g. almonds, pecans, cashews:
are a very good source of energy, as they are, apart from animal fats, the most
calorie-rich natural food.
are rich in monounsaturated or polyunsaturated fatty acids.
supply one of the best natural sources of vitamin E.
Oil seeds
Several plants produce seeds that can be eaten as such or are processed to
produce vegetable oils, e.g. peanut, soybean, maize, sunflower and rape (canola)
seeds. These oil seeds:
are rich in monounsaturated or polyunsaturated fatty acids.
can contain vital omega-3 fatty acids, eg soya beans, flax seeds.
Learning activity 10
Importance of seeds as food
1.Match up the item in column B with that in column A. Record your answer, a letter,
next to the number from column A.
Column A Answers Column B
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1.grains (cereals) 1. ___ A.lowers the rate of sugar release
2. ___ during digestion
2.staple diet of most people in
3. ___
the world B.omega-3 oils
4. ___
3.rich store of starch 5. ___ C.nuts
6. ___
4.fibre of whole grains D.complete protein
7. ___
5.flax seeds 8. ___ E.grass-like plants
6.fibre of pulses F.prevents constipation and protects

against colon cancer
7.samp (maize) and beans in
combination G.grains
8.large, dry, oily seeds found H.grains and pulses

within a hard shell
(8)
2.Complete the following table showing the content of seeds.
Carbohydrates Oils Proteins Vitamins Roughage

high / low high / low high / low examples Useful - Yes/No
grains
pulses omit
nuts omit omit
(12)
Total [20]
The use of growth regulators in modern agricultural practices
In modern agriculture it is now accepted that the using of growth regulators is of

great benefit. Growth regulators can be either synthetic or natural (plant hormones)
and can either be growth promoters or inhibitors. They include auxins, gibberellins,
cytokinins, ethylene, abscisic acid and flowering hormones.
Plant growth regulators are for controlling and improving the natural plant growth
processes, which increases crop productivity. Productivity is improved as they:
bring about successful propagation, e.g. auxins and cytokinins (both plant
hormones), which control the growth and development of shoots and roots.
increase the size of fruit, e.g. gibberellins.
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induce early flowering and increasing the number of flowers, e.g. auxins. More
flowers will mean that more fruit is produced.
break the dormancy of some seeds.
increase the yield and oil contents of seeds and nuts.
control the ripening of some fruits, e.g. ethylene.
Short questions
1. Multiple choice
Various possible answers are given for the following questions. Fill in the correct
answer below.
1 2 3 4 5
1The advantage of sexual reproduction is that: (a) it is a fast process; (b) damaging
mutations may occur; (c) it causes genetic variation; (d) it prevents evolution.
2Which statement is true for all pollen grains? They: (a) are diploid; (b) are carried by
wind; (c) are carried by insects; (d) contain a male nucleus.
3Where does fertilisation take place in a flowering plant? (a) stigma; (b) bud; (c)
ovule; (d) anther?
4Which combination is true of asexual reproduction?

1. no variation
2. always involves meiosis
3. offspring genetically identical
4. two mates needed
5. mitosis usually involved
(a) 1, 2, 4; (b) 1, 3, 5; (c) 2, 4, 5; (d) 1, 4, 5.
5Tissue culture enables plant growers to produce plants: (a) more quickly than
normal; (b) only at certain times of the year; (c) that are not pathogen free; (d) slowly
and in small numbers.
[5]
2. Terms
Statement Term
1.Cell formed as a result of the fusion of two sex 1_______________________

cells
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2.Reproduction involving fertilisation of gametes 2_______________________
3.A group of identical organisms 3_______________________
4.An organism form by crossing two organism 4_______________________

with different genetic make-up
5_______________________
5.Condition mainly in plants where there is more
6_______________________
than two sets of homologous chromosomes
7_______________________
6.Fusion of male and female gametes
8_______________________
7.The process whereby a new gene with a
desirable trait is inserted into the DNA of a plant 9_______________________
8.Process of joining two parts of separate 10________________________

plants, a stock and scion
9.Transfer of pollen from anther to stigma
10.Structure the ovule develops into after

fertilisation
[10]
3. True and false
Decide if the statement is T (true) or F (false) and write T or F. If F, underline the

incorrect word/term. In the space, write the correct word/term.
Statement T/F Correct term
1.Sexual reproduction needs two specialised cells, 1.____________________

called ova.
2.____________________
2.Each sex cell contains only one set of
3.____________________
chromosomes in its nucleus.
4.____________________
3.Vegetative propagation ensures genetic diversity.
5.____________________
4.An advantage of sexual reproduction is that the
offspring are often stronger.
5.Vegetative propagation occurs more slowly than

propagation from seed.
[5]
4. Mix and match
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Choose a word or term from Column B to match the concept in Column A and write
down the correct letter next to the relevant number in the space provided.
1. tissue culture A. Carrying of pollen from stamens to stigmas
2. pollination B. Results in genetic variation
3. asexual C. Anther
reproduction
4. sexual D. No genetic variation

reproduction
5. produces pollen E. Mass production of plant material (callus) used in

bio-technology
[5]
Each of the questions consists of two items in the first column (1 and 2) and a
statement in the second column.
Write down your choice by using the following codes.
A if only item 1 relates to the statement
B if only item 2 relates to the statement
C if both items relate to the statement
D if neither item relates to the statement
Item Answer Statements
1. Gametes are involved 1. asexual reproduction

2. sexual reproduction
2. Fertilisation 1. production of pollen

2. production of zygote
3. Asexual reproduction 1. recombination of

genes
2. slower
4. Plant propagation using very tiny bits of 1. tissue culture
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plants 2. sexual reproduction
5. Advantage of sexual reproduction 1. can colonise new

areas
2. produces variation
[5]
2.3 Reproductive animal strategies

Reproduction is the production of a new generation of organisms from an existing
generation. Therefore it is a life process that ensures the continued survival of a
species.
What is the goal of each species?
The ultimate goal of each animal species is to produce the maximum number of
surviving offspring while using the least amount of energy. This is called
the reproductive effort.
Asexual reproduction, found in lower and microscopic animals, is energy efficient

(low reproductive effort) because it involves only a single animal. However, sexual
reproduction as happens in all vertebrates is much more complex, needing a much
higher energy input (high reproductive effort).
Unique reproductive strategies have therefore developed that will ensure

maximum reproductive success in different environments. This enables the species
to breed successfully and then survive to reproductive age.
strategy = genetically determined behaviour
The following reproductive strategies will be discussed:
A. Courtship
B. External versus internal fertilisation
C. Ovipary, ovovivipary and vivipary
D. Amniotic egg
E. Precocial and altricial development
F. Parental care
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A. Courtship
Courtship in animals is behaviour and/or signals that are designed to attract

another animal for mating and breeding.
What are the different forms of courtship?
Courtship strategies may be simple or complex.
1. Simple strategies
Simple strategies such as chemical (pheromones), visual (brightly coloured body

parts) or auditory stimuli are used for mates to find each other; they can be used
singly or in combination. For example:
Females of some insect species, e.g. moths produce species-specific

pheromones that guide males towards them.
Most frogs have to return to the water for mating and breeding. Once the males
reach the breeding ground they sing (grunt, croak) to attracts females. Each species
has its own song that only attracts females of that species.
Male birds advertise when they are ready to mate by singing a species-specific
song that attracts the female. Once they meet, the male must then impress and
stimulate the female sexually, often by special plumage, e.g. the metallic-green
breeding plumage of the male Malachite sunbird or extra-long tail feathers of
widowbirds.
2. Complex strategies
The more elaborate forms of courtship are unique to each species.
The females usually favour males that are:
larger
have more elaborate physical features
display more energy in courtship activity than other males.
This helps the female to choose the better male, which can reinforce pair bonding
(important for parental care) and promises healthier offspring (more will survive). For
example:
Certain bird species have complex courtship patterns, e.g. the Blue
Cranes’ courtship displays include:
- a complex and extended series of calls.
- elaborate dances by the males.
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Springbok have an annual rut (a period of sexual excitement), usually when the
animals are in peak condition. To attract females, males defend territories with loud
grunts, attack vegetation with their horns and deposit middens of urine and dung in a
ritualised display.
Most young are born six months later in the spring, shortly before the rainy season
begins.
The timing of this display ensures that:
-the mothers are in good condition, and
-the young are born when there will be enough food to enable them to reach
reproductive age.
This rutting strategy results in breeding only taking place if conditions are favourable.
Some birds species exhibit courtship-feeding, e.g. the male African hoopoes feed
insects to their mates. This allows the female to save her energy for incubating and
brooding.
Female hoopoe getting food from male
How will courtship maximise reproduction?
Courtship mechanisms ensure that males and females find suitable mates, e.g. the
strongest male.
Sexual behavior in courtship is timed so that the male and female are ready for
mating at the same time.
Energy expenditure is usually by the male, the female conserves her energy for
breeding.
As a result of these factors, it is more likely that strong healthy offspring will be
produced.
Human courtship, although it springs from the same drives and is directed at
the same goals, is so influenced by cultural circumstances that it is commonly
thought of in terms of custom rather than instinct.
B. External versus internal fertilisation
Fertilisation is the joining of the nucleus of an egg and a sperm. The sperm are
motile as they are able to swim but eggs do not move. Vertebrate species therefore
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have various ways of ensuring that sperm reach the eggs for fertilisation to take
place.
External fertilisation
External fertilisation takes place in water and occurs in most aquatic vertebrates,
e.g. fish and frogs.
It is not an ideal process as:
it is wasteful as huge numbers of eggs are produced. Most of the eggs (and many
young) are eaten.
fertilisation is not certain.
How can external fertilisation maximise reproduction?
As fertilisation is not certain in water, to maximise reproductive success, aquatic

animals must use various strategies. The following are some of the strategies.
Huge numbers of eggs and sperm are released into the water. A male frog sheds
millions of sperm and a female sheds 2 000 to 3 000 eggs in the water. This
increases the probability of fertilisation. With the large number of fertilised eggs there
are enough to grow into adults even though many are lost to predation.
Frog amongst frogspawn (eggs)
Courtship rituals, e.g. many fish swim side by side when releasing their eggs and
sperm which ensure that the male and female gametes are close to each other.
It is important to note that reproductive energy expenditure goes almost totally into
producing the large number of eggs.
Internal fertilisation
Internal fertilisation occurs in terrestrial vertebrates, e.g. reptiles, birds and

mammals. With no external water for the sperm to swim in, the male gametes are
released directly into the body of the female (during mating or copulation) and
fertilise the eggs inside the body.
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Courtship rituals
Most birds and reptiles mate using a cloaca – a single opening located in the
lower abdomen. During mating, the males and females line up their cloacae for the
transfer of sperm.
The males of virtually all mammals have a penis to introduce the sperm into the
female. This process is known as copulation.
The penis ensures that sperm is transferred successfully without being destroyed by
any environmental conditions. Once inside the female the sperm swim to the egg in
fluid – seminal fluid (from male) and mucous membrane fluids (from female).
How does internal fertilisation maximise reproduction?
Fertilisation is more certain as the gametes are placed as close together as

possible. Although this does not ensure fertilisation, it makes it much more likely.
Fewer gametes are therefore needed.
The internal fertilisation strategy means that the energy saved in producing fewer
gametes can be used for other purposes to maximise reproduction. For example a
protective shell and increased yolk can be produced or development can be internal
via a placenta.
Learning activity 1
Internal vs external fertilisation
Devise a concise mind map to show how each type of fertilisation improves the
chance of reproductive success.
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C. Ovipary, ovovivipary and vivipary
Ovipary, ovovivipary and vivipary are terms for reproductive strategies that describe
the moment at which the future offspring separates from a parent. These
strategies indicate:
where the embryos develop.
how the embryo and foetus are nourished.
Ovipary
In oviparous animals, eggs develop outside of the parent. This may be fertilised
externally or internally.
ovi- = egg; -parous = producing, bearing
The majority of animals are oviparous. Egg yolk is the only food that the
developing embryos receive until they hatch from the egg.
How does ovipary in aquatic environments maximise reproduction?
Most fish and amphibians are oviparous. The eggs are released into the water and
are fertilised externally. Enormous numbers of eggs, containing a small amount of
yolk, are needed as the eggs and developing embryos are very vulnerable to
predation. The vast numbers ensure the survival of the species but require a high-
energy input from the female. However, this is offset by less energy being needed for
yolk production and parental care.
There are interesting South African marine examples. The Catsharks are oviparous:
the females lay egg cases that are known as ‘mermaid’s purses’. These egg cases
contain the embryo and yolk supply, and the young shark eventually hatches out of
the case. Empty mermaid’s purses are often found washed up along the shore. The
egg case negates the need for large numbers of eggs as the developing animal is
well protected.
Catshark (above) and its egg case
How does ovipary in land environments maximise reproduction?

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The oviparous land vertebrates include birds and most reptiles (70%).
Very few eggs are produced, particularly by birds, thus saving energy that goes into:
–producing eggs with more food (nutrient-rich yolk and protein-rich albumen), which
allows the animal to be more fully formed at hatching.
–protecting and incubating the eggs before hatching.
–parental care for the young.
A shell protects the developing embryo from predators, pathogens, physical damage
and dehydration.
South African examples are birds and most reptiles, e.g. the python and green
mamba. Oviparous—or egg-laying—snakes tend to live in warmer climates, which
helps incubate their eggs.
Green mamba hatching
Python incubating its eggs
Learning activity 2
Ovipary
Devise a learning diagram to show how ovipary in land environments maximises

reproduction.
Ovovivipary
In ovoviviparous animals, the eggs that are fertilised internally are kept inside the
female body until they hatch. Therefore, offspring are born ‘live’.
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The embryo gets food from the large amount of yolk in the egg and is not dependent
on the mother except for physical protection and, often, gaseous exchange.
Ovoviviparity is surprisingly common and occurs in very many sharks.
A well-known example is the ragged tooth shark. Its eggs are fertilised internally. The
embryos initially feed on their own supplies of yolk. Later they feed on fertilised eggs
and on other developing embryos (known as intra-uterine cannibalism). As a result,
only two pups are born per litter.
The gestation period is 9 to 12 months, depending on the water temperature.
Ragged-tooth shark
How does ovovivipary maximise reproduction?
Ovovivipary occurs in some fish and reptiles, e.g. puff adder. Ovovivipary maximises
reproduction because:
fewer eggs are produced so mother’s energy expenditure is less.
the developing embryo is much less vulnerable to predation and cold temperatures.
the young are born fully developed so are able to get their own food and escape
predators more easily.
Vivipary
In viviparous animals, fertilisation is internal and the eggs do not have a shell.
The retained egg forms an embryo and then a foetus, which develops inside the
mother. It obtains continuous nourishment from the mother, usually through
a placenta, and is born live.
Vivipary occurs in:
placental mammals (eutherians)
about 55% of sharks and rays.
How does vivipary maximise reproduction?
In vivipary, the reduced number of eggs means that more energy is available to:
nourish and protect the embryo and foetus.
provide parental care after the young are born.
In this way, the chances of offspring surviving and reaching reproductive age are
greatly increased.
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A South African example of viviparity is the hammerhead shark. The female joins
with its developing young via the yolk sac that forms a connection with the mother’s
oviduct tissue. It is through this that the developing young receive nourishment until
they are ready for birth. The young are born alive and fully functional.
Hammerhead shark
D. Amniotic egg
Animals have been laying eggs for millions of years.
Early vertebrates, i.e. fish and amphibians, need to lay their eggs in water and
therefore cannot live far from water. These are simple eggs that have no shell.
Later vertebrates, the amniotes (reptiles and birds) can lay their eggs in terrestrial
environments as they no longer have to return to water for breeding.
Mammals are also amniotes but do not lay eggs: the eggs are retained in the body.
All amniotes produce eggs that, after fertilisation, develop extra-embryonic
membranes. These are fluid-filled membranes (amnion, allantois, yolk sac and
chorion) that allow the embryo to survive and develop on land – or in the case of
mammals, internally in the uterus.
Fertilisation is internal and the membranes develop after fertilisation.
Such an egg is called an amniotic egg.
The amniotic egg is a major evolutionary innovation. It allowed some of the first
reptiles to colonise dry land more than 300 million years ago and to radiate out into
many new terrestrial habitats.
Diagram of a typical amniote egg, e.g. a chicken’s egg
How does the amniotic egg maximise reproductive success?
The embryonic membranes of an amniotic egg maximise the development of the

embryo and foetus before hatching or birth. This will enable the offspring to survive
the harsh conditions on land more easily and successfully.
The fluid-filled amnion surrounds and protects the embryo against dehydration and
mechanical injury.
The allantois acts as a reservoir for nitrogenous waste in birds and reptiles. In
aquatic environments waste would pass directly into the water.
The yolk sac in birds and reptiles holds nutritious food for the embryos’
development.
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The chorion surrounds all the other membranes.
–In birds and reptiles it, together with the shell, allows gaseous exchange.
–In mammals it forms the placenta with the endometrium. The placenta, another
evolutionary novelty, serves many functions that allow the foetus to develop more
fully and safely. See next unit
E. Precocial and altricial development
Precocial and altricial are terms used to describe two basic strategies of
development that are related to the particular natural environment of each species.
These strategies, commonly seen in birds and mammals, have evolved to:
provide nourishment to the developing embryos and the young.
protect them from predation.
As a result, the offspring are more likely to survive to reproductive age.
There are two levels of development of new-born birds and

mammals: precocial and altricial.
Precocial development
Precocial species hatch or are born when they are almost fully developed. Parental
energy expenditure therefore goes into pre-natal developments. The females are
less involved after birth.
Precocial species at birth or hatching:
have open eyes and hair or down.
have large brains relative to their body size.
are immediately active and mobile, even though they may not be very steady on their
feet.
are usually not confined to nests, i.e. birds, and have well-developed legs and feet.
Precocial young are born nearly fully developed
How does precocial development maximise reproduction?
The precocial features help offspring to:
find and eat food on their own, i.e. feed themselves.
look after themselves against predators by fleeing or defending themselves by

camouflage, e.g. an ostrich chick.
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Camouflaged ostrich chick
As a result, the offspring with these characteristics have a good chance of surviving
and reaching reproductive age.
What are examples of precocial species?
Most ground-nesting bird species, e.g. penguins, domestic chickens, ducks and
ostriches.
Jackass penguin on its nest
Many large mammals, e.g. elephants, many grazing animals (ungulates, e.g.
wildebeeste) and hares.
The precocial characteristics allow the young to run and hide from predators and to
keep up with a herd as it moves.
Altricial development
Altricial species are born or hatch when they are not well developed. Parental
energy expenditure thus goes into post-natal development of the offspring.
Altricial species at birth or hatching:
are often naked, lacking hair or down.
cannot walk or fly (the legs and wings are poorly developed).
Naked and blind newly hatched bird
often have closed eyes.
rely entirely on their parents for warmth (cannot thermo-regulate), transport and food.
Altricial young birds
have a coloured mouth-lining or gape-edge (birds).
require care and protection for a comparatively long time.
How does altricial development maximise reproduction?
This strategy will allow more offspring to reach reproductive maturity because:
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there is parental care; parents having used less energy in the pre-natal stage have
more energy for feeding, brooding (keeping young warm) and protecting the young
after hatching or birth.
the offspring reach reproductive age quickly because they:
–are easier to feed as they stay in the nests.
–grow very rapidly as they are fed large nutrient-rich food items, e.g. insects,
regurgitated meat.
they are safer from predation as the nests are inaccessible and the offspring only
leave the nest after they are full grown and ready to evade predators.
What are examples of altricial species?
Normally, altricial offspring are a feature of:
small mammals that produce big litters, e.g. rodents, cats and dogs.
humans, although they do not produce large litters. The reason for humans being
altricial will become clear when you study the next unit on Human Reproduction.
tree-nesting birds (or those that have nests away from the danger of predation).
marsupials, where the young are cared for in a pouch.
Learning activity 3
Precocial and altricial
By doing simple diagrams complete the table below.
Precocial Altricial
Features
Why the strategy maximises reproductive success
F. Parental care
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Parental care is any pattern of behaviour in which a parent spends time or
energy to improve the survival, condition and future reproductive success of
the offspring.
Such care needs high-energy input (high reproductive effort) from the parents before
and after birth. The diagram below shows that with parental care, fewer eggs need to
be produced, d.i. energy goes into care rather than into egg production
To show the result of parental care on number of eggs produced versus

offspring that survive to reproductive age
Parental care is found in a wide range of animals including both exothermic (fish,
amphibians and reptiles) and endothermic (birds and mammals) animals.
Care can be given at any stage, for example:
pre-natal care – guarding eggs, building nests, carrying broods, incubating eggs
and placental nourishing (mammals).
post-natal care – providing food, protecting offspring, teaching offspring.
In animals that provide parental care, females are generally the ones that carry it out.
Parental care by both sexes (biparental care) is much less common and exclusive
care by the male is rare.
Fish
Most fish species show no parental care and no fish feed their young. However, in
about 20% of fish families there is a little parental care.
Care typically involves building nests, guarding eggs and hatchlings from predators,
fanning eggs to increase oxygen supply, cleaning eggs to eliminate fungus and
having a brood pouch, e.g. sea horses.
Male sea horse with its brood pouch of embryos
Amphibians
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Most amphibians have to return to the water for reproduction. Much of their parental
care is directed to minimise the loss from predators of eggs and embryos by:
egg guarding, e.g. eggs of the midwife toad are kept and carried on the rear end of
the male.
A mass of amphibian eggs, appearing

as small black spots, is contained
within a gelatinous mass while they
incubate in a freshwater pond. Eggs
deposited in this fashion receive little
or no parental protection and will
soon hatch into small, wriggling
tadpoles.
Midwife toad
building terrestrial-breeding sites away from the water, for example the Foam
Nest frog female secretes a fluid that is churned up with her hind legs into a foam
ball to form a nest in trees that hangs over water. The fertilised eggs are protected
and stay moist inside the ball. Once the tadpoles hatch, they drop into the water.
Nest of Foam Nest frog
Reptiles
Reptiles show virtually no parental care besides guarding eggs (few lizards and
snakes), incubation by body heat (pythons) and attacking predators of their young
(pythons).
Birds
Birds show extensive parental care; most commonly by both parents.
Examples of parental care
Incubation of eggs by using body heat to keep eggs at an optimum temperature for
embryo development.
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Nest building is a vital part of parental care. Nests keep eggs in one place for
incubation and are usually positioned to protect the eggs against predators and
environmental factors such as sun and rain.
Brooding (as the offspring cannot thermo-regulate) and feeding of altricial species for
several weeks.
Protecting against predators.
Teaching young how to get food.
Mammals
Most young mammals are completely helpless at birth, requiring intense parental
care to grow up and mature into a state of reproductive readiness.
What are characteristics of parental care?
Mammalian parents have an innate drive for caring for the newborn. This greatly
increases the chance of survival and well-being of the young until they reach
reproductive age.
Maternal care, the predominant form of parental care, includes the following:
–Lactation, to feed the newborn. The composition of each species’ milk is perfect for
the best possible development of that species.
–Protection against predators and the cold.
Rodent mother with her helpless young
–Teaching how to gather food
–Licking newborn immediately after birth by most mothers establishes a unique

relationship. If no licking occurs, the newborn rejects the mother.
Cat licking its newborn
Paternal care occurs in a few mammalian orders and usually involves feeding the
young (e.g. carnivores) and guarding against predators.
Special nests (burrows) are made by many mammals, particularly rodents and
carnivores for warmth and protection, e.g. African wild dogs and naked mole-rats.
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Young African wild dog pups coming from their burrow
Learning activity 4
Reproduction strategies
1.What form of fertilisation takes place in fish and frogs? (1)
2.What form of fertilisation takes place in birds, reptiles and mammals? Why must it
be different to that in fish and frogs? (1 + 4)
3.What reproductive strategy do most fish, frogs, reptiles and all birds share? (1)
4.In which strategy, oviparity, ovoviviparity or viviparity, is fertilisation internal and the
egg has no shell?
Which of the following shows this strategy?
All mammals; placental mammals (1 + 1)
5.Which two groups of animals most often show precocial and altricial developmental
strategies? (2)
6.What is the specific name given to the eggs of reptiles, birds and placental
mammals? Why do this form of egg allow animals to leave the water and breed on
land? (1 + 3)
7.Fill in the labels of a hen’s egg shown below. (5)
8.Mention two ways that frogs protect their eggs from predation. Give examples. (4)
9.Does the mother, father or both bird parents commonly care for the eggs and
young? (1)
10.List the four main aspects of the parental care shown by birds. Differentiate
between altricial and precocial species where necessary. (6)
11.In which group of animals is parental care the most advanced? Which parent
does most of the caring? (2)
12.What is probably the most significant aspect of parental caring in the above
group? (1)
13.What reproductive developmental strategy does each photograph below show? In

each case, give one reason for your answer.
How does each strategy maximise reproductive success? (3 + 3)
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Total [40]
How effective for survival are the reproductive strategies of K-strategy and r-
strategy species?
Example of K-strategy species
Elephants are examples of K-strategy animals. Like the turtles they are long lived,
average life expectancy of 70 years. Although sexually mature in their early teens,
elephants generally only start to mate at about 20 years.
Typical of the K-strategy only a few offspring are produced. Female elephants have
babies about three years apart, and they have only one each time.
As they have a high level of parental care the young have a good chance of survival.
The whole group looks after the youngsters, and protects them through childhood
and adolescence. In this way most babies born will reach adult hood.
These tend to be a climax species as they produce only slightly more offspring than
the maximum that the environment can hold, i.e. the population density
(numbers/size) is often close to the carrying capacity (k). However, in the Kruger
National Park, probably due to fencing that prevent migration, the elephant
population in is well over the carrying capacity. Much destruction by surplus
elephants is evident in the KNP.
Example of r-strategy species
Leatherback and loggerhead turtles are examples of r-strategy species. The turtles
are long-lived, estimated to be between 50 and 100 years. They are only sexually
mature at a late age, about 17 years. years. This allows the female turtle to use her
energy to produce large numbers of eggs when she does not need the energy any
more for growth.
Leatherback turtle on beach
Typical of r-strategists female turtles lay numerous eggs (in multiple clutches of 90
and 130 eggs each) every two to three years. The eggs are laid in an egg cavity on
northern beaches along the east coast of South Africa.
Clutch of turtle eggs
As turtles give no parental care only a few of the eggs and offspring will survive.
Between two and ten per 1000 of laid eggs will reach adult hood.
Low survivorship is due to predation of eggs, by birds and ants, and hatchlings by
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ghost crabs and birds.
Predation of hatchlings continues in the sea, by large fish and octopus, until they
reach the currents that move them away from the coast.
Predation pressure decreases with increasing body size. The older turtles are
predated by large sharks.
Nevertheless the species survives as the r-strategy of the sea turtles allows them to
cope with high levels of egg and hatchling predation. But one does wonder at the
effect of predation by man.
Humans and sea turtles have similar life spans, but sea turtles have many more
offspring than humans. Which do you think has a better chance of surviving, a
recently hatched sea turtle or a baby human? Discuss in class.
What are survivorship curves?
Each species has a particular pattern of mortality. This is usually expressed as a

survivorship curve.
Study the graph below which shows the numbers of survivors out of 1 000 during the
life cycle of three different species: A – elephants, B – bird, C - turtle
Explanation
Convex curve – A shows that -
most of the offspring become adult;
mortality (death) occurs mainly among older individuals.
Reason: These species have a high level of parental care and, therefore, a high
survival rate.
Examples: This curve is found in K-strategy species, e.g. elephants, man.
Straight line – B shows that -
mortality decreases steadily with time and,
a young organism is just as likely to die as an old one.
Examples: many birds and plants
Concave curve – C shows that -
few offspring become adult,
they have a high mortality rate when young, and
when they are established there is an improvement in life expectancy.

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Reason: These species have no parental care and, therefore, have a low survival
rate when young.
Examples: This curve is found in r-strategy species, e.g. turtle, which produce large
numbers of eggs but only a few eventually mature and become adults.
Learning activity 5
Short questions
1. Mix and match
Match each description in Column A with an item in Column B. Write the letter under
the relevant number.
Column A Column B
1.ovoviviparity A.Ovipary, ovovivipary and vivipary; amniotic egg
2.female mammals B.Father looks after offspring
3.aquatic vertebrates C.Copulation necessary
4.reproductive D.Eggs are produced and released by the female

strategies
5.oviparous E.Lactate to feed newborn
6.precocial species F.Feed themselves
7.viviparous G.Allowed the first reptiles to colonise dry land
8.paternal care H.Fertilised egg with much yolk retained in female
9.internal fertilisation I.Fertilisation is internal and the eggs do not have a

shell
10.amniotic egg J.Mass release of eggs
1 2 3 4 5 6 7 8 9 10
[10]
In each case, write down if the statement is true or false, and if false, write down the
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word word
1.All oviparous animals have internal fertilisation.
2.All fish, reptiles and mammals have internal

fertilisation.
3.Nesting birds that hatch at a late stage of

development are altricial.
4.Internal fertilisation relies on chance; only a small

proportion of young will survive to reproduce.
5.Oviparous refers to animals that lay eggs that hatch

after leaving the body of the female.
6.Less energy is spent on egg production than on

parental care in marine animals.
7.In oviparity and ovoviviparity the fertilised egg is

kept within the mother’s body where it grows until the
young animal is born.
8.Parental care is behaviour that should result in

improving the reproductive success of the offspring.
9.External fertilisation is wasteful and uncertain.
10.Energy is wasted on egg production for internal

fertilisation.
[10]
Total [20]
Most young mammals require intense parental care
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2.4 Human reproduction
Human beings are unisexual with two separate sexes – male and female.
Male reproductive system
Male reproductive organs
What makes up the reproductive organs?
Primary sex organs – the testis
Ducts – epididymis, sperm duct (vas deferens) and urethra
Accessory glands – e.g. prostate gland
External genitalia – the penis
Scrotum
The scrotum contains the testis.
Functions
The scrotum acts as a temperature regulator, keeping the testis 2 to 3°C lower
than body temperature. The lower temperature is necessary for the formation of
fertile sperm.
In cold conditions testis are pulled closer to the abdomen for warmth. In warm
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weather the testis are suspended well away from the body. In this way the
developing sperm are always kept at a constant temperature.
The scrotum houses and protects the testis.
Testis
The testis, two oval structures, are suspended outside the body in the scrotum.
In the embryonic stage the testis are in the abdominal cavity just below the kidneys.
Before birth they descend into the scrotum.
The testis consist of many compartments or lobules, which contain highly convoluted
tubules, the seminiferous tubules. These total about 250 metres in each testis.
Germinal epithelium lines the tubules.
Between the tubules are groups of endocrine cells, the interstitial cells, or cells of
Leydig.
Functions
The testis produce:
sperm (male gametes), by the germinal layer
testosterone (a male hormone), by the interstitial cells.
Learning activity 1
Testis structure
After reading the preceding text, supply labels for numbers 1 to 5.
Total [5]
Ducts
The ducts include the:
a. Epididymis
b. Sperm duct
c. Urethra
a. Epididymis
The seminiferous tubules join to form the epididymis, a highly convoluted tubule
about 5 metres long.
Functions
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Immature sperm enter the epididymis where they:
1.mature, to become motile and fertile.
2.are stored for several months.

If they stay there any longer they are broken down by the epithelial cells of the
epididymis and re-absorbed into the body.
b. Sperm duct (vas deferens)
The muscular sperm duct is a continuation of the epididymis. It leaves the scrotum,
passes through the prostate gland and then enters the urethra.
Function
The sperm duct pushes mature sperm forward by strong peristaltic waves, from
the epididymis into the urethra. This is known as ejaculation.
peristaltic wave = strong contraction of smooth muscle in the walls of ducts
c. Urethra
The urethra is the duct at the end of the uro-genital system leading to the exterior.
Function
The urethra forms a common duct for the transportation of semen and urine,
although these two processes never occur together.
Prostate gland
The prostate gland, a plum-sized gland, surrounds the urethra at the base of the
bladder.
With increasing age this gland may enlarge and exert pressure on the urethra, which
slows down the emptying of the bladder. The prostate gland can be removed
surgically.
Function
The prostate gland secretes a fluid that aids the transport of the sperm and
contains enzymes that make sperm more active. This fluid makes up about 1/3 of the
seminal fluid (semen).
Cowper’s gland
The two Cowper’s glands are found at the base of the penis.
Function
Cowper’s glands produce an alkaline mucous-like fluid when sexually aroused. This
fluid:
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1.neutralizes acidic urine that may still be present in the urethra.
2.lubricates the urethra and external urethral opening to protect sperm from
mechanical damage during ejaculation.
Penis
The urethra passes down the male external organ, the penis.
The penis consists of special spongy tissue (erectile tissue). Running the length of
the penis there are three sections of erectile tissue. Two are situated on the dorsal
side, the corpus cavernosa, and one on the ventral side, the corpus spongiosum.
Diagram of cross section through penis
The primary mechanism that brings about an erection is the dilation of dorsal and
central arteries supplying blood to the penis. This allows more blood to fill the three
spongy erectile tissue chambers, causing the penis to lengthen and stiffen. This is
called an erection. Without an erection sperm cannot be transferred to the female’s
vagina during sexual intercourse.
The head of the penis is very sensitive and is protected by the foreskin. The foreskin
is sometimes removed in a simple operation known as circumcision, which may be
done for religious and cultural reasons or because the foreskin is too tight.
Function
The penis deposits semen with sperm into the female’s vagina during copulation. In
this way sperm are brought closer to the egg for fertilisation, which increases the
chance of fertilisation.
What is distinctive about the human penis?
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The human male is the only mammal that has no erectile bone (baculum) in the
penis; it relies entirely on engorgement (filling up) with blood to reach its erect state.
The human penis is not attached to the abdominal wall but hangs free. This is in
contrast to most other mammals where the penis is stored internally until erect.
Semen (seminal fluid)
Semen consists of:
sperm from the testis
seminal fluid from the sperm duct and accessory glands, e.g. prostate.
The average volume of semen for an ejaculation is 2.5 to 5 ml, and the average
number of sperm ejaculated is 50 to 150 million per ml, i.e. 700 million per
ejaculation. Semen with a sperm count of less than 20 million per ml is regarded as
being infertile.
What is the difference between an erection and ejaculation?
An erection is the stiffening of the penis.
Ejaculation is the expulsion of semen.
Learning activity 2
Male reproductive organs
1.What is the significance of the testis being positioned outside the body? (2)
2.Name the hormone produced by the testis. (1)
3.In what structure are the seminiferous tubules found? (1)
4.Which gland often enlarges in elderly men? (1)
5.What is the function of this gland? (2)
6.The picture below is a cross section through the penis.
Supply labels for:
a. ________________________________
b. ________________________________
c. ________________________________
d. ________________________________
e. ________________________________
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(5)
7.Explain how an erection of the penis occurs. (2)
8.What structure causes the semen (and sperm) to move? (1)
9.What makes up semen? (2)
10.Where are sperm stored? (1)
11.Why is the human penis unique in the animal kingdom? (2)
12.List, in order, all the structures a sperm travels through from where it is made until
its release from the body. Also, mention the gland it passes through. (5)
Total [25]
Female reproductive tract
The reproductive role of the female is far more complex than that of the male. Not
only does she produce eggs (ova) and the female hormones (oestrogen and
progesterone), but her body must also prepare to sustain (look after) a developing
foetus for about nine months, i.e. 280 days.
Female reproductive organs
The female reproductive organs include the:
ovaries
accessory organs – fallopian tubes (oviduct), uterus and vagina
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external genitalia (vulva).
Note:
As can be seen in the right hand diagram the urethra (urinary system) and vagina
(reproductive system) open separately. In males, the urethra carries both semen and
urine.
Ovaries
The ovaries are two almond shaped organs found in the pelvic cavity and held in
position by ligaments.
A germinal epithelium layer surrounds each ovary.
Primary follicles, tiny sac-like structures containing an immature egg, are embedded
in the outer layer. A girl child is born with these primary follicles so the total number
of eggs is determined at birth, i.e. 200 000 – 400 000. Compare this to the testis,
where millions of sperm are formed each day.
A primary follicle develops into a mature follicle (Graafian follicle).
Section through ovary showing primary follicles and mature follicle (Graafian
follicle)
After ovulation (release of an egg), the Graafian follicle forms the corpus luteum
(yellow body).
Functions
The ovaries:
1.form and release eggs.
2.produce oestrogen and progesterone.
Fallopian tubes (or oviducts)
The two fallopian tubes are muscular tubes lined with cilia. They stretch from each
ovary to the uterus. Each ends in a funnel shaped structure, the infundibulum that
has finger-like outgrowths, the fimbria.
Unlike the male duct system, which is continuous with the tubules in the testis, the
fallopian tubes have no direct contact with the ovaries.
Functions
The fallopian tubes:
1.provide a pathway between uterus and ovary for eggs, sperm and the zygote.
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2.are the site of fertilisation and initial cell division of the zygote.
3.enable the egg or developing zygote to move towards uterus (by the action of
muscles and cilia).
Learning activity 3
Fallopian tubes
Devise a diagram to show the structure and functions of the fallopian tubes.
Uterus
The uterus (womb), a hollow, pear-shaped thick-walled, muscular organ, is situated

between the bladder and the rectum. During pregnancy it enlarges considerably but
soon after birth almost returns to its original size.
The lower part, the cervix, projects into the vagina. Normally its opening is only
millimetres in diameter allowing menstrual blood to leave the body and sperm to gain
access. It must therefore dilate enormously during the birth process. The sphincter
muscles of the cervix keep the uterus closed during pregnancy preventing a
miscarriage.
The uterine wall consists of the:
–myometrium, a thick involuntary muscle layer. Walls need to be thick so that it can
stretch when a baby develops inside it.
–endometrium, a lining that is richly supplied with blood vessels.
Section of uterine wall
➢At ovulation progesterone causes the endometrium to thicken to prepare for the
implantation of the blastocyst.
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➢If fertilisation does not occur the upper layer of the endometrium becomes
detached and is passed out together with the unfertilised egg. This occurs roughly
every 28 days and is known as menstruation.
Functions
1.The uterus is the organ in which the blastocyst implants, develops and grows.
2.The contraction of the myometrium enables the baby to be pushed out during birth.
What is distinctive about the human uterus?
Human females are higher primates and therefore have a simplex uterus in which
there is no separation between the horns and is thus a single cavity.
Early placentals (rodents and rabbits) have a duplex uterus with two completely
separated uterine horns and separate cervices opening into the vagina. Over time
the two horns started fusing until a uterus with a single cavity was formed.
Vagina
The vagina or birth canal is a muscular passage between the uterus and the outside
of the body.
It has very elastic, folded walls, which allows it to stretch during intercourse and
childbirth.
The pH of the vagina is normally quite acidic which helps keep the vagina healthy
and free from infection.
Functions
The vagina:
1.is the place where sperm are deposited during sexual intercourse.
2.forms a birth canal during birth.
Vulva
The vulva forms the external genitalia and plays no role in the reproductive process.
Clitoris
This is a small mass of erectile tissue, found at the anterior end of the vulva. It is the
female counterpart of the male penis and plays a role in sexual excitement of the
female.
Learning activity 4
Structure and functioning of the female reproductive system
Study the diagram below of the female reproductive system.

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1.Write down the number and name of the part(s) which:
1.1forms the eggs (2)
1.2is a funnel-shaped structure into which released egg are swept (2)
1.3is the area where fertilisation takes place (2)
1.4is made of involuntary muscles and contracts during childbirth (2)
1.5is shed during menstruation (2)
1.6secretes the hormones, oestrogen and progesterone (2)
1.7part of the uterus projecting into the vagina (2)
1.8is a cavity in which the foetus develops (2)
2.Give the two main functions of ovaries. (3)
3.Why is the uterus of a human (a higher primate) unique among mammals? (1)
Total [20]
Puberty
The process of physical and physiological changes is called puberty. It leads to:
the development of secondary sex characteristics.
an immature individual (child) becoming capable of reproduction.
The age at which puberty begins is mainly affected by genetic factors. In girls,
puberty occurs between the ages of 11 and 14, and in boys between the ages of 14
and 16.
164
However, in warmer climates, puberty can start earlier while in cooler climates, one
or two years later.
This period of physical, physiological as well as psychological change is known

as adolescence. It extends from the start of puberty for a number of years, e.g. until
the age of 17 to 20 (females) and 18 to 21 years (males). With all these changes
going on, it is not surprising that behaviour at times may be affected.
How does puberty start?
The pituitary gland, under stimulation from the hypothalamus,

releases gonadotropins (hormones that stimulate the gonads), which initiate
puberty.
–In males, interstitial-cell-stimulating hormone (ICSH) stimulates the testis to

secrete testosterone.
–In females, follicle-stimulating hormone (FSH) stimulates the ovaries to produce

oestrogen.
Testosterone and oestrogen then initiate changes to the gonads and to other parts
of the body.
The results of changes to the gonads are called primary sexual characteristics as
they influence the process of reproduction. Other physical changes are referred to as
165
secondary sexual characteristics as they have nothing to do with the actual
reproductive process.
What physical changes occur during puberty in girls?
The physical changes of puberty include the following:
breast development; normally the first sign of puberty starts between 10 and 12
years old.
growth of hair in the pubic area and armpits, at about 11-12 years, is often the
second noticeable change.
increase in size of uterus, ovaries and the primary follicles.
widening of pelvis and thus the hips, to provide a wider birth canal.
deposition of fat on hips, thighs, upper arms and buttocks.
start of the 28-day menstrual cycle. The average age of starting is between 12 and
18 years.
the first menstrual bleeding, referred to as menarche. It typically occurs about two
years after breast development starts.
menstruation is unique to humans and close primate relatives such as chimpanzees.
ovulation, which in about 80% of girls only occurs after the first year of menstruating.
growth spurt lasting two to three years occurs.
possible acne as the skin gets oilier.
What physical changes occur during puberty in boys?
The physical changes of puberty include the following:
enlargement of testis and penis, usually the first sign of puberty. Maximum size is
reached about 6 years after the onset of puberty.
hair growth in the pubic area and armpits, at about 13 to 14 years; facial hair grows
later.
increase in size of larynx (voice box) and thickening of the vocal cords, which causes
the voice to deepen.
enlargement of skeletal muscles and broadening of shoulders. By the end of puberty

the bones are heavier and muscle mass is nearly double.
sperm production begins.
growth spurt of two to three years occurs. Ever wondered why teenage boys eat so
much?
166
acne can occur; it is more common in boys than girls. It cannot be prevented or
easily reduced, but usually disappears at the end of puberty.
Learning activity 5
Physical changes during puberty
In cartoon form, draw two figures, male and female, showing the changes that occur
during puberty.
Distinctive human sexual activities
Human males are sexually fertile all the time; males of most mammalian species are
not.
Menstruation is unique to humans and close primate relatives such as chimpanzees.

The females of other placental mammal species have oestrous cycles, in which the
animal reabsorbs the endometrium if fertilisation does not occur during that cycle.
oestrous = a time when females ovulate and can be impregnated
Mating in humans and to a lesser degree in most other higher primates is not
confined to the period when ovulation occurs. This mating is designed to reinforce
pair-bonding; especially necessary where care of the young is prolonged as in
humans.
Nocturnal emissions (‘wet dreams’) occur in celibate males. celibate = abstaining
from sex
Life cycle of humans
The diagram below shows a simplified life cycle to show the major reproductive
processes.
Gametogenesis
Gametogenesis is the formation of mature gametes (sperm and eggs) by the

reproductive glands (gonads).
167
It involves meiosis, a unique kind of nuclear division, which results in a halving of the
number of chromosomes: from 46 (in body cells) to 23 (in gametes). This is to
ensure that on fertilisation, the number of chromosomes returns to 46 in the fertilised
egg (zygote).
Spermatogenesis
Spermatogenesis is the sequence of events during which mature, haploid sperm

are produced from the germinal epithelium in the seminiferous tubules of the testis.
The hormone, testosterone, is essential for the making of sperm.
Spermatogenesis begins at puberty, between the age of 14 and 15, and continues
throughout life.
Every day a healthy adult male makes about 400 million sperm. The large number
increases the chance of fertilisation.
Phases of spermatogenesis
There are four phases in the process – the multiplying phase, growth phase,
reduction phase and differentiation phase.
Multiplying phase
The diploid (2n) spermatogonia (germ cells) of the germinal epithelium divide
repeatedly by mitosis to form new spermatogonia (2n).
Growth phase
Some spermatogonia mature and grow in size to develop

into primary spermatocytes (2n).
Reduction phase
The primary spermatocytes undergo the first meiotic division, which is a reduction
division, each forming two haploid secondary spermatocytes (n) with 23
chromosomes.
These undergo the second meiotic division, resulting in four haploid spermatids –
small round cells.
Differentiation phase
During this phase the spermatids lose cytoplasm and unnecessary cell organelles
and differentiate into immature sperm.
The diagram below shows the four phases.
168
Spermatogenesis takes about 72 days from primary spermatocyte to immature
sperm.
The immature sperm are moved into the epididymis where they mature, becoming
motile and fertile, and can be stored for several months.
To summarise
Diploid cells in the seminiferous tubules of the testis undergo meiosis to

form haploid sperm cells.
Learning activity 6
Summary of spermatogenesis
Complete the following sentences:
1.Spermatogenesis takes place in the ______________________ of the testis.
2.The germinal layer produces extra spermatogonia by the process of

____________.
3.These diploid cells undergo _______________ to each produce four

(haploid/diploid) _________________.
4.The spermatids undergo _______________ to form sperm.
Total [6]
Structure of a sperm
A sperm is the smallest of all human cells and consists of a head, neck, body and
tail.
Once ejaculated, the sperm can survive in the female reproductive tract for about 48
hours. This is possible as it obtains nourishment from seminal fluid and female
secretions.
Learning activity 7
169
Spermatogenesis
Question 1
The micrograph below is a cross section of a part of the male reproductive system.
1.Identify the part. (1) _________________
2.Supply the missing labels.
(3)
3.What process takes place in these structures? (1)
[5]
Question 2
The diagram below represents part of a section of a testis, greatly magnified.
1.Which part of the testis does the diagram represent? (1)
______________________
2.Give the name and the number of the cells where:
2.1the hormone testosterone is produced (2)

170
2.2cells are undergoing mitosis (2)
2.3the first meiotic division is taking place (2)
2.4cells are undergoing second meiotic division (2)
2.5differentiation is taking place (2)
2.6there are very many mitochondria. (2)
3.The very large cell (7) in the drawing, the cell of Sertoli, contains a large amount of
dissolved nutrients. What do you think its function is? (2)
[15]
Question 3
The diagram below shows a human gamete.
1.Name the gamete. (1)
2.Give labels for the parts A to D. (4)
A _______________
B _______________
C _______________
D _______________
3.Give the name and number of the part that contains:
3.1the chromosomes (2) ______________
3.2contractile fibres. (2) ______________
4.Name the parts numbered 1, 4 and 5 and mention one function of each of these
parts. (3 x 2)
[15]
Total [35]
Oogenesis
The production of haploid, mature eggs in the follicles of the ovaries is known as
oogenesis.
Oogenesis follows mainly the same sequence as spermatogenesis. There are some
differences which include:
171
The number of eggs is determined before birth. Oogonia were produced by mitosis
and growth from the germ cells of the germinal epithelium before birth.
The mature eggs, unlike sperm, are not formed continuously throughout life. This
process starts at puberty and stops at menopause.
Oogenesis occurs in a monthly cycle, or menstrual cycle, where an egg reaches

maturity approximately every 28 days while sperm are produced daily.
Phases of oogenesis
Multiplying phase
Before birth, germ cells from the germinal epithelium which surrounds the ovary, sink
in and divide by mitosis to form the primary follicles.
Each follicle has a large central cell, the oogonium (2n) surrounded by a single layer
of cells, the theca.
Growth phase
From puberty onwards, the primary follicles start periodically growing and developing
to form Graafian follicles.
Within each Graafian follicle the oogonium grows into a primary oocyte (2n).
Reduction and maturity phase
The primary oocyte (2n) undergoes meiosis resulting in an egg (n).
There is no splitting of the cell during this meiosis. Of the four haploid nuclei one will
form the nucleus of the egg. The other three will degenerate. See the diagram.
Mature Graafian follicles move periodically to the surface of the ovary, where they
burst, releasing the mature egg and surrounding follicle cells. A process called
ovulation.
What is ovulation?
Ovulation is the release of a mature egg from a Graafian follicle in the ovary every
28 days. The egg survives for 24 hours after ovulation.
To summarise
Diploid cells in the ovary undergo meiosis to form a primary follicle consisting
of haploid cells. One cell develops into an ovum contained in a Graafian follicle.
Structure of an egg
The diagram below shows the structure of an egg with functions of its parts.
172
Menstrual cycle
In human women the length of a menstrual cycle varies greatly (ranging from 21 to
35 days), with 28 days as the average length. It includes the uterine and ovarian
cycles. These cycles occur from puberty until menopause.
Both cycles are controlled by the endocrine system.
1. The ovarian cycle
The ovarian cycle consists of the the:
Development of Graafian follicle
Ovulation
Formation of the corpus luteum
Development of the Graafian follicle (follicular phase)
The follicular phase is the first part of the ovarian cycle. During this phase, the
primary follicles mature and get ready to release an egg.
Through the influence of follicle stimulating hormone (FSH), from the pituitary gland,
during the first days of the cycle, a primary follicle is stimulated. The follicle, one of
many present at birth, develops into a Graafian follicle.
Ovulation
The Graafian follicle contains the ovum (egg cell). As the follicle matures and
enlarges it moves to the surface of the ovary. Approximately mid-cycle, a second
hormone luteinising hormone (LH), also released from the pituitary gland causes the
causes the Graafian follicle to rupture releasing an ovum in an event called
ovulation. This takes place approximately on day 14 of the cycle.
Formation of the corpus luteum
After ovulation the remains of the Graafian follicle, under the influence of FSH and
LH changes into glandular tissue called the corpus luteum (yellow body). This
structure produces large amounts of progesterone as well as oestrogen.
If pregnancy does not occur, the corpus luteum will begin to disintegrate and
disappear 10 to 14 day after ovulation. If pregnancy does occur, it remains as it is
needed to sustain a healthy pregnancy.
What makes human ovulation unique?
173
Human females can be sexually active at any time in their cycle, even when they are
not about to ovulate.
Other mammal females are only sexually active in the oestrus phase of their cycle,
i.e. when ‘in heat’ and are about to ovulate.
There are no obvious external signs or sexual excitement to signal ovulation. It is

pure chance as to whether fertilisation occurs, unlike in other animals.
Changes in the ovary during ovarian cycle
2. Uterine cycle
The uterine cycle is a series of changes in the endometrium and is regulated by

hormones.
It may be divided into two main phases:
Changes in the endometrium
The hormone oestrogen, secreted from the maturing follicles starts the repair of the
endometrium. Days 6 – 14 of the menstrual cycle.
Later under the influence of the two hormones (oestrogen and progesterone) from
the corpus luteum the endometrium continues to thicken, becoming more glandular
(secretes mucus and nutrients) and vascular (has blood vessels). It is now suitable
for the implantation of a fertilised egg (blastocyst). See below.
Menstruation
The high levels of oestrogen and progesterone exert a negative feedback on the
pituitary inhibiting the release of the hormones FSH and LH. As a result the corpus
luteum degenerates and progesterone secretion is reduces and then stops.
With no hormone to maintain the endometrium the lining breaks down and is shed in
a process termed menstruation. Days 1 to 5 of the menstrual cycle.
The detached tissue and blood pass out through the vagina as menstrual flow for 3
to 7 days.
Learning activity 8
Ovary structure, gametogenesis and differences between gametes
174
Question 1: Ovary structure
The following photographs, 1 and 2, show sections through an ovary. Supply labels
for the parts numbered 1 to 5. You will have to think and refer to the text!
[9]
Photograph 1
Photograph 2
Question 2: Differences between spermato-genesis and oogenesis
Supply answers for the missing words, (a) to (c).
Spermatogenesis Oogenesis
Production time approximately (a) approximately (b)

___________ _________
Stage of life for from puberty onwards from puberty until (c)
gametogenesis ___________
Type of meiosis symmetrical asymmetrical
Nourishment of developing cells of cytoplasm and fluid of

gametes (d)______________ follicle
Storage of gametes stored in (e) not stored

_______________
[5]
Question 3: Differences between sperm and eggs
Supply answers for the missing words in the spaced provided on the next page.
Sperm Eggs
Size Very (a) ______ (0,05 mm), Large (b) ______ structure (0.2
looks like a tadpole Little mm in diameter) Lots of (c)
cytoplasm _____
Numbers (d) ______ produced from One made every (e) ______
175
produced puberty onwards. from puberty to (f) ______
Motility Swims by means of a tail (g) ______
Nourishment Supplied by the nutrients in Has its own cytoplasm

semen Nourished for a few days by
surrounding (h) __
Fertile period For an average of (i) ______ For (j) ______ hours after (k)
hours after ejaculation ______
[11]
(a)______________
(b)______________
(c)______________
(d)______________
(e)______________
(f)______________
(g)______________
(h)______________
(i)______________
(j)______________
(k)______________
Total [25]
Menstrual cycle changes in ovary and uterus
This is a very important graph as many questions could be asked on it.
Hormonal control of menstrual cycle
The secretion of pituitary (FSH and LH) and ovarian (oestrogen and progesterone)
hormones is controlled by a simple negative feedback mechanism. The signalling
mechanism is the increased concentration of each hormone in the blood. An
increased level of one will ‘negatively’ affect or stop the release of another.
How does the process work?

176
Under the influence of FSH a primary follicle develops into a Graafian follicle and
causes the ovaries to produce oestrogen.
Oestrogen then stimulates the pituitary gland to produce LH.
LH causes the Graafian follicle to form the corpus luteum, which secretes
progesterone.
The increased progesterone and oestrogen concentrations activate a negative

feedback mechanism, which stops the pituitary glands secreting FSH and LH.
As there is no FSH a Graafian follicle will not develop and no oestrogen, and later
progesterone, will be released by the ovary.
Because of the low levels of oestrogen and progesterone the secretion of FSH, and
later LH, from the pituitary gland no longer is suppressed and the whole cycle starts
again.
This might seem complicated but if you go over it with a friend it will become
clearer.
What is menopause?
At about the age of 46 to 54 the ovaries stop producing oestrogen and

progesterone. As a result, the ovaries stop releasing eggs and menstruation no
longer occurs. At that point women are said to have reached menopause.
Menopause causes many changes in a woman, such as hot flushes and mood
changes. Post-menopausal conditions include:
atrophy (degeneration) of the reproductive organs
bone mass loss
increasing risk of cardiac disease.
To help women cope with this difficult time, some doctors prescribe low-dose
oestrogen-progesterone preparations – known as HRT (hormone replacement
therapy).
177
Learning activity 9
The menstrual cycle
Study the graphs and diagrams and then answer the questions that follow on the
next page.
1.What do you understand by the term ovulation? (3)
2.What do you understand by the term menstruation? (3)
3.1Which cells secrete oestrogen? (1)

178
3.2What evidence is there for this in the above diagrams and graph? (2)
4.Which process does A represent? (1)
5.Name the structures, 1 and 2. (2)
6.1Name the part numbered 3. (1)
6.2What hormone does B represent? (1)
7.1What is the lining of the uterus called? (1)
7.2The lack of which two hormones cause the breakdown of the uterine lining? (2)
7.3The upper layers of the uterus are shed, a process that is accompanied by
bleeding. For approximately how many days does this continue? (1)
8.Why is it possible for a woman who has not yet ovulated during her cycle, but has
sexual intercourse, to fall pregnant? (2)
[20]
9.Devise a learning diagram to illustrate the control of FSH, LH, oestrogen and
progesterone by a negative feedback mechanism.
Estimated mark [5]
10.Questions 10.1 to 10.3 refer to the accompanying diagram, which shows the
changes that occurred in a woman’s endometrium over a period of 63 days. Write
only the letter of the correct answer in the box below. (3)
10.1On which of the following dates did menstruation begin?

a. 31 January
b. 23 January
c. 2 February
d. 8 February
179
10.2The MOST likely dates on which ovulation occurred were:
a. 14 January and 14 February
b. 14 January and 18 February
c. 21 January and 14 February
d. 21 January and 18 February
10.3The MOST likely day on which fertilisation occurred was:

a. 26 January
b. 14 February
c. 19 February
Question 10.1 10.2 10.3
Answer
Total [28]
What is the difference between copulation and fertilisation?
Humans are land animals and sperm must be transferred as close to the egg as
possible. In aquatic animals sperm and ova are simply released into the water and
fertilisation is external.
Copulation (sexual intercourse or coitus) is the transfer of sperm into the vagina of
the female when the male organ, the penis, is inserted and sperm are deposited
near the cervix. Sperm in the semen must travel through the female reproductive
system if they are to find an egg. They swim up into the uterus and eventually get
into the fallopian tubes. The majority of sperm do not make it this far. The acidic
environment in the uterus is hostile for sperm and most of them die. The sperm that
do manage to get to the fallopian tube then swim towards an egg if it is present.
After copulation fertilisation is possible.

Fertilisation is the fusion of the sperm nucleus with the egg nucleus to form a
diploid cell known as zygote.
How sperm get to ovum
Note:
Copulation must occur before fertilization.
Gestation (pregnancy)
Gestation is the time between conception (fertilisation) and birth, during which
the embryo and then the foetus develops in the uterus. Usually this is about 280
days (about 40 weeks).
180
Prenatal development
1.Early development (0 to end of 2 months)

a. Fertilisation
b. Blastocyst and implantation formation
c. Embryo formation
2.Later development (3 months to birth) – the foetal stage
1. Early development
a. Fertilisation
Fertilisation occurs in the fallopian tube when the nuclei of the sperm and egg fuse to
form a zygote. See the diagrams in the next column.
As mentioned before, a sperm lives for about 48 hours and an egg approximately 24
hours.
If fertilisation does not occur within this period the gametes will degenerate.
After semen is deposited in the vagina, sperm move through the cervix, uterus and
into the fallopian tubes until they reach the egg.
The egg, surrounded by follicle cells, is sucked into fallopian tube by the action of
the fimbriae.
Fertilisation usually occurs in the top part (outer third) of the fallopian tube.
–Thousands of sperm surround the egg.
–Hydrolytic enzymes, released from the acrosomes, break down the follicle cells.
hydrolytic = splitting molecules using water
–Only one sperm penetrates the membrane of the egg; the tail is discarded.
–The nuclei of the sperm and egg fuse forming a diploid zygote.
–A fertilisation (egg) membrane forms immediately, which prevents other sperm from
entering the egg.
The process of fertilisation

181
Fertilisation
Using relevant words, trace the path that: (a) a sperm (8 to 10 facts), and (b) an egg
(11 facts) would follow from gametogenesis up to fertilisation.
b. Blastocyst formation and implantation
After fertilisation:
The diploid zygote divides immediately by mitosis to form two cells.
Each of these divides repeatedly until a solid ball of cells, the morula (resembles a
mulberry) is formed.
–The morula develops into a hollow, fluid-filled ball of cells, the blastocyst.
–The outer cells forming the wall of the blastocyst form a layer known as
the trophoblast.
tropho = relates to feeding
An inner cell mass develops from the trophoblast.
These changes take place as the developing embryo moves along the fallopian tube
towards the uterus. It moves by a combination of peristaltic waves and the rhythmic
beating of the tube’s cilia.
After a few days in the uterus the blastocyst sinks into the thickened, highly vascular
endometrium. This is called implantation and occurs about 10 days after
fertilisation.
182
Blastocyst formation
Supply the missing labels for the micrographs below, which show the sequence of
development from before fertilisation to just before implantation.
Total [4]
c. Formation of the embryo
After implantation the:
inner cell mass forms the:
–embryo (the future baby)
–amnion, a membrane that becomes fluid-filled
–yolk sac, which forms part of umbilical cord
trophoblast (later called the chorion) develops villi that grow into the endometrium to
form the placenta. See later for placenta functions.
Young embryo
The embryo develops into three layers.
183
The outer layer forms the ectoderm and the inner, the endoderm.
The mesoderm develops between the ecto– and endoderm.
All the different tissues and organs of the body will form from these three layers by
further cell division and differentiation. During this time all major organs appear. The
heart can be seen beating. The eyes, ears and nose can be seen on the large head.
Arms and legs develop and fingers and toes are visible. The embryo grows from 1.5
mm to 30 mm.
The period of differentiation is a most critical period as embryological

malformations that can lead to birth defects can be caused by:
drugs
viruses, e.g. German measles virus
environmental factors such as pesticides.
Therefore, women must be extremely careful what medications they take and what
they eat and drink during this time of differentiation, i.e. the first two to three months
of pregnancy.
The embryonic phase lasts from the third week until the eighth week after
fertilisation.
184
Embryonic development and implantation
1.The diagram below shows blastocyst development and implantation. First,

understand and learn all the new words. Then without looking up the answers fill in
the missing labels. [7]
Doing it in this way will really help you remember the topic.
Ovulation, fertilization, cell division and implantation of the blastocyst
2.Using what you have learnt from the previous pages identify the following
micrographs and fill in labels.
12
Total [19]
2. Later development – foetal period
The foetal period of gestation lasts from the ninth week to the end of the pregnancy.
During this period some differentiation does continue, but the major change is the
rapid growth of the body. This can be seen in the table below.
As the foetus approaches term (birth), bones ossify, much subcutaneous adipose
(fat) tissue is formed and antibodies enter the foetus via the placenta to fight
disease. The foetus usually turns so that its head points downwards towards the
cervix.
crown-rump length = crown of head to buttocks
Age from date of conception (Months) Crown-rump length (mm) Weight (g)
two 30 2.25
three 75 25
four 135 170
five 185 440
six 225 820
seven 270 1 380
185
eight 310 2 220
nine 360 3 150
Ultrasound images
An ultrasound is a type of technology that uses high-pitched sound waves that

cannot be heard by the human ear. The sound is bounced off a solid structure, e.g.
the embryo and foetus.
The echoes form an ultrasound or sonogram image that will enable a doctor to view
a growing foetus giving information of:
foetal age, size and growth during normal development.
an early diagnoses of any complication.
Two ultrasound images
LH – early stage of development and RH – later, when arms are well formed
Development during foetal stage
On one diagram, draw two line graphs to show crown-rump length, (A), and weight
changes, (B), from month two to month nine. Use appropriate scales, with one
vertical axis showing size and the other weight. (7)
Once it is complete, comment on the two graphs explaining your answers. (5)
Total [12]
Human development during gestation
Time after Event Diagrams, Relative size of embryo

fertilisation scans or or foetus (from Wikipedia)
ultrasound
pictures
7 days Blastocyst
Reaches uterus
10 days Blastocyst
Implantation into
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endometrium
4 weeks Embryo
4 mm In amniotic cavity
with the following
structures having
begun to form:
brain and spinal cord
heart
arm and leg buds
6 weeks Embryo
13 mm
Basic facial features
6-week scan
develop
Arms and legs start

to grow
8 weeks Foetus
30 mm Recognisable as
human foetus 10-week scan
Head nearly half

foetal size
Major organs
functioning
Arms bend at elbows
Eyelids have formed
12 weeks Foetus
(3 months)
Sexual organs
75-mm
obvious
Legs and arms grow
Reflexes – sucking
en swallowing
16 weeks Foetus
(4 months)
Ossification of
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135 mm skeleton starts 16-week scan
Skin begins to form
20 weeks Foetus
(5 months)
Fatty tissue forms
185 mm
Real hair appears on
head
Body covered by
fine, downy hair
(lanugo) and a waxy
coating (vernix)
Eyebrows,
eyelashes, nails
formed
Foot en fingerprints
formed
24 weeks Foetus
(6 months)
Fat stored under skin
225 mm
Bone marrow makes
blood cells
Foetus might be able

to survive outside the
womb after 26 weeks
During the final months of pregnancy there is rapid development of the bones,
muscles and nervous system.
32 weeks Foetus
(8 months)
Becomes plump
270 mm
Testis descend
Lanugo begins to fall

off
36 weeks Foetus
(9 months)
Lungs mature
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300 mm Antibodies enter from
mother
Body fat increases

further
Less space to move
40 weeks Foetus
(280 days)
Normally turns into a
350 mm
head-down position
for birth
What is the difference between an embryo and a foetus?
The term embryo refers to the developing zygote until 8 weeks. During this time all
the organs of the body are being formed by differentiation.
After the organs have developed, from nine weeks until birth, it is known as a foetus.
Growth and organ specialisation takes place during this time.
Diagram of the young foetus
The placenta
The placenta is a disc-shaped temporary organ richly supplied with maternal and
foetal blood vessels. It connects the foetus with its mother’s blood at the end of the
umbilical cord.
As mentioned the placenta develops from the chorion and its villi that penetrate the
endometrium. The villi provide a large surface area of attachment of the placenta to
the endometrium. Each villus contains a capillary network, which provides a large
surface area for exchange of substances by diffusion. The placental villi are
surrounded by the mother’s blood, so that mother’s blood supply and foetal
capillaries are very close to each other. However, the foetal and mother’s blood do
not mix because the foetal capillaries have thin walls. Substances move between
the maternal and foetal blood by diffusion. If the blood mixed, it could cause the
foetal blood to clot, resulting in the death of the foetus.
Functions
1.Oxygen and dissolved food substances such as glucose, amino acids, fatty
acids, ions and vitamins pass from the mother to the foetal blood system for
respiration and nutrition.
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2.Foetal waste products of metabolism, e.g. urea and carbon dioxide pass into
the maternal blood system for excretion.
3.Some maternal antibodies pass to the foetus providing temporary passive

immunity to certain diseases. As a result the child enjoys immunity to most infectious
diseases during the first six months of life.
4.The placenta acts as a barrier (micro filter) preventing many pathogenic (harmful)
micro-organisms and drugs from entering the foetus from the mother. However,
some pathogens can pass through the placenta, e.g. those causing German
measles (rubella), syphilis and HIV.
5.The placenta also has an endocrine function.
After three months of pregnancy the placenta takes over the function of
secreting progesterone and oestrogen from the ovaries (corpus luteum). These
hormones are essential for bringing about the necessary changes in the uterus and
for the maintenance of pregnancy.
Progesterone prevents ovulation and menstruation which would result in the loss of
the foetus.
Late in pregnancy it secretes relaxin, a hormone that relaxes joints and ligaments to
assist in the delivery of the baby.
In early pregnancy the placenta secretes human chorionic gonadotropin (HCG). This
is the basis of many pregnancy tests.
Note:
Harmful substances such as cigarette smoke (carbon monoxide and nicotine),

alcohol, illegal drugs and many medicines can pass though the placenta and
can cause significant damage to the developing embryo and foetus.
Diagram to show the relationship of the placenta to the foetus and the
endometrium
Placenta functions
Devise a clear, simple diagram to show these functions.
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The amnion
The amnion is a membrane that surrounds the developing embryo and foetus. It
secretes a fluid called amniotic fluid that fills the amniotic cavity.
What is amniotic fluid?
Amniotic fluid surrounds the developing foetus and serves to provide a protective
environment. It consists of about 99% water, foetal cells and waste products.
The cells contain foetal genetic information. This is why amniotic fluid is used during
a process called amniocentesis to determine whether the baby has any
chromosomal abnormalities.
Functions
Amniotic fluid is essential for the developing foetus. It performs the following
functions.
1.It supports the developing foetus, allowing it freedom to move about easily and so
prevent malformations due to gravity/pressure.
2.It cushions and protects the foetus from damage by external injury or from impact
from the mother.
3.It provides a medium in which to practice breathing and swallowing movements.
4.It holds urine as it is released from the foetus.
5.It protects the foetus against:
changes in temperature
dehydration.
Functions of amniotic fluid
Devise a clear, simple learning diagram to show the functions of amniotic fluid.
191
Umbilical cord
The umbilical cord of the foetus is a flexible cord extending from its abdomen to the
placenta. It joins the foetus to its mother and contains two umbilical arteries and a
single umbilical vein.
Functions of the umbilical cord
The umbilical cord contains blood vessels, the:
1.umbilical arteries, which leaves the foetus carrying waste, eg carbon dioxide and
other excretory waste products. These substances diffuse into the mother’s blood
and are excreted.
2.umbilical vein, which enters the foetus carrying oxygenated blood and nutrients
(such as glucose and amino acids) from the mother.
Stages of pregnancy
Pregnancy lasts nine months and is divided into three periods or trimesters, each
about three months.
First trimester
The first 12 weeks of pregnancy are considered to make up the first

trimester. During this time the risks of miscarriage and birth defects are highest.
Changes
Hormonal changes affect almost every system in the body.
The menstrual period stops, which is a clear sign that a woman is pregnant.
A pregnant woman can also experience tiredness, cravings or distaste for certain
foods and have mood swings.
Nausea or morning sickness, which can occur at any time of the day, occurs in about
seventy percent of pregnant women.
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The breasts become tender and swollen with the nipples and areolas becoming
darker.
Second trimester
Weeks 13 to 28 make up the second trimester.
Changes
Most women have more energy in this trimester.
The symptoms of morning sickness lessen and eventually disappear.
The uterus, the muscular organ that holds the developing foetus, starts expanding.
By the end of the second trimester, the expanding uterus has created a visible ‘baby
bump’. During pregnancy it expands up to 20 times its normal size.
The movement of the foetus, often referred to as ‘quickening’, can be felt. This
typically happens in the fourth month (16 weeks).
Patches of darker skin can appear on the face; sometimes called the ‘mask of
pregnancy’.
Third trimester
Weeks 29 to 40 make up the third trimester. In the photographs one can see the
comparison of growth of the abdomen between 26 weeks (second trimester) and 40
weeks (third trimester) of pregnancy.
Changes
Final weight gain takes place, which is the most weight gain throughout the
pregnancy. The foetus will be growing the most rapidly during this stage, gaining up
to 28 g per day.
The pregnant woman feels the more frequent and stronger movements of the foetus,
which can be disruptive.
Many women find breathing difficult as the foetus presses up against the diaphragm
and lungs.
In the final weeks the woman's abdomen changes shape as it drops down quite low
due to the foetus turning in a downward position ready for birth. The foetal head
descends into the pelvic cavity – this is known as engagement of the head. As a
result there is:
–less pressure on the upper abdomen and breathing becomes easier.
–reduced bladder capacity which can result in weak bladder control.
–often backache.
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The breasts can become tender and may leak a watery pre-milk fluid called
colostrum.
Sometime during the third trimester, the muscles of the mother's uterus starts
contracting. These Braxton-Hicks contractions are practice to help the mother's body
prepare for labour. Frequent or painful contractions could be a sign of real labour.
Gestation
1.Where in the woman’s reproductive system does conception occur? (1)
2.List any two early symptoms of pregnancy. (2)
3.Discuss the effect that pregnancy has on the mother. What are some of
the physiological changes experienced by the mother during pregnancy?
(5) Answer carefully!
4.What is the difference between an embryo and a foetus? (3)
5.Describe as fully as you can what you observe from the photograph below. (5 x 2 =
10)
6.What is the normal length of pregnancy? (1)
7.What is the term for the position of unborn baby where the back is curved, the
head is bowed, and the limbs are folded up against the torso. (1)
8.At what point in the pregnancy does a woman begin to feel foetal movement? (1)
9.When is the risk of a miscarriage the greatest? (1)
Total [25]
Birth (parturition)
Birth is the expulsion of the foetus, its surrounding membranes and the placenta
from the uterus.
Approximately nine months after fertilisation the baby is ready to be born. What
actually starts the birth process, even after decades of research, is unclear. What is
known, however, is that at the end of the gestation period the placenta is less
efficient. For this reason alone birth must take place.
What is distinctive about birth in humans?
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The human baby is born at a relatively immature and very helpless stage. If the
human foetus grew any larger it would not be able to leave the body successfully for
the following reasons.
–In the process of becoming upright and bipedal, the pelvis had to be narrower in
humans, which also made the birth canal narrower than any other primate or
mammal.
–The brain, even in the foetal stage, is much larger than that in other primates. If it
enlarged any more the head would not be able to pass through the birth canal.
The baby is usually born headfirst; the head circumference of the baby at (or before)
birth is the largest diameter of its body.
How does birth occur?
Two or three weeks before birth the foetus moves into position for birth. For a normal
birth to take place, the foetus must lie with its head pointing downward towards the
cervix.
Just before the baby is born, the very high levels of oestrogen in the mother’s blood
cause the hypophysis to release a hormone called oxytocin. This hormone
promotes contraction of the uterine wall.
The entire birth process may take from a few hours to well over a day. There
are three stages.
1. Dilation of the cervix
During this stage the myometrium starts contracting. Contractions are at first slow
and rhythmic but later become intense and more frequent.
The uterine muscle contractions:
force the amnion and foetus towards the cervix.
cause the cervix of the uterus to dilate.
About the time that the cervix becomes fully dilated (about ten centimetres) the
increased pressure causes the amnion to break and release amniotic fluid, which
passes out through the birth canal (vagina). This is commonly called ‘breaking of the
waters’.
2. Delivery of the baby
After the cervix is fully dilated the baby is pushed out through the vagina, usually
head first, by the very powerful contractions of both the uterine and abdominal
muscles. Immediately after birth the umbilical cord is tied and cut. The part of the
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umbilical cord still connected to the baby shrivels up and becomes its navel or belly
button.
Note:
The passage of the head through the birth canal is made easier by the fact that the
flat bones of the baby’s skull are separated by connective tissue and are not fused.
This allows the head to change shape, called moulding, allowing the baby’s head to
pass through the birth canal. The often misshapen head of the new-born quickly
returns to normal.
Diagram to show birth of a baby
3. Expulsion of the placenta
The final stage happens about ten to twenty minutes after delivery when the placenta
with the remaining bit of the umbilical cord comes away from the uterine wall. Uterine
contractions will force it out as the afterbirth. This stage of labour is short, seldom
lasting longer than 15 minutes.
Birth options
There are different birth options:
Vaginal childbirth – natural (drug-free) or with pain medication
Cesarean section - if a normal birth puts the life of the mother or her baby at risk or if
there are complications (e.g. awkwardly positioned baby) a woman may have her
baby delivered by Caesarean section (C-section). This involves cutting open the
abdomen and uterus of a woman, removing the baby from the uterus and stitching
up the cut.
Stages of childbirth
The following stages of normal childbirth have been mixed up. Write down the
correct order of the numbers.
1.Amnion and chorion bursts
2.Placenta expelled from the uterus
3.Contractions of the uterine wall
4.Baby’s head comes out from vagina
5.Amniotic fluid expelled
6.Cervix dilates
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Total [6]
What are mammary glands?
Mammary glands are organs in female mammals that produce milk to feed young
offspring. In humans, the mammary glands are situated in the breasts and are made
up of milk-secreting cells.
What is lactation?
Mammary gland
During pregnancy oestrogen and progesterone stimulate the growth and

development of the milk glands and milk ducts in the breasts.
After birth prolactin from the pituitary gland stimulates the mammary glands to
produce milk.
A second hormone, oxytocin, from the hypothalmus, causes the release (flow) of
milk from the glands.
Breast milk is favoured above bottle feeding because it:
–contains antibodies which can help a baby fight infections
–contains all the nutrients in perfect proportions for optimal growth
–is cheap and easy, as there are no bottles to sterilise or tins to buy.
Did you know?
The sequence of physical development in every normal, healthy infant happens on

its own and does not need any interference from the parents.
Hugs and cuddles help babies to become more intelligent.
If the young have negative experiences, e.g. are abused or neglected, left in front of
a TV or get no stimulation their brains can actually be smaller than other children
their own age.
Being a parent is a great responsibility, isn’t it?
Birth control (Contraception)
Contraception is the prevention of fertilisation when sexual intercourse takes

place. All towns have Family Planning clinics where free advice and help is given.
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Although there is no single, ideal method of birth control, several types of
contraceptive methods are available, each with its own advantage and
disadvantages. The only method that is 100% sure is abstinence, i.e. not having
sexual intercourse. Every baby must be a wanted baby.
How do contraceptives work?
Contraceptive devices can be divided into three main groups according to how they
work.
1.Prevent egg being released, i.e. prevent ovulation
2.Prevent sperm reaching egg, i.e. prevent fertilisation
3.Prevent embryo implantation or development
4.Other methods
1. Prevent ovulation
The pill
The birth control pill is one of the most commonly used contraceptive products. It is
very reliable provided it is taken every day, and the instructions are followed very
carefully. The pill contains minute amounts of oestrogen and progesterone and is
taken daily, except for the last 5 days of the 28-day cycle.
These two hormones prevent ovulation. With no egg being released pregnancy
cannot occur.
2. Prevent sperm reaching egg
Sterilisation
Sterilisation usually is permanent so individuals who plan to have more children do

not use it. The advantages are that it does not affect the reproductive physiological
processes, is not harmful and is cheap.
Sterilisation
Male sterilisation is called a vasectomy. The sperm duct is cut, preventing the
sperm from being expelled. The sperm that are made, after a while, are broken down
and absorbed back into the body.
Sterilisation in females is achieved by performing a tubal ligation. The fallopian

tubes are tied off, which prevents the egg and sperm from meeting.
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Condom
A condom is a barrier device used during sexual intercourse to reduce the

probability of pregnancy and spreading sexually transmitted diseases (STDs) such
as gonorrhoea, syphilis, and HIV.
a. Male condom
The condom is a non-porous, very strong rubber sheath. The condom fits over an
erect penis and must be put on before sex begins. It catches the sperm and stops it
from getting into the vagina.
Properly used, a condom is an excellent and reliable method of contraception,

especially if it is combined with a spermicide. See below.
It also has the great advantage of preventing not only sperm, but also viruses and
bacteria from passing between the man and woman. Condoms, therefore, should be
used for safe sex because they help to prevent the spread of sexually transmitted
infections (STDs).
Male condom
b. Female condom
This contraceptive device, known as FemodomTM, is similar to a small, elongated

balloon. It fits inside the female and lines the vagina. Its added advantage is that it
gives women a means of protecting themselves against STDs.
Female condom
Spermicide
Spermicides are chemicals that kill sperm. Spermicides (creams, foams or gels)
are put in the vagina and are often used with condoms. If they are used on their own
they are not very effective at preventing pregnancy.
3. Prevent embryo implantation or development
MAP (morning-after-pill)
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This is a course of pills, e.g. ‘Ovral 28’, which must be started within 72 hours of
unprotected intercourse.
The oestrogen-progesterone combination completely confuses the normal hormonal

signals. As a result, either fertilisation is prevented or a fertilised egg cannot implant.
Intrauterine devices (IUDs)
An intrauterine device (IUD), a small object made of plastic, copper or stainless

steel, is inserted into the uterus. It prevents implantation of the blastocyst and is
recommended for women who have already given birth. It is a fairly reliable method
of contraception.
Intrauterine device
RU 486 (mifepristone)
Another pill uses a substance called mifepristone (RU486). It must be taken within
the first 7 weeks of pregnancy. It blocks the action of progesterone so that if
implantation has occurred the endometrium will disintegrate resulting in a
miscarriage. It has a success rate of between 96% and 98% with virtually no side
effects.
4. Other contraceptive devices
Injectables, e.g. three-month injection
An injection, Depo-Provera, which lasts for three months, is the most commonly
used method of contraception and is recommended for teenagers. It is stored in
the liver and contains synthetic progesterone that is released slowly. Nur Isterate
works by:
paralysing the fallopian tubes, so they cannot carry the egg to the uterus.
making cervical mucus thick and impenetrable to the sperm.
making the endometrium unsuitable for implantation.
Injectable contraceptives are easy, mainly because one does not have to remember
to take precautions against falling pregnant.
Withdrawal
This is definitely not recommended as it is a very easy way to fall pregnant. It

refers to the withdrawal of the penis from the vagina just before ejaculation.
Contraception
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The table below shows the use of different types of contraception as a percentage of
the total used by the South African population.
Method of contraception % of total use
Injectables 41.0
Pill (oral) 12.3
Condom 2.1
Female sterilisation 12.0
Male vasectomy 1.7
Intrauterine device (IUD) 1.9
Withdrawal 5.0
Other 24.0
Source: Department of Health and Family Planning
1.According to the above information which method is:
1.1most commonly used? (1) ___________
1.2least commonly used? (1) ___________
2.Disregarding its role as a method of contraception, why should a condom (male

and female) be used, particularly when sexual intercourse is not restricted to one
partner? (2)
3.What will be missing from the semen of males who have had a vasectomy? (1)
4.Will a female who has been sterilised continue to produce:
4.1eggs __________________________
4.2oestrogen and progesterone? (2) ______
5.What method is usually recommended by the Family Planning clinics for

teenagers? (1)
6.What method is very likely to result in pregnancy? (1)
7.What method of contraception would be most suitable for a couple who have all
the children they want? (1)
8.Apart from falling pregnant and possible effect of the pill on the medical health of
women, discuss why you think the birth control pill has not been a good thing. (2)
Total [12]
Know your rights
Learn about contraception
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Knowledge is power. The more you know about reliable and effective contraception
options, the better your chances are of preventing an unplanned pregnancy or STI.
Show respect for yourself and your partner by obtaining accurate information
about contraception before you have sex.
Using reliable and effective contraception in the way it is intended is the most
effective way of preventing an unplanned pregnancy.
Sexually transmitted infections
Sexually transmitted infections (STIs) or sexually transmitted diseases (STDs) are

passed from one person to another though unprotected sex. They can affect the
general health and fertility of the people who have them. STIs are caused by micro-
organisms such as viruses, bacteria and fungi.
Anyone who has sex has a chance of getting infected with an STI and the more
sexual partners he or she has, the greater the chance of getting infected.
The incidence of STIs is highest between 15 to 29 years and is usually the result of
multiple partners.
While in many instances STIs are not life threatening, they are extremely dangerous
as they weaken the body’s defences, making it much easier for the HI virus to
enter the body. HIV/AIDS is the most serious of all the STIs.
Examples of STIs are:
HIV/AIDS, genital warts and genital herpes (caused by viruses)
gonorrhoea and syphilis (caused by bacteria)
thrush (caused by fungi).
1. Human immune-deficiency virus
HIV/AIDS is caused by a virus. The human immuno-deficiency virus (HIV) is passed

from one person to another through the transfer of body fluids such as semen or
vaginal fluids during sexual intercourse, blood during blood transfusions and milk
from an infected mother who is breastfeeding her baby.
Micrograph of HIV viruses
HIV attacks the body’s immune system making it difficult for an infected person to
fight off other diseases and infections. As the body’s immune system gets weaker
and weaker, a condition called Acquired Immune Deficiency Syndrome (AIDS)
develops.
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What are some symptoms of AIDS?
loss of appetite
rapid loss of weight
diarrhoea lasting longer than a month
tiredness and headaches
memory loss
persistent cough
sores and rash on the body
A person with AIDS also becomes infected with other diseases, such as tuberculosis
and pneumonia, which the body’s weakened immune system cannot fight off. It is
usually one of these diseases that is the cause of death of someone with AIDS.
How can HIV/Aids be treated?
HIV-positive people can be treated with anti-retroviral (ARV) drugs. These drugs can
prevent the onset of AIDS and these people can live healthy, active lives.
Unfortunately these drugs are not always available to people living in poor countries.
Without ARV drugs, HIV-positive people usually develop full-blown AIDS within 10
years.
Even if an HIV-positive person responds well to ARV drugs, they still have the virus
and must remember to act responsibly if they decide to have sex. Such a person
might appear to be fit and healthy but can still infect his or her partner if they decide
to have unprotected sex.
What are some of the social consequences of HIV/AIDS?
The socio-economic consequences of HIV/AIDS in southern Africa are very serious.

Southern Africa has the highest percentage of people infected with HIV in the world.
In some parts of southern Africa, more than a third of the people are HIV-positive,
many of them with full-blown AIDS.
People who are HIV-positive or who have AIDS are often treated badly by other
people in the community.
People spend more and more time caring for sick family members.
Families suffer as they lose loved ones. Older people may lose their children and
grandchildren, and children may lose their parents.
Families and communities cannot function as before as it is often the young and
middle-aged adults who die from AIDS. These are the people who would normally be
supporting their families and communities.
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What are some of the economic consequences of HIV/AIDS?
Many young people do not have access to education and development that they
need in order to become economically productive members of society because they
are too busy caring for sick relatives or their younger siblings.
As families lose their breadwinners, there is financial hardship as less money is

available for food, accommodation, clothes and education.
The healthcare system is put under a lot of strain as there is often not enough money
to provide the treatment needed for all the sick and dying patients.
Local economies suffer as there are not enough skilled workers to run businesses,
schools and hospitals.
2. Syphilis
Besides Aids, syphilis is a common sexually transmitted infection. It is caused by a

bacterium that enters the body through tears in mucous membranes in the genital
areas.
How does infection take place?
Syphilis is spread:
most often by direct sexual contact with a person who has an active infection.
by being passed on to a foetus during pregnancy.
How is syphilis diagnosed?
In the primary stage, symptoms of syphilis are easily missed so an early diagnosis is
difficult. Diagnosis is by blood tests that test for antibodies to the bacteria that
cause syphilis. Because the symptoms of syphilis are so varied, it is wise to test any
person with possible signs of syphilis.
Note:
All pregnant women must be tested. Those infected could then be successfully
treated to prevent the unborn child contacting syphilis.
What are symptoms of syphilis?
Soon after infection a small bump appears on the penis, vagina or cervix. This
gradually turns into a painless sore or ulcer that disappears after a few weeks. This
stage may go completely unnoticed, which results in the spread of this sexually
transmitted disease, as people in the primary stage of syphilis are very infectious.
The second stage is characterised by similar sores, a skin rash on other parts of the
body and possibly a mild fever.
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Syphilis rash
The third stage may occur ten or more years after infection. The bacterium by this
time will have invaded most parts of the body, and will begin to cause damage to
many organs such as the liver, bones, blood vessels and the nervous system.
Treatment
It is easily and successfully treated with antibiotics. The infection can be fatal if not
treated.
In the past, devastating epidemics of syphilis caused the deaths of thousands of

people, including King Henry VIII of England.
Syphilis caused the death of henry VIII
3. Gonorrhoea
Gonorrhoea is probably the most common STI. It is caused by a bacterium and is

very infectious. The bacterium lives and breeds in the moist, warm linings of the
reproductive and urinary tubes and cavities. Gonorrhoea infection takes place most
often by direct sexual contact with a person who has an active infection.
What are the symptoms of gonorrhoea?
This disease usually first appears in the genital areas but can affect many other body
parts.
Females
In women gonorrhoea most often starts as an infection in the cervix. Unfortunately,

50 to 60% of women with gonorrhoea do not know they have the infection as they
have no symptoms.
Symptoms in a woman can include the following:
painful urination and/or pain during intercourse (this is because the urethra and/or
vagina is infected and inflamed by the bacteria).
a cloudy, yellowish vaginal discharge.
Males
About 85% of infected men have symptoms that develop within two to ten days of
being infected.
The main symptom is a yellowish urethral discharge, often with very painful urination.
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Sometimes the testicles are painful.
Treatment
It is easily treated with antibiotics. If not treated it could lead to serious complications.
It is important to:
re-test the infected person once the antibiotic course is finished to ensure the
infection is cured.
treat all sexual partners of the infected person.
abstain from sexual activity until gonorrhoea has cleared up.
What are the complications?
The infection can spread throughout the female reproductive tract resulting in pelvic
inflammatory disease. This can cause great damage to the reproductive organs, and
may lead to infertility.
In pregnant woman there is an increased risk of an ectopic pregnancy, a miscarriage

or premature birth.
During childbirth the bacteria may pass from a mother to her baby, this could lead to
pneumonia or a serious eye infection that can cause blindness in the baby.
Re-infection with gonorrhoea is common.
Avoiding or preventing the transmission of STIs
We have to make responsible choices about our sexual behaviour to avoid getting
infected with STIs.
We can choose to abstain from sex. People who do not have sex will not become
infected with STIs.
We can choose to abstain from alcohol and drugs. People who drink or take drugs
are far more likely to take risks or make irresponsible choices about sex.
We can choose sexual partners carefully.
We can choose to be faithful, i.e. have a monogamous relationship. If two people

who are not infected with an STI have sex only with each other and nobody else,
then they will not get infected with an STI.
We can choose to use a condom. Condoms prevent people coming into contact with
the semen or vaginal fluids of an infected partner, which reduces the chances of
becoming infected with an STD.
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We can choose not to ignore symptoms and get treated immediately if an infection is
suspected; and telling previous sex partners, if one has an infection, so they can go
for treatment if necessary.
Sexually transmitted infections
Question 1
1.What does STI stand for? (1)

_______________________________________________________
2.How could the spread of gonorrhoea from mother to baby be prevented? (1)
_______________________
3.Why is it easier to be infected by the HI virus if you have an STI? (1)

_____________________________
Question 2
Complete the following table on two sexually transmitted infections. Use only one
word or term for each factor or idea. Educator must decide on how to assess this
activity.
Syphilis Gonorrhoea
Cause
Site of infection
Method of infection
Symptoms
Treatment
Complications
Prevention
Question 3
State whether the statements are true or false:
1.Women who have had gonorrhoea are more likely to be infertile. _________
2.Men under 25 are at greater risk for STIs than are women. ____________
3.Self-consciousness is a big obstacle people have when trying to protect

themselves against STIs. ___________
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4.When women have gonorrhoea there are usually no symptoms. __________
5.Condoms are still the best form of protection against contracting STIs. _________
[5]
Question 4
1.Why do you think it’s unlikely that one can contract gonorrhoea from a toilet seat?
(2)
2.Why do you think a baby could test positive for syphilis but does not in fact have
the disease?
(2) This question relates to the section on immunity.
Total (Questions 1, 3 and 4) [12]
Infertility
Couples who have been trying to conceive a baby for more than a year and who
have not been successful may have to accept that one or both of them is infertile.
There are many reasons for infertility and many solutions for the different problems.
Apart from the reasons given below a man or woman’s lifestyle may also affect his or
her fertility such as stress, diet, age, alcohol, drugs, cigarettes, medicines etc.
Male infertility
Diagnosis of male infertility begins with seeing what medications might be being
taken, a physical examination and the testing of several semen samples.
What are possible causes of male infertility?
In most infertile men, the problem is in the testis, the glands that produce sperm and
testosterone.
Damage to the testis can be as a result of mumps, radiation or chemotherapy,

trauma or surgery.
Testicular damage can lead to:
a low sperm count, i.e. not enough sperm are produced.
poor sperm quality, e.g. sperm do not move well or are abnormally shaped.
Sometimes the sperm ducts can be blocked due to an infection. This will prevent
sperm exiting during an ejaculation.
Most cases, however, have no identifiable cause, even after an assessment.
Treatment
208
If sperm counts are too low due to incorrect levels of male hormones then LH and
FSH hormone injections are given. This treatment is usually successful; however, it
may take a year or longer to bring back fertility. This treatment is expensive.
Surgical intervention can be attempted to clear blocked sperm ducts.
Female infertility
What are possible causes of female infertility?
In females there might be:
problems with ovulation when viable eggs are not made.
blocked oviducts that prevent egg and sperm from meeting.
problems with the uterus, e.g. fibroids (lumps that develop from the myometrium),
which can prevent the implantation of blastocyst.
How can female sterility be treated?
Fertility treatments can be grouped into three categories – fertility drugs, surgical
treatment and assisted conception.
Fertility drugs remain the primary treatment for women with ovulation disorders;
some are taken orally and some are injected. In general, these medications work by
causing the release of hormones that either trigger or regulate ovulation.
Surgical treatments, e.g. unblocking fallopian tubes, removing fibroids and clearing
up endometriosis.
endometriosis = a disease in which tissue that normally grows inside the uterus
grows outside the uterus
Assisted conception. This includes several techniques such as:
–artificial insemination
If a man is unable to produce viable sperm, a solution is to use sperm from a sperm
donor.
The sperm donor may be anonymous, from a sperm bank, or a close male relative.
Semen from the donor is inserted into the woman’s vagina at the time she is
ovulating.
–in vitro fertilisation (IVF)

If a woman is unable to produce viable eggs a solution is to use eggs from an egg
donor.
The egg donor may be anonymous or a close female relative.
Eggs are removed from the egg donor and fertilised by sperm from the woman’s
partner, outside the body. This is known as in vitro fertilisation (IVF).
209
The fertilised eggs are then placed in the uterus of the woman and left to implant in
the endometrium.
Other assisted conception techniques include: gamete intra-fallopian transfer (GIFT)

and intra-cytoplasmic sperm injection (ICSI).
Assisted conception fertility treatments are very expensive and many people simply
cannot afford them.
Surrogacy
What is a surrogate?
A surrogate is a woman who carries a baby on behalf of future parents who are
medically unable to do so.
The process is done either by artificial insemination from the man (commissioning
father) or implantation of an embryo from the woman (commissioning mother)
formed by the IVF technique. This means that the embryo and resulting baby will not
be genetically related to the surrogate mother at all.
Surrogacy is 100% legal in South Africa and is governed by a complex set of

guidelines to protect the rights and well-being of all parties involved (the surrogate
mother, the commissioning parent(s) and the unborn baby/babies.
The guidelines include the following.
No surrogacy action may commence unless a high court application has granted its
approval.
Included in the documents that are required for this are:
–Psychological reports for surrogate mother and commissioning parents.
–Medical report for commissioning parents with proof that they are unable to achieve
a pregnancy for themselves.
–Social worker’s report for surrogate and commissioning parents.
Surrogacy may not be done for commercial gain. The surrogate may only claim for
loss of income and other expenses incurred as a direct result of the
surrogacy/pregnancy.
The surrogate surrenders any parental rights.
Foetal alcohol syndrome
Foetal alcohol syndrome (FAS) is a pattern of birth defects, learning and

behavioural problems affecting children whose mothers consumed alcohol during
pregnancy. FAS is the most common preventable cause of mental retardation.
210
South Africa has the highest reported incidence in the world of babies being born
with FAS every year. It is estimated that currently there are 2 million South Africans
with FAS.
During pregnancy the alcohol freely crosses the placenta and causes damage to the
developing embryo or foetus. Alcohol use by the father cannot cause FAS.
What are some features of FAS?
Classic physical features of FAS in new born babies include:
short stature
low birth weight
poor weight gain
microcephaly.
Other features become evident as the child gets older. Such abnormalities include:
poor attention span
poor motor skills
slow language development
hyperactivity disorder
learning disabilities or mental retardation, e.g. memory problems, poor judgment,

difficulties with abstract reasoning skills
poor social skills.
There is no treatment for the effects on the mental processes. These children will
remain mentally and socially defective all their lives.
Much education needs to be done to get the essential message across to the public.
Don’t you agree that FAS is a tragic condition? The action of the mother directly
affects her unborn child.
If you are pregnant don’t drink, if you drink don’t get pregnant.
Short questions
1. Multiple choice
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
1.The testis are protected by the: (a) epididymis; (b) prostate gland; (c) scrotum;
(d) spermatheca.
2.Before copulation the male sperm is stored temporarily in the: (a) seminal vesicles;
(b) scrotum; (c) prostate gland; (d) epididymis.
3.During a single ejaculation of semen from the penis: (a) only 2 sperm are released.
(b) more than 500 000 000 sperm are released. (c) 6 sperm are released. (d) 23
sperm are released.
4.How many functional chromosomes are there in a somatic cell of a male person?
(a) 45; (b) 46; (c) 23; (d) 47.
5.The process whereby male gametes are formed is known as: (a) spermatogenesis;
(b) oogenesis; (c) mitosis (d) fertilisation.
6.Which one of the following is wrong with reference to the number of

chromosomes? (a) zygote = 2n; (b) gonads = n; (c) embryo = 2n; (d) gametes = n.
Questions 7 to 10 refer to the following diagram of a section through an ovary.
7.Which of the following is the correct sequence in the development of the labelled
structures? (a) AFEDCB; (b) EFBCDA; (c) CDBAFE; (d) BCEFAD.
8.Which process is occurring at F? (a) oogenesis; (b) fertilisation; (c) ovulation;

(d) menstruation.
9.Which of the following structures does the letter F represent? (a) primary follicle;
(b) Graafian follicle; (c) germinal epithelium; (d) corpus luteum.
10.Which of the following structures does the letter A indicate? (a) primary follicle; (b)
Graafian follicle; (c) corpus luteum; (d) secondary oocyte.
11.An unfertilised egg can survive in the fallopian tubule for: (a) six hours; (b) four
days; (c) one or two days; (d) thirty minutes.
12.Menstruation occurs: (a) 28 days after ovulation. (b) 14 days after ovulation. (c) 7
days after ovulation. (d) 10 days after ovulation.
13.The normal menstrual cycle takes: (a) 32 days; (b) 1 day; (c) 28 days; (d) 0 days.
14.Fertilisation takes place in: (a) the infundibulum of the fallopian tubes. (b) the
fallopian tubes. (c) the uterus. (d) in the cervix.
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15.Fertilisation takes place when the: (a) sperm enters the egg. (b) sperm comes
into contact with the egg. (c) nucleus of the sperm combines with the nucleus of the
egg. (d) fertilisation membrane is formed around the egg.
16.Progesterone: (a) prepares the uterine wall for implantation of the embryo
(blastocyst). (b) speeds up the development of follicles. (c) brings about the
formation of corpus luteum. (d) stimulates the secretion of sweat.
17.Which of the following cannot pass through the placental barrier? (a) blood cells;
(b) glucose; (c) amino acids; (d) antibodies.
18.The fluid surrounding the embryo is: (a) semen; (b) chorionic fluid; (b) lymph; (d)
amniotic fluid.
19.During the development of the embryo the function of the amnion is: (a) to serve
as reserve food. (b) to give rise to the placenta. (c) to prevent the developing foetus
from moving about. (d) to hold the fluid which protects the embryo against injury.
20.The period of gestation (from fertilisation to birth) is: (a) 280 days; (b) 310 days;
(c) 20 days; (d) 210 days.
[20]
2. Terms
Statement Term
1.The production of male gametes in the testis.
2.A highly convoluted tubule in which the spermatozoa mature and are
stored.
3.A muscular duct which conveys the sperm into the abdominal cavity.
4.The gland at the base of the bladder.
5.The process whereby eggs are formed from oocytes.
6.The hormone secreted by Graafian follicles.
7.The rupturing of a mature Graafian follicle to release an egg.
8.The remains of the Graafian follicle in the ovary after ovulation.
9.The shedding of upper layers of endometrium fourteen days after
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ovulation.
10.The hormone responsible for development of endometrium for

implantation.
11.The tissue complex responsible for the nutrition and respiration of the
embryo.
12.The structure attaching the embryo to the wall of the uterus.
13.The embryo after two months in the uterus.
14.The innermost membrane which protects the embryo in the uterus.
[14]
3. Mix and match
Match each description in Column A with an item in Column B. Write the letter next
to the relevant number.
1. Male hormone 1. A. epididymis
2. Stage of development at implantation 2. B. penis
3. Site of fertilisation in humans 3. C. puberty
4. Protection of the foetus 4. D. testosterone
5. Storage of sperm 5. E. fallopian

tube
6. Transference of sperm to the vagina 6. F. myometrium
7. Inner lining of uterus 7. G. blastocyst
8. Contains hydrolytic enzymes 8. H. semen
9. Spermatozoa and seminal fluid 9. I. endometrium
10. A muscular layer 10. J. amniotic fluid
11. An organ enclosed by the scrotum 11. K. testis
12. Series of physical changes initiated by the 12. L. acrosome
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hormone FSH
[12]
In each case, write down if the statement is true or false. If false, write down the

word word
1.The only sure way of birth control is abstinence.
2.Ovulation involves the release of a ripe egg from an

ovary (Graafian follicle).
3.Fertilisation takes place in the upper region of the

uterus and involves the fusion of the male gamete
nucleus with the female gamete nucleus.
4.Contraceptive practices affect fertility by increasing

the probability of conception.
[4]
Total [50]
Life at molecular, cellular and tissue level
DNA – the code of life
Nucleic acids have been called the ‘molecules of life’ or the ‘most extraordinary
molecules on earth’ as they have the capacity to store the information that controls
cellular activity and the development of an entire organism. They do this
by controlling the synthesis of proteins. Making proteins may seem a far cry from
making an entire organism, but it is the first step in that direction. Proteins not only
make up much of the structure of the body but, as enzymes are proteins, they also
control the chemical processes inside cells. In this way they ultimately control the
structure and functioning of all living organisms.
The two nucleic acids found in cells are:
1.Deoxyribonucleic acid (DNA)
2.Ribonucleic acid (RNA)
1. Deoxyribonucleic acid – DNA
215
DNA's discovery has been called the most important biological work of the last 100
years.
Who discovered the structure of DNA?
At King's College in London in the early 1950’s, Maurice Wilkins and Rosalind
Franklin were trying to work out the structure of DNA. They took an experimental
approach, looking particularly at X-ray crystallography, i.e. diffraction images of DNA.
At the same time at the Cavendish Institute at Cambridge University, graduate

student Francis Crick and research fellow James Watson also became interested
in determining the structure of DNA. They analyzed the x-ray data collected by
Rosalind Franklin and others. They then built a model out of brass plates and clamps
and other bits of laboratory equipment and realised that nucleic acids are arranged
like a twisted ladder, with two runners made of phosphates and sugars, and a series
of rungs made of pairs of organic compounds known as bases.
What about genetic replication?
Watson and Crick developed their ideas about genetic replication in a second
article in Nature, published on May 30, 1953. The pairing of the bases, i.e. A=T and
C=G suggested that given a sequence of bases in one strand, the other strand was
automatically determined. This meant that when the two strands separated, each
served as a template for a complementary new chain, i.e. each strand could
replicate. See page 134.
After the ‘double helix’ model there were still questions about how DNA directed the
synthesis of proteins. In 1961, Francis Crick and Sydney Brenner provided genetic
proof that a triplet code was used in reading genetic material in DNA and
transferring this information from the nucleus to the cytoplasm via RNA to where
proteins are made. More about this on page 139.
The two had shown that in DNA, form is function: the double-stranded molecule
could both produce exact copies of itself (replicate) and carry genetic instructions,
i.e. that the sequence of the bases in DNA forms a code by which genetic
information can be stored and transmitted.
Who won the Nobel prize?
Of the four DNA researchers only Rosalind Franklin had any degrees in chemistry.
She worked mostly alone and suspected, through her x-ray diffractions, that all DNA
molecules were helical in structure but was reluctant to announce this finding until
she had sufficient evidence. She died of cancer aged 37 years before expressing her
views.
In 1962, when Watson, Crick and Wilkins won the Nobel Prize for
physiology/medicine, Franklin had died. The Nobel Prize only goes to living
216
recipients and can only be shared among three winners. Were she alive, would she
have been included in the prize?
Learning activity 1
The work of scientists
1.Name the three researchers who discovered the structure of DNA and won the
Nobel Prize for physiology/medicine in 1962. (3)
2.Name the researcher that had a degree in Chemistry but did not win the Nobel
Prize. (1) Explain why she did not win it. (1)
3.Where is most of the DNA found in a cell? (2)
4.Mention two other organelles in which DNA is found. (2)
5.What is chromatin? (2)
6.Mention two other genetic discoveries that Francis Crick was involved in. (4)
Total [15]
Where is DNA found?
DNA is found mainly in the nucleus of a cell where it forms an important part of
the chromosomes that make up the chromatin network.
chromatin = chromosomal material made up of DNA, RNA and histone proteins as
found in a non-dividing cell
The DNA molecule is coiled so that these long structures can fit inside the
nucleus. There are nearly two metres of DNA squeezed into each human cell.
You will learn more about the structure of chromosomes in the following unit.
What is extracellular DNA?
Small amounts of DNA are found outside the nucleus in mitochondria in plants and
animals and in chloroplasts in plants. This is called extranuclear DNA.
How is DNA made up?
The shape of DNA is rather like a long, twisted ladder. The two strands twist to form
a stable, 3-dimensional double helix.
DNA double helix
A model of a DNA molecule

217
What units make up DNA?
A DNA molecule is a long chain (polymer) made up of small units (monomers) i.e.
building blocks called nucleotides. Each nucleotide is made up of a:
sugar molecule - deoxyribose (S)
phosphate molecule (P)
nitrogenous base which may be:
adenine (A)
thymine (T)
guanine (G)
cytosine (C)
These four bases are the foundation of the genetic code, instructing cells on how
to synthesise enzymes and other proteins.
As there are four different nitrogenous bases, there are four different nucleotides.
A thymine nucleotide
Before you go any further, make sure you know the names of the four bases.
How is the double helix made up?
The outer two strands of the ladder are formed by a chain of

alternating sugar/phosphate links. The bonds between the sugar and phosphate
molecules are strong.
The rungs of the ladder are formed from pairs of bases linked by weak hydrogen
bonds.
The base pairs are attached to the sugar molecules.
218
How do these four base pairs link up?
The shape and size of the four bases differ so that:
Adenine will only bond with thymine or uracil by means of two hydrogen bonds
eg A=T, A=U.
Cytosine will only bond with guanine by means of three hydrogen bonds eg C ≡ G.
How are the base pairs classified?
There are two groups of nitrogenous bases - purines and pyrimidines.
Purines are made up of two fused rings of nitrogen, carbon and hydrogen atoms.
Examples are guanine and adenine.
Pyrimidines are made up of one ring of similar atoms and are therefore
much smaller than purines. Examples are thymine, cytosine and uracil (see RNA).
As you can see, a base pair is always made up of one purine and one pyrimidine.
Do the bases differ in different organisms?
These four nucleotides are the same in all animals and plants. An adenine
nucleotide of a human is the same as the adenine nucleotide of a frog.
How do organisms differ?
What makes the difference is the sequence in which the nucleotides are strung
together.
For example, the sequence ACCTGA represents different information than the
sequence AGTCCA in the same way that the word ‘post’ has a different meaning
from ‘stop’ or ‘pots’, even though they are made up of the same letters.
The sequence in certain sections of DNA in a human is different from the same
sections in every other human being (except in identical twins).
It is the sequence of the nucleotides (bases) therefore that determines

the genetic code of an organism.
What is the role of DNA?
DNA molecules:
219
carry hereditary information in each cell in the form of genes.
provide a blueprint for an organism’s growth and development by coding for protein
synthesis. (See protein synthesis, page 138)
can replicate, i.e. can make a copy of itself (see page 134) so that a copy of the
genetic information is passed on to each daughter cell formed during cell division.
This ensures that the genetic code is passed on from generation to generation.
What is non-coding DNA?
Less than 2% of a human DNA actually codes for proteins; the rest consists of non-
coding DNA.
Protein-coding regions of a DNA molecule are called exons and they are interrupted
by the non-coding regions called introns.
Complex organisms contain much more of this non-coding DNA than less complex
organisms.
The non-coding regions were thought to be ‘evolutionary junk’ but they are now
known to form functional RNA molecules which have regulatory functions.
Learning activity 2
Structure and importance of DNA
220
Question 1
1.What shape is a DNA molecule? (1)
2.What are the monomers called that make up a DNA molecule? (1)
3.Name the sugar found in DNA. (1)
4.Study the symbolic representation of a DNA molecule and write down the labels 1
to 9. (9)
1. 2.
3. 4.
5. 6.
7. 8.
9.
5.Explain how purines are similar to and differ from pyrimidines. Give examples of
both groups. (8)
[20]
Question 2
1.Why is DNA so important? (2)
2.What is non-coding DNA? (1)
3.What percentage of DNA in a cell is non-coding? (1)
4.What role does this non-coding DNA play? (2)
[6]
Total [26]
Extraction of DNA from organic matter
A variety of methods have been established to isolate DNA molecules from biological
materials and many DNA extraction kits are commercially available. Ideally the
technique should:
release as much DNA as possible
minimize DNA degradation
221
be efficient in terms of cost, time, labour, and supplies.
The extraction method below, using salt and ethanol has proved to:
be simple and time saving
comparatively high yielding.
However, the DNA extracted by manual methods is less pure than DNA isolated by
using commercial kits.
Learning activity 3
Investigation: Extraction of DNA molecules from onion skins
Aim:
To extract DNA from onion skin cells and examine the threads. The chemical
properties of DNA will be used to extract it from onion cells.
Instructions
If equipment is scarce, this investigation can be done as a demonstration but it would

be better to divide the class into groups – the number depending on the number of
learners in the class.
Once the investigation has been completed, each learner is to answer the questions
at the end of the investigation on an A4 sheet which must be handed in.
What is needed by each group?
Large metal pot, mixing bowl, an onion, a sharp knife or a pestle and mortar (if
available), 250 ml cup or beaker, clear dishwashing liquid, salt, coffee filter, funnel,
ethanol, thermometer, thin glass rod.
Procedure
1.Prepare two water baths.
For the hot water bath a large metal pot can be used with a thermometer to ensure
the water stays between 55 0– 600C.
For the cold water bath, a mixing bowl filled with ice and water kept at around 4°C.
2.Prepare onion
Coarsely chop one onion in a pestle and mortar or by hand into a pulpy sludge and
tip it into a 250 ml cup or beaker.
Chopping helps to separate the cells and begins to break down the cell walls.
222
Chopped up onion
3.Make a soap/salt solution
In a 250 ml cup or beaker, dissolve one tablespoon dishwashing liquid and one level
1/4 teaspoon table salt in 100 ml of distilled water. Stir gently to avoid creating foam.
Continue stirring for a few minutes until the salt is dissolved.
The liquid detergent causes the cell membranes to break down so that DNA can be
released.
The salt (NaCl) will enable nucleic acids to precipitate out of an alcohol solution as it
causes the DNA strands to clump together.
4.Pour the solution over the chopped onion
5.Heat in hot bath
Place the mixture in the hot water bath for 10 to 15 minutes (no longer). During this
time, press the chopped onion mixture against the side of the cup/beaker with the
back of the spoon.
The heat treatment softens the phosphorlipids in the cell membranes and denatures
the enzymes which, if present, would cut the DNA into small fragments so that it
could not be extracted in long strands.
6.Cool in cold bath

Cool the mixture in the ice water bath for five minutes. Continue pressing the
chopped onion mixture against the side of the cup with the back of the spoon.
The extracted DNA molecules are fragile and can break apart easily. The cold
conditions cause the chemical reactions to take place more slowly so this slows
down the rate at which the DNA breaks up.
7.Filter the mixture
Filter the mixture through a coffee filter into a clean test tube. This is a slow process.
The filtrate consists of dissolved DNA as well as other biochemicals such as RNA
and proteins.
DNA is a very long molecule but it is small enough to pass through the holes in the
filter paper.
223
8.Add ethanol
Pour the ethanol (alcohol) into a test tube and then chill it by putting it into the cold
water bath. Slowly pour the cold ethanol down the inside of the test tube with the
filtrate to create a 1 cm alcohol layer on top of the filtrate. Try to prevent the ethanol
and filtrate from mixing.
Ethanol dissolves the soluble components of the filtrate forming a solution.
9.Precipitation of DNA
Leave the solution for 2 to 3 minutes without shaking it. DNA and salt,
being insolublein ethanol, clump together, forming a white precipitate at the
interface between the ethanol and the filtrate. This milky white substance is the DNA
of the onion.
precipitate =solid material that comes out of solution due to a chemical or physical
change
DNA precipitating
10.Spooling of DNA
Dip a glass rod into the ethanol layer in the test tube, slowly turning it in one direction
to spool out the onion’s stringy DNA. spool = wrap around
What is the purpose of this experiment?
This simple experiment is an introduction to the procedures of collecting DNA that

are used in molecular biology, e.g. for diagnosing disease or genetic disorders.
Questions
1.Describe the appearance of the DNA you extracted. (2)
2.In your own words summarise the main steps you took to extract DNA molecules
from onions and the importance of each step. (9)
3.Why must the glass rod be rotated in the same direction when spooling DNA? (2)
224
4.Do you think your results would be different if you were to use a fruit or vegetable
other than onions? Explain. (2)
Total [15]
Replication
Replication can be defined as the process of making a new DNA molecule from an
existing DNA molecule that is identical to the original molecule.
This takes place in the nucleus during the interphase (in between cell divisions) in
the cycle of a cell.
Why is replication necessary?
The DNA needs to produce another molecule exactly the same as itself to ensure
that the genetic code is passed on to each new daughter cell formed during cell
division.
How does replication take place?
The process is catalysed by the enzyme DNA polymerase.
The double helix unwinds.
The weak hydrogen bonds holding the base pairs together break, allowing the two
strands to part. Like a zip unzipping.
Each single chain of bases is exposed.
The two strands of DNA
Free nucleotides in the nucleoplasm become attached to their matching, exposed

base partners. Make sure you know what the matching pairs are.
DNA replication itself
The fact that A will only bond with T and C only with G, makes sure that the
sequence of the bases in the daughter DNA is exactly the same as in the parent
DNA. One DNA double helix therefore becomes two identical double helices.
225
Two new strands of DNA are formed; each identical to the original strand.
The two daughter DNA molecules each twist to form a double helix which then winds
itself around the histones (proteins), forming a chromosome. The whole procedure
only takes a couple of seconds.
Learning activity 4
Replication
226
Question 1
In your own words, explain exactly why replication is so important to the

development of an organism.
[3]
Question 2
The following diagram shows a section of a DNA molecule which has just split into
two strands during the process of replication. Draw a new complementary strand
next to it, matching up the base pairs. [5]
Question 3
The following diagram shows a section of a DNA molecule replicating.
DNA strand replicating
1.Name the enzyme that catalyses the process of replication. (2)
2.When does replication take place? (1)
3.What enables the two strands of DNA to separate? (1)
4.Which DNA strand of the diagram is the new strand, the darker one or the lighter
one? (1)
5.Label the four complementary base pairs, 1 to 4. (4)
1 _______________ 2 ______________
3 _______________ 4 ______________
[9]
Total [17]
2. Ribonucleic acid – RNA
RNA is made in the nucleus by DNA. It is involved in protein synthesis.
What is the structure of RNA?
RNA is also a polymer made up of nucleotides, but it differs in structure from DNA
in that:
it consists of a single strand.
227
the strand is much shorter than that of DNA.
the sugar is ribose not deoxyribose.
it has three bases in common with DNA - adenine, cytosine and guanine but a base
called uracil replaces thymine.
What is the function of RNA?
RNA carries instructions from DNA in the nucleus to the ribosomes in the
cytoplasm of a cell where it controls the synthesis of proteins from amino acids.
RNA strand
What are the similarities between DNA and RNA?
1.DNA and RNA are both made up of:
polymers
nucleotides that are made up of a sugar (ribose), phosphate and a nitrogen base
four nitrogenous bases
2.They are both responsible for the synthesis of proteins.
Learning activity 5
Differences between DNA and RNA
Complete the following table that summarises the differences between DNA and
RNA molecules. (10)
DNA RNA
Shape of molecule
Relative length of molecule
Suger present
Bases present
Base pairing
Total [10]
Mitochondrial DNA
As you know, DNA is present in the chromosomes in the nucleus of nearly every cell
of an organism. Small amounts of DNA, however, are also present in the
228
mitochondria in the cytoplasm of cells. This is called mitochondrial DNA
(mtDNA), which:
is a double-stranded, ring-shaped molecule found in all mitochondria.
comes from the egg cell (oocyte) so it is entirely inherited from the mother.
has its own genome of about 16 500 base pairs that code for proteins (enzymes),
tRNA and rRNA. It is therefore much shorter than chromosomal DNA. The genes are
essential for the normal functioning of mitochondria, as they code for the enzymes
that control cellular respiration.
Why is DNA in mitochondria?
Apparently mitochondria were originally separate organisms, i.e. prokaryotes. At

some point they entered a symbiotic relationship with eukaryotic cells through
endosmosis. As a result mitochondria contain their own circular DNA called
mitochondrial DNA or mDNA.
prokaryotes = organisms without a nucleus or any other membrane-bound organelle.

Most are unicellular bacteria
eukaryotes = organisms with a cell nucleus and many membrane-bound organelles,

e.g. animals, plants, fungi and protists.
Tracing genetic links
During fertilisation, only the chromosomes from the sperm enter the egg cell
(ovum); no other organelles.
As a result all the organelles, e.g. mitochondria, in the resultant zygote come from
the cytoplasm of the egg cell, i.e. from the mother.
As mtDNA is passed on from generation to generation, it can be used to establish

a direct maternal genetic line. This means the genes in the mtDNA of the offspring
will be the same as the mother’s, the grandmother’s, the great grandmother’s, etc.
Like all DNA, mtDNA mutates occasionally e.g. substitution can take place where
one nucleotide is replaced by another, resulting in a site known as a marker.
A mtDNA profile of two sets of these markers can be made.
–If the two mtDNA profiles are very similar, the organisms are closely related.
229
–If the two mtDNA profiles show differences, the organisms will have diverged along
different evolutionary pathways.
These markers can be mapped through generations. This enables researchers to

trace lineages through females (matrilineage) and is used to track the ancestry of
human groups/individuals back hundreds of generations.
Note:
‘Mitochondrial Eve’ is named after mitochondria and the biblical Eve. It simply
means that if every person alive today traces their ancestry back through their
mothers and thus their mitochondrial DNA, the Mitochondrial Eve would the first
point on this network where everyone would meet. She probably lived around 200
000 years ago in Africa, supporting the theory that modern humans originated and
migrated out of that continent.
What is mtDNA testing?
If someone is interested to know about his or her family history, a scrape of tissue is
taken from the inside of the cheek and sent to any laboratory of genetic genealogy
for mtDNA testing.
The genetic code is studied at specific locations and the results are compared to the
sequence of mtDNA of other individuals or of the reference sample available in the
laboratory. This reference sample is called the Cambridge Reference Sequence
(CRS) - a source of information of human mitochondrial DNA (mtDNA) commonly
found in people of European descent.
Similar genetic sequences, as shown in the reports of mtDNA testing, indicate a
common female ancestor of the individual being tested.
How can mtDNA profiles be used?
mtDNA profiles can be used to:
reconstruct family maternal-linked relationships.
investigate forensic cases where the chromosomal DNA is degraded.
determine if siblings have the same mother.
Learning activity 6
Mitochondrial DNA and genetic links
Question 1
1.What parts of a cell, other than the nucleus contain DNA? (2)
2.Why is mtDNA inherited only from the mother? (2)
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3.Is your mtDNA the same as your paternal or your maternal grandmother? (1)
[5]
Question 2
A baby named Gladys was kidnapped after the death of her mother. She was raised
by a couple, the Smiths, who claimed she was their biological daughter. The parents
of the deceased mother, the Browns, appeal to a court to try to get custody of
Gladys, who they believe to be their granddaughter.
1.Could mitochondrial DNA testing be useful for this case? In what way? (2)
2.Whose mitochondrial DNA would need to be tested? Why? (2)
3.Assume the relevant people were tested. If the Smiths are telling the truth and
Gladys is their biological daughter, what are the results of the test? If, on the
contrary, the Browns are Gladys’ grandparents what are the results of the test? (2)
[6]
Total [11]
Protein synthesis
231
232
Proteins, which include enzymes, are the workhorses of all living systems; as many
as a hundred million of them may be busy in any cell at any moment.
Are there different types of RNA?
There are different types of RNA made in the nucleus, each of which has a function
in the synthesis of proteins. They are:
messenger RNA (mRNA)
transfer RNA (tRNA) and
ribosomal RNA (rRNA).
A. What happens in the nucleus?
mRNA is formed in the nucleus in the same way as DNA is replicated. The process
is called transcription as the coded message in DNA is carried across (transcribed)
into the new mRNA molecule, which carries it to the ribosome.
Transcription of DNA
Transcription is the process by which DNA makes and codes mRNA.
The process starts when a small piece of DNA, a gene, unwinds.
233
The process is catalysed by the enzyme RNA polymerase which causes the two
strands of DNA to separate by breaking the hydrogen bonds between
complementary DNA nucleotides.
The polymerase attaches to and moves along one of the DNA strands, causing new
nucleotides to pair up with their complementary nucleotides. This DNA strand is
called the template (pattern) as it carries the code.
The nucleotides join up, a sugar-phosphate backbone is added and a new strand of
mRNA is formed.
The sequence of nucleotides is therefore determined by the sequence of the

template DNA nucleotides. In other words the DNA transcribes its genetic code to
the mRNA. The genetic code therefore is simply the sequence of some nucleotides
in a DNA strand.
Note that a uracil base (not a thymine base) will pair with an adenine base.
A completed strand of mRNA breaks away from the DNA. The DNA then re-zips.
The relatively small mRNA moves through the pores of the nuclear membrane and
carries the genetic code to the ribosomes which are the sites of protein synthesis.
What determines which protein is made?
A protein is a long chain (polymer) of small units (monomers) called amino acids.
There are twenty different amino acids that are involved in protein synthesis.
These may combine in various numbers in various sequences to form thousands of
different proteins, - the shortest having 50 amino acids.
Think of how many different words can be formed from the 26 letters of the
alphabet.
The order in which the amino acids are linked determines what kind of protein is
made, e.g. the protein keratin has a different sequence of amino acids from the
protein haemoglobin.
What is the role of mRNA?
The sequence of amino acids is determined by the instructions from the genetic
code in the DNA molecules which is passed on to mRNA.
The genetic code is carried as a sequence of ‘codewords’ which are transcribed to

the mRNA. Each ‘codeword’ is made up of any three bases and is called a codon,
e.g. cytosine – adenine – guanine.
There are 64 different codons and all except three, code for one of the twenty
amino acids used to form proteins. Some amino acids are coded for by more than
234
one codon.
The three codons that do not code for an amino acid are called stop codons. (UGA,
UAA and UAG)
A codon is written, using the first letter of the different bases. For example, the
sequence CCG (cytosine, cytosine, guanine) is the codon for the amino acid glycine
and CAG (cytosine, adenine, guanine) is the codon for valine.
The triplet code of bases is the basis of the genetic code as a gene is made up of a
group of codons that code for the synthesis of one protein.
The order of codons in mRNA will therefore determine the sequence of the amino
acids which will determine which protein is made.
B. What happens at the ribosomes?
The mRNA binds to the ribosome at the start codon (first codon). The codons of the
mRNA act as a template (pattern) that determines the order in which the amino acids
are linked.
What is the role of tRNA?
There are at least 64 different tRNA molecules, made from nucleotides found in the
nucleoplasm of cells.
Each tRNA has three bases at one end called an anti-codon which picks up
a specific amino acid found in the cytoplasm and transfers it to a ribosome.
The most important feature of tRNA is that it can bind to an amino acid at one end
and to mRNA at the other, depositing its amino acid in the correct position to form a
specific protein. See diagram on page 139.
Translation of RNA into proteins
One of the codons, the 'start signal', begins the process of making a protein from
amino acids. Three of these codons act as 'stop signals' that indicate that the
message is over and the protein chain is complete. All the other codons code for
specific amino acids.
The anticodon bases link up to their complementary bases of the codon. This
process is called translation, as the code on the mRNA is translated into a
sequence of amino acids. For example, if the codon on mRNA is GGA, the anti-
codon of the tRNA will be CCU. This enables amino acids to link up in the correct
sequence.
You do understand why, don’t you?

235
The tRNA molecule is released to carry more of its specific amino acid to the
ribosome.
Catalysed by enzymes, the amino acids link together with peptide bonds to form a
polypeptide chain.
The polypeptide chains link together to form the final functional protein.
To sum up:
Translation is the process by which a specific protein is formed from a chain of

amino acids due to the sequence of codons in the mRNA, which, in turn, was coded
by the DNA.
What is the role of rRNA?
rRNA is the most common form of RNA in the cell and it, together with proteins,
makes up the ribosomes.
The rRNA moves from codon to codon along the mRNA, reading the code. rRNA
therefore plays an important role in controlling the process of protein synthesis.
This is all a bit confusing! Go over the following simple summary and diagrams
very carefully. They should help you to understand the process.
Did you know?
Less than 2% of a human DNA actually codes for proteins; the rest consists of non-
coding DNA which is not translated into useful proteins. Scientists believe however,
that this non-coding DNA cannot be ‘junk’ and have no purpose as, if this were the
case, the evolutionary process would have got rid of it.
How do antibiotics interfere with protein synthesis?
Pharmacological drugs such as antibiotics are produced to counteract bacterial

infections.
They do this by interacting with the bacterial ribosomes and inhibiting their
function of protein synthesis.
The ribosomes of bacteria (prokaryotes) and eukaryotes are different enough that
antibiotics can specifically target those of the bacteria and not those of the host.
Proteins are essential for the production and growth of new cells so, if bacteria are
prohibited from making proteins, they will not be able to make new cells to spread
the infection.
There are many different antibiotics that inhibit protein synthesis by interacting with
the bacterial ribosomes in different ways, eg:
236
the tetracyclines prevent the attachment of tRNAs carrying amino acids
chloramphenicol, prevents the formation of peptide bonds.
By targeting different stages of the mRNA translation, antibiotics can be changed if

resistance develops.
Learning activity 7
Protein synthesis
Read the text and very carefully and neatly fill in the relevant labels on the
diagrams. Enjoy thinking!
1.The mRNA, with its codons, moves through the pores of the nuclear membrane
into the cytoplasm where it binds with a ribosome.
2.The tRNA with its anti-codons links up with a specific amino acid in the
cytoplasm.
3.The tRNA brings its amino acid to the ribosome where the anti-codon links up
with its complementary codon.
4.The amino acid is released and links up with the adjacent amino acid by means of
a peptide bond. The tRNA molecule is also released. The rRNAmoves along the
mRNA strand, reading the code.
5.When the end is reached a completed polypeptide chain has been formed, built
according to the code of the mRNA, which was originally copied from the DNA code
in the nucleus.
Total [16]
It is amazing that the genetic code evolved just once and that the same code
applies to ALL living organisms. These processes have been going on non-stop
since life began, 3.5 bya.
Note:
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If a chain of amino acids is made up of less than 50 amino acids, it is called
a polypeptide. More than 50 amino acids is called a protein.
To sum up:
Protein synthesis involves two separate procedures:
In the nucleus, the transcription of the DNA code onto the mRNA molecule.
In the ribosomes, the translation of this message into the formation of polypeptides
and proteins.
Learning activity 8
General protein synthesis questions
Question 1
1.Where in the cell does protein synthesis take place? (2)
2.What are the building blocks of proteins called and how many different types of
these units are there? (2)
3.What is responsible for coding the correct instructions regarding the sequence in
which the amino acids are arranged in a protein? (2)
4.DNA is found in the nucleus, but proteins are made outside the nucleus. What is
used to carry information from the nucleus to the sites of protein synthesis? (2)
5.Which proteins are responsible for controlling all the metabolic reactions taking
place in a cell? (2)
6.Explain why the strand of amino acids in Learning activity 7 is labelled a

polypeptide chain and not a protein. (2)
[12]
Question 2
Answer the questions in the spaces provided.
1.What are codons and where are they found? (3)
2.Transcribe the following genetic code of DNA into codons:

TAC/GGT/TTG/TAT/GCA/CAG. (3)
3.What are anticodons and where are they found? (3)
4.Write down the anticodons for the codons in number 2. (3)
[12]
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Total [24]
Genetic aberrations
Genetic aberrations are caused by mutations.
A mutation is any alteration in the genetic makeup (genetic code) of an organism.
Factors that lead to genetic changes (changes in the sequence of nucleotides)

during a lifetime may be caused by:
1.One or more nucleotides being damaged or lost by chance:
crossing over of paternal and maternal chromosomes in meiosis
replication of DNA
transcription of DNA to RNA.
2.Breakdown of DNA by mutagens, e.g.:
environmental factors such as sunlight, radiation and smoking
mutagenic chemicals (e.g. formaldehyde, benzene, carbon tetrachloride)
viruses and micro-organisms.
mutagen = physical or chemical agents that induce and speed up mutations in DNA
Gene mutations
Gene mutations are small, localised changes in the structure of DNA strands.
Changes that involve a single nucleotide are called point mutations. They may
occur by:
substitution – where one nucleotide is exchanged for another.
insertions – where one or more extra nucleotides are added to the DNA molecule.
deletions – where one or more nucleotides are removed from the DNA molecule.
Examples of point mutations
When the sequence of nucleotides is altered, individual codons are affected, altering
the mRNA transcribed from the mutated DNA. This causes the absence of, or
incorrect form of the protein for which that gene codes.
Application of DNA technology
One of the ways that DNA technology can be applied is in DNA profiling or
fingerprinting.
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DNA profiling/fingerprinting
Each person has unique DNA (except for identical twins), despite the fact that 99.9%
of human DNA is identical. The differences occur in the highly variable, non-
coding part of DNA.
DNA profiling involves the extracting and identifying the highly variable regions of a
person’s DNA that contain repeating sequences of base-pairs called STRs (short
tandem repeats), e.g. CAGACAGACAGA is a repeat of CAGA three times.
At the same point in the DNA of different people, the number of repeated sequences
of base pairs varies considerably, so distinguishing one DNA profile from another.
From 13 to 20 different sites on DNA molecules are investigated; enough to show

that an individual’s profile is unique.
Scientists can use these repeated sequences that vary to generate a DNA profile of
an individual, using samples from blood, bone, hair and other body tissues and
products.
DNA profile = an individual’s unique DNA fragments, separated by electrophoresis
How is a DNA profile made?
The cells are treated with chemicals to extract the DNA.
Restriction enzymes are used to cut at the beginning and end of each repeated
sequence, resulting in fragments of different lengths.
Through a complicated process known as Polymerase Chain Reaction, or PCR,

large numbers of these fragments are made to provide a substantial amount of DNA
to work with.
Polymerase Chain Reaction, or PCR = a laboratory technique used to make multiple

copies of a segment of DNA
The DNA fragments that result are then separated and detected, using different
techniques such as electrophoresis.
gel electrophoresis = a method to separate large molecules mainly on the basis of
size and electrical charge
In this way a pattern is obtained that reflects different numbers of base pair repeats
in different individuals; the length of a particular DNA fragment depends on the
number of repeats present. These separated DNA fragments are represented as
dark bands on a piece of film. This is a DNA fingerprint.
Each of our cells carries an identical set of this unique DNA that differs from that of
any other person (except in identical twins).
240
If two genetic profiles show identical banding patterns, it is virtually certain that they
come from the same person.
In related people, some parts may be similar, but no-one else will have exactly the
same sequences in every part of their DNA. The following picture shows a set of a
family’s DNA fingerprints.
Can you see which child has genes (STRs) from which parent?
DNA fingerprints
Note:
DNA is a non-reactive and chemically inert molecule which is why it can be

recovered from patches of long-dried blood or semen in murder investigations and
even extracted from bones of ancient Neanderthals.
What are the uses of DNA profiling?
1. Forensics
forensics = the use of different scientific technologies to investigate a crime

Identifying differences in the DNA of individuals is very useful in forensic
investigations. Because each individual has its own unique genetic sequence, DNA
can provide a means of identification accurate enough to be used in the courtroom.
Traces of DNA left at a crime scene can often prove to be crucial evidence, eg if
stains of blood, skin or semen left on the victim can be matched to DNA fingerprints
of the suspect, the criminal has been found.
In addition, this technology has reversed convictions and set innocent people free.
Note:
Where there is no suspect for a particular crime, DNA samples collected at the crime
scene may be compared with DNA profiles stored on a National DNA Database. This
is a resource which contains DNA profiles of people suspected and convicted of
crimes. If a match is made between a sample and a stored profile, the criminal can
be identified.
2. Diagnosing inherited disorders
DNA profiling provides medical professionals with information needed to determine

hereditary diseases. This enables parents to make decisions concerning affected
pregnancies and gives them a chance to prepare for proper treatment of an affected
child.
3. Identifying casualties
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If the army kept a set of DNA fingerprints of all soldiers, they could be used to
identify unrecognizable casualties.
4. Paternity testing
Another important use of DNA fingerprinting in the court system is to establish

paternity in custody and child support disputes or to determine parents if babies
have been switched in a maternity home.
5. Fight illegal trading
The origin of timber, etc. may be identified to fight illegal trading.
What are the disadvantages of DNA profiling?
1. Violation of privacy
Many people believe that the use of DNA profiling to store identifiable information
about people is a violation of privacy. This could be harmful, e.g. the information
regarding genetic traits could lead to health insurers denying coverage or claims.
2. Issues on accuracy
The accuracy and efficiency of DNA fingerprinting depends on the competency of

equipment, laboratory personnel and experience. Possible errors in the procedures
inside the laboratory can lead to incorrect information.
3. Manipulation
Tampering, irresponsible handling and manipulation of data in genetic profiling, could

lead to false information.
Learning activity 9
DNA profiling and forensics
Question 1
1.How many different sites on the non-coding sections of a DNA molecule are
usually analysed in constructing a DNA profile? (1)
2.What makes these sites suitable for DNA profiling? (2)
3.What distinguishes one STR from another? (2)
[5]
Question 2
The DNA profiles below are a hypothetical example of a forensic result where the
victim, Z, was raped and murdered. There were three suspects in this case and
blood samples were taken from each so that fingerprints could be made of their
242
DNA. A semen sample was taken from the body of the victim and used as evidence
– Y on the X-ray film.
1.Which of the three suspects was probably the killer? (2)
2.Explain how you came to this conclusion. (2)
3.Explain why a sample was also taken from the victim and analysed. (2)
4.Explain the term forensic. (2)
[8]
Total [15]
Short questions
1. Multiple choice
answer below.
1 2 3 4 5 6 7 8 9 10
1.What is the function of DNA in the cell?
(a) Releasing energy into a cell.
(b) Controlling the functioning of a cell.
(c) Digesting food.
(d) Initiating cell division.
2.Which compounds from the following list form a nucleotide of DNA? 1 - phosphate,
2 - nitrogenous base, 3 - lipid, 4 - glucose, 5 - ribose, 6 - deoxyribose
(a) 1, 2 and 3; (b) 1, 2 and 5; (c) 2, 3 and 6;
(d) 1, 2 and 6.
3.When a DNA molecule makes an exact copy of itself it is called: (a) transcription;
(b) meiosis; (c) translation; (d) replication.
243
4.During replication of DNA, thymine always pairs with: (a) uracil; (b) guanine; (c)
cytosine; (d) adenine.
5.DNA and RNA molecules are similar in that they both contain: (a) ribose; (b)
deoxyribose; (c) adenine; (d) thymine.
6.If the order of the bases in a strand of DNA is: adenine - guanine - cytosine –
thymine, the order of bases in the mRNA transcribed from it would be:
(a) thymine - cytosine - guanine - adenine
(b) uracil - guanine - cytosine - adenine
(c) uracil - cytosine - guanine - adenine
(d) thymine - cytosine - guanine - uracil.
7.During transcription of mRNA, thymine always pairs with: (a) uracil; (b) guanine; (c)
cytosine; (d) adenine.
8.Which statement is incorrect with regard to RNA?

(a) The anticodons of the mRNA act as templates for the building of a specific
protein.
(b) The tRNA carries the amino acid to the ribosomes and places it in the right
sequence.
(c) A ribosome moves along the mRNA, interpreting the code. (d) Codons and
anticodons of RNA are both made up of base triplets.
9.The RNA molecule that can join up with codons as well as amino acids is: (a)
mRNA; (b) tRNA; (c) rRNA; (d) none of the above.
10.mtDNA testing is important as it can be used to… (a) reconstruct family maternal-
linked relationships. (b) investigate forensic cases where the chromosomal DNA is
degraded. (c) determine if siblings have the same mother. (d) all of the above.
[10]
2. Terms
Give the correct term for each of the following.
1.The monomers of nucleic acids.
2.The monomers of proteins.
3.The shape of a DNA molecule.
4.The process by which DNA copies itself.
5.The synthesis of mRNA from a segment of DNA.
6.The nitrogenous base which is found in RNA in the place of thymine.
7.Each ‘codeword’ on mRNA that corresponds to a single amino acid.

244
8.Three bases found on the loop of tRNA which are complementary to those on
mRNA.
9.A long chain made up of small units.
10.The proteins in a chromosome.
11.Agents that induce and speed up mutations in DNA.
12.The group of nitrogen bases made up of one ring of nitrogen, hydrogen and
carbon atoms.
[12]
10
11
12
3. Mix and match questions
Choose a description from Column B to match each word in Column A and write the
correct letter next to the appropriate number.
1.mRNA A.The process of copying a DNA molecule
2.tRNA B.Carries codes for specific amino acids
245
3.DNA and C.The monomers of proteins
proteins
4.junk DNA D.Makes up chromatin network
5.replication E.Takes place at the ribosomes
6.transcription F.Formation of mRNA
7.translation G.The monomers of nucleic acids
8.nucleotides H.Carries amino acids to the ribosomes
9.amino acids I.The process whereby amino acids link up to form

proteins
10.protein J.Non-coding DNA

synthesis

word word
1.DNA and RNA nucleotides are made up of a sugar,

a phosphate group and a nitrogenous base.
2.Proteins are synthesised from amino acids in the

mitochondria of cells.
3.Replication of DNA takes place during meiosis.
4.RNA differs from DNA in that uracil replaces the

base adenine.
5.All enzymes that control our metabolic reactions

are proteins.
6.Translation is the process by which DNA makes

mRNA.
7.Transcription and translation are both processes
246
necessary for protein synthesis.
8.Amino acids are linked together by hydrogen

bonds.
9.mRNA reads the genetic code at the ribosomes.
10.Franklin, Watson and Crick won the Nobel Prize

for physiology/medicine in 1962.
11.DNA is found in the nucleus and in the

mitochondria of cells.
12.Thymine, cytosine and uracil are pyramidines that

are made up of two rings of atoms.
13.Changes in a single nucleotide are called point

mutations and are caused by mutagens and chance.
[21]
Total [53]
Chromosomes and meiosis
Chromosomes
Chromosomes are long, thread-like structures that form part of the chromatin
network in the nuclei of cells.
They are made up of a strand of DNA wound around proteins called histones.
A section of a chromosome
Chromosomes were discovered by chance in 1888. They absorb dye very easily
which is why they were called chromosomes – coloured bodies. This makes them
visible under a microscope but they can only be seen as individual threads when a
cell is dividing.
Electromicrograph of human chromosomes
In somatic (body) cells of diploid organisms:
the number of chromosomes in each cell is the same.
247
the chromosomes are made up of two sets; one chromosome of each pair comes
from the mother (maternal chromosome) and one comes from the father (paternal
chromosome). They are therefore called diploid cells (di – two) or 2n for short.
For each paternal chromosome there is a matching maternal chromosome forming

a homologous pair. The chromosomes forming a pair are the same size and shape
and have the same genes in the same place, but the alleles (see unit 3.3) for each
trait may not be the same.
The DNA of each chromosome replicates to form two identical

threads or chromatids joined by a centromere. This takes place in
the interphase of a cell cycle, i.e. between cell divisions. These threads only
become visible when they shorten and thicken as a cell divides.
Replication of DNA is very important to ensure that, as a cell divides, each daughter
cell receives a full complement of all the genetic material.
Homologous chromosomes
Learning activity 1
Chromosomes
Question 1
1.Name the mass of interwoven threads found in the nucleus in the interphase. (2)
2.At which stage of the cell cycle does replication take place? (1)
3.Why is replication so important? (3)
4.What is another name for a body cell? (1)
5.Each body cell has two sets of chromosomes. What name is used to describe this
and how is it abbreviated? (2)
6.What do we call chromosomes inherited from the father? (1)
[10]
Question 2
Fill in the labels on the diagram below of chromosomes that have replicated.
[4]
248
Total [14]
What is meant by chromosome number?
Each species has a specific number of chromosomes in its somatic cells. Some
organisms have identical chromosome numbers but these need not be related. It is
the similarities in the DNA of the chromosomes that show relationships, not their
number.
Organism Chromosome number
mosquito 6
cabbage 18
sunflower 34
cat 38
human 46
potato 48
chimpanzee 48
dog 78
goldfish 94
Meiosis
In Grade 10 you learnt about how cells divide by mitosis to enable organisms to
grow and repair damaged tissue.
What is meiosis?
Meiosis is cell division that takes place in the reproductive organs of both plants
and animals to produce gametes (sex cells) in animals and spores in plants.
In meiosis the number of chromosomes is reduced from two sets (2n) in the parent
cell to one set (n) in each of the daughter cells formed, i.e. the number of
chromosomes is halved.
The gametes/spores formed are called haploid as they only have one set of
chromosomes, i.e. one chromosome from each homologous pair.
In sexual reproduction a male haploid gamete fuses with a female haploid gamete
during fertilisation to form a diploid zygote.
249
Where does meiosis take place?
In animals meiosis takes place in the reproductive organs, the testis and ovaries.
The formation of sperm cells in the testis is called spermatogenesis.
The formation of egg cells or ova in the ovaries is called oogenesis.
In plants meiosis takes place in the formation of spores in sporangia. In seed-

bearing plants:
microsporangia are the pollen sacs in the male anthers
megasporangia are the ovules in the female ovaries.
Learning activity 2
Chromosome number and cell division
1.On the diagram of a life cycle below, fill in the relevant processes, 1 to 3, and then
an n or a 2n in each of the circles to indicate the number of sets of chromosomes.
Outline of life cycle of an animal

250
[7]
2.Study the diagram in the adjacent column and in the spaces below, fill in the:
chromosome numbers, 1 to 6
processes, 7 to 9
names of the different cells, 10 to 12. [12]
Note that the chromosome number in humans is 46.
Chromosome numbers
1. _________2. _________3. _________
4. _________5. _________6. _________
Cell processes
7. ___________________________________
8. ___________________________________
9. ___________________________________
Names of cells
10. ___________________________________
11. ___________________________________
12. ___________________________________
Total [19]
Correct any mistakes you made and learn from your mistakes. This diagram
shows you just how important meiosis is.
The process of meiosis
The DNA of the parent cells is replicated in interphase preceding both mitosis and
meiosis. However, in meiosis, replication is followed by two divisions.
Meiosis 1 is a reduction division which results in two cells being formed each
with half the number of chromosomes of the parent cell, i.e. the haploid
(n) number.
Meiosis 2 is a copying division which involves the two haploid cells formed, each
dividing again by mitosis to form 4 haploid cells.
251
Note that in the first diagram in Learning activity 2, not all four gametes have
been drawn – only two.
Meiosis 1 – a reduction division
Early prophase 1
As in mitosis, the chromosomes become short and fat and are visible as two
chromatids joined by a centromere.
From here on the behaviour of the chromosomes in meiosis 1 and in mitosis differs.
Late prophase 1
The chromosomes of homologous pairs lie along side one another, forming
a bivalent.
The centrioles move to opposite poles.
A spindle, made up of protein threads, develops across the cell from the two
centrioles.
It is at this stage that crossing over takes place.
For an explanation of this see page 154.
Metaphase 1
The bivalents (not the chromosomes) move to the middle of the cell and line up on
the equator.
The centromeres become attached to the spindle threads.
Anaphase 1
The centromeres do not split. The bivalents separate and the chromosomes (not the
chromatids) are pulled away from each other by the contracting spindle threads. The
chromosomes move to opposite poles of the cell.
Telophase 1
The cytoplasm then divides (cytokinesis) to form two haploid cells, i.e. both the new
cells only have one of each homologous pair of chromosomes.
252
Meiosis 2 – a copying division
The two chromatids making up each chromosome need to separate. Each of the
haploid cells will therefore divide again by mitosis.
Learning activity 3
Meiosis 2 – a copying division
Read through the text carefully and fill in the labels in each of the following diagrams.
Late prophase 2
Each chromosome is made up of two chromatids joined by a centromere.
A spindle, made up of protein fibres develops.

The nuclear membrane disappears.
Metaphase 2
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The chromosomes move to the middle of the cell where they line up at the equator.
The centromeres become linked to the spindle threads.
Note:
The markings on the chromosomes show how they separate during mitosis 2.
Anaphase 2
The centromeres spilt, allowing each chromosome to separate into two chromatids.
Spindle threads contract and pull the chromatids apart. The chromatids, which are
now called daughter chromosomes, move to opposite ends (poles) of the cell.
Telophase 2
Daughter chromosomes group together at the poles. A new nuclear membrane starts
to form around each set of daughter chromosomes.
Cytokinesis
The cytoplasm starts to divide forming two new daughter cells, each with the haploid
number of chromosomes. This process is called cytokinesis. A new nucleolus forms.
At the end of meiosis four new, non-identical, haploid cells are formed from one
parent cell, each with half the original number of chromosomes. The gametes
are not identical to the parent cell.
A summary of the movement of chromosomes during meiosis
Note:
2 chromatids make up a chromosome.
2 chromosomes make up a homologous pair.
A pair of homologous chromosomes in close contact with each other make up a

bivalent.
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Learning activity 4
Meiosis
Question 1
The micrograph below shows cells in various stages of meiosis. On the diagram,
label as many different stages of meiosis as you can see. [5]
Question 2
1.In humans where does meiosis occur? (2+2)
2.Explain why it is necessary for gametes to be formed by meiosis. (2)
[6]
Total [11]
Crossing over
Crossing over is the mutual exchange of pieces of chromosome so that whole

groups of genes are swapped between maternal and paternal chromosomes. This
takes place in late prophase of meiosis 1.
The replicated homologous pairs of chromosomes come together in a process

called synapsis to form bivalents. They swap pieces of their inner chromatids by
breaking and reforming their DNA while they are paired up.
The points of crossing over where the chromatids break are called chiasmata.
singular: chiasma
In this way some genes from a maternal chromatid change place with some genes
from a paternal chromatid, forming a recombinant chromatid. The outer,
unchanged chromatids are called parentals.
The process of crossing over
Why is crossing over important?
The exchange of genetic material produces chromatids with a unique combination

of genes. This increases variation among the daughter cells as there will be new
combinations of genetic material. This is why the offspring do not look the same
(except for identical twins) or like their parents.
During this exchange process, mistakes may occur which lead to mutations. Most
mutations are harmful but occasionally they may be beneficial. In this way new
255
genes may be introduced into the genetic make-up of a species which can influence
evolution.
Why is meiosis important?
1.Gametes are formed by the process of meiosis.
2.During meiosis the number of chromosomes is halved so that the chromosome

number is kept constant from generation to generation.
3.Meiosis results in genetic variation through:
crossing over
random arrangement of chromosomes at the equator of the cell during metaphase.
Learning activity 5
Meiosis and crossing over
256
Question 1
Study the three diagrams below and answer the questions that follow.
1.What do we call the pair of homologous chromosomes, A B? (1)
2.What process is taking place in diagram C? (1)
3.Label the structure F. (1)
4.During which type of cell division, mitosis or meiosis, does this process take place?
(1)
5.During which phase of this cell division does it occur? (1)
6.Name the chromatids, D and E. (2)
7.How does the process taking place in the diagram benefit an organism? (2)
[9]
Question 2
Choose the word from Column B that best describes the statement in Column A and
write the letter in the space provided. (12)
Column A Column B
1.Contraction of spindle threads A.crossing over
2.23 pairs of chromosomes B.meiosis 1
3.23 chromosomes C.telophase 2
4.Reduction division D.early prophase
5.Cytoplasm dividing E.meiosis 2
6.Chromosomes become visible F.interphase
7.Copying division G.late prophase
8.Formation of bivalents H.somatic cells
9.Chromosomes form chromatin network I.anaphase
10.Pairs of chromosomes at the cell equator J.cytokinesis
11.Exchange of pieces of chromatids K.metaphase 1
12.Replication of DNA L.gametes
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1 2 3 4 5 6 7 8 9 10 11 12
[12]
Total [21]
What are the similarities between mitosis and meiosis?
Both are types of cell division.
The DNA of the parent cells is replicated in interphase before cell division starts.
In early prophase the chromosomes become short and fat and are visible as two
chromatids joined by a centromere.
As you study this table, try to imagine both processes taking place.
What are the differences between mitosis and meiosis?
Process Mitosis Meiosis
Where the It takes place in plants and In plants it takes place in

process animals in the development of the sporangia of the sporophyte
occurs a zygote to an embryo and generation, in the formation
then the cells continue to divide of spores.
by mitosis to form a mature
In animals it takes place in the
organism.
reproductive organs,
In plants it takes place in the testis and ovaries, in the
the meristemmatic tissue to formation of gametes.
bring about growth, e.g. in
buds, root tips and in the
cambium.
In animals it takes place in the

growing regions of bones, in the
skin, in areas that are
damaged.
The The purpose of mitosis is to The purpose of meiosis is to halve

purpose of keep the number of the number of chromosomes, i.e.
the chromosomes in the daughter the diploid number of
process cells the same as the number chromosomes in the parent cells
of chromosomes in the is reduced to the haploid
258
parent cell. number in the gametes or spores
formed. This is to prevent
This cell division is involved in:
chromosome numbers
development of an adult doubling after fertilisation in
organism from a single zygote. sexual reproduction.
growth and repair of tissues.
regeneration of body parts.
asexual reproduction.
Differences Involves one cell division. In prophase 1: bivalents formed

in the and crossing over occurs.
In prophase: no bivalents
process
formed and no crossing over. In metaphase the centromeres do
not split.
In metaphase: the centromeres
split. In anaphase the chromosomes of
each homologous pair move to
In anaphase the chromatids of
opposite poles of the cell.
each chromosome move to
opposite poles of the cell. Four daughter cells are formed
each with half the number of
Two daughter cells are formed
chromosomes as the parent cell,
with the same number of
i.e. haploid.
chromosomes as the parent
cell, i.e. usually diploid. Gametes are formed which are
genetically different to each other
Somatic cells are formed
and to the parent cell.
which are similar genetically to
the parent cell. • Involves two
cell divisions.
Abnormal meiosis
Abnormal meiosis results in chromosome abnormalities and it can take place in

several different ways. Chromosome non-disjunction 0ccurs when chromosomes
fail to separate correctly during meiosis.
If this occurs in the sex chromosomes (X and Y), fertilization involving one of these
abnormal gametes will result in a zygote with either an extra or a missing
chromosome – a condition known as aneuploidy. Affected individuals have physical
and mental characteristics called syndromes.
The following are two examples of aneuploidy. In both cases the cause of the event
is chromosome non-disjunction and the effects are the various
259
syndromes. Remember that the cause is the producer of an effect, while an effect is
produced by a cause.
Two other words to distinguish between are:
Diagnosis is identifying the nature of an event (e.g. an illness),

whereas prognosis is predicting how the event (as in illness) will develop.
Klinefelter’s syndrome
Klinefelter’s syndrome is an example of aneuploidy. It occurs in males when a boy is

born with an extra copy of the X chromosome (XXY). This occurs when the sex
chromosomes in the egg (or very rarely the sperm) split unevenly.
Many men with Klinefelter’s syndrome do not have obvious symptoms and in others
their male sexual development and fertility may be interfered with, e.g. they may
have:
sparse body hair
enlarged breasts
small testicles and penis
not very deep voices.
They usually cannot father children.
Down syndrome
Down syndrome is another example of aneuploidy that occurs in children who are
born with an extra (third) copy of chromosome number 21 in their cells, i.e.
(2n+1) – a condition known as trisomy.
Did you know?
260
Down syndrome is named after John Langdon Down, a British doctor who first
described the condition in 1887. It was not until 1959 that an extra chromosome was
diagnosed as the cause.
How does this come about?
During oogenesis (meiosis in the production of an egg), the two number 21

chromosomes do not separate properly during anaphase 1; both go into one
daughter cell instead of one into each of the two daughter cells formed. It is
apparently rare for males to be the cause of Down syndrome.
This results in an egg with two number 21 chromosomes instead of one.
If this egg is fertilized, the zygote will have three number 21 chromosomes (one
from the father and two from the mother) and a total of 47 chromosomes in each
cell instead of 46.
As the new embryo develops by mitosis, all the cells will have 47 chromosomes.
What are Down syndrome characteristics?
Children have varying degrees of mental retardation. The severity of symptoms

differs widely from person to person.
They have distinctive flattened facial features with slightly slanting eyes due to
folds of skin at the corner of the eyes.
Other physical features include short stubby fingers and toes with the big toes widely
spaced from the second toe, a largish head and ears that may develop differently.
These problems are often accompanied by heart defects and other health
problems.
Despite their many problems, Down syndrome sufferers tend to have a happy,
loving nature.
Although some of the health problems caused by Down syndrome, such as heart
defects, may be treated through surgery and medication, there is no cure.
Boy with Down syndrome
How common is Down syndrome?
Down syndrome is a relatively common birth defect, affecting about 1 in 900 births.
The chances of having a baby with Down syndrome increase with the age of the
mother; a 35 year old woman has a 1 in 350 chance, whereas a woman of 45 has a
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1 in 30 chance. With age the chromosomes seem to have more difficulty in
separating. This is known as the maternal age effect.
Do children with genetic abnormalities have problems?
Children with Down and other syndromes tend to grow and develop more slowly than
other children. In many countries, since the early 1960s, Down syndrome children
attend mainstream schools and not special institutions. Some may need special
classes to help them in areas where they have more trouble learning.
Despite this change in attitude towards educating people with genetic abnormalities,
they still need support. Because they are different from other people, they often
encounter patronising attitudes and discrimination in the wider community. It is
important, therefore, that parents work with teachers and others to come up with a
plan to help each child to learn and to live a normal, integrated, carefree life.
What about aborting the foetus?
A new test, taken early in pregnancy, combines a blood test with an ultrasound
examination. This can pinpoint many foetuses with Down syndrome 11 weeks after
conception and it therefore allows expectant women more time to decide whether to
undergo the risky follow-up testing needed to confirm the diagnosis or to abort the
foetus. In the follow-up process, the foetal cells can be extracted from the amniotic
fluid by amniocentesis. The karyotype of these cells can then be determined.
amniocentesis = a process whereby a small sample of fluid is removed from the

amniotic cavity in the uterus.
Note:
In the United States 91 to 93% of pregnancies with a diagnosis of Down syndrome

are terminated. Physicians and ethicists are concerned about the ethical
ramifications of this.
Learning activity 6
A class debate on aborting foetuses with Down syndrome
Select two groups of about three speakers. Draw out of a hat which group is to
support abortion and which group to oppose it. Each group is given time to decide on
its approach to the debate regarding the:
ethical concerns
physical dangers
After the debate, members of the class vote for or against abortion.
What is a karyotype?
262
A set of chromosomes in a cell is called a karyotype. It shows the number, size and
shape of the chromosomes during metaphase of mitosis.
Something extra
Karyotypes are prepared from the nuclei of cultured white blood cells. After these
cells are stimulated to divide and grow in a culture medium for several days, they are
treated with a drug that arrests mitosis in metaphase - a phase when the
chromosomes are easily identified. The chromosomes are dyed and then
photographed. The photographs are entered into a computer that arranges them in
homologous pairs. The structure and number of chromosomes can then be studied.
In the human karyotype that follows, non-sex chromosomes, autosomes, of a

similar size are grouped together and placed in groups A to G according to their
length. The sex chromosomes, gonosomes (X – female; Y – male) are placed
separately.
Can you see the homologous pairs in the karyotype below?
A human karyotype
Karyotypes are useful as they can show:
whether a cell comes from a male or a female
abnormal chromosomes.
Learning Activity 7
Chromosome mutations
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Question 1
The diagrams below show the chromosomes of two different children.
1.Study the diagrams and give two differences between child A and child B. (4)
2.Which child, A or B, has an abnormal set of chromosomes? (1)
3.This genetic disorder is called Down syndrome and it can be detected in an unborn
baby by amniocentesis. What does this process involve? (3)
4.In the above case would you advise the mother to abort the baby or go to full term?
Give a reason for your answer. (3)
5.What difference would you see if the chromosomes had been taken from a sex
cell? (2)
6.How can you tell that the somatic cell these chromosomes came from was not a
mature red blood cell? (2)
[15]
Question 2
1.What is meant by trisomy? (2)
a.The table below shows the chances of having a Down syndrome baby for women
of different ages.
Age Chance
25 1 in 1 500
30 1 in 800
35 1 in 300
40 1 in 100
45 1 in 30
2.How does this support the theory that Down syndrome is caused by a defect in
egg/ovum formation? (3)
3.Which chromosome pair is represented by 3 chromosomes instead of 2? (1)
4.During which phase of meiosis does this chromosome mutation take place? (1)
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5.State how many chromosomes would be present in the somatic cells of an
individual with Down syndrome. (1)
6.Of all the altered phenotypic characteristics, which two do you consider to be the
most common and noticeable in a Down syndrome child? (2)
[10]
Total [25]
Learning activity 8
Short questions
1. Mix and match
1. interphase A. Synapsis
2. crossing over B. Copying division
3. bivalent C. Replication of DNA
4. human gametes D. 46 chromosomes
5. meiosis 1 E. Division of cytoplasm
6. meiosis 2 F. Made up of DNA and proteins
7. karyotype G. Exchange of genes
8. chromosome H. The complete set of chromosomes in a cell
9. human zygote I. 23 chromosomes
10. cytokinesis J. Reduction division
[10]
In each case, write down whether the statement is true or false, and if false, write
down the incorrect and correct words.

word word
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1.A centriole attaches two chromatids together.
2.Meiotic division takes place in two stages, a

reduction division and a copying division.
3.In an animal cell a spindle is formed between two

centromeres.
4.Crossing over involves the exchange of segments

of outer chromatids in a bivalent.
5.A human somatic cell contains 23 chromosomes.
6.Mitosis and meiosis are both different types of

nuclear cell division.
7.Synapsis takes place in late prophase 1 of

meiosis.
8.In meiosis four daughter cells are formed, all

identical to their parent cell.
9.Down syndrome and Klinefelter’s syndrome are

both examples of polyploidy.
[15]
3. Terms
1.The period between divisions during which the cell performs its normal 1
functions.
2.The name of the genetic material in a cell during the phase mentioned 2
above.
3.The phase in meiosis where synapsis occurs. 3
4.The exchange of chromatid segments of a bivalent. 4
5.The process which reduces the diploid number of chromosomes to the 5

haploid number.
6.The organelle which gives rise to the spindle in a dividing animal cell. 6
266
7.The phase in the process of meiosis where the bivalents arrange 7
themselves in the equator of the spindle.
8.The process in which the cytoplasm divides after nuclear division in an 8

animal cell.
9.A cell that only has one set of chromosomes. 9
10.Physical and mental characteristics of a disease. 10
[10]
statement.
Aif only item 1 relates to the statement
Bif only item 2 relates to the statement
Cif both items 1 and 2 relate to the statement
Dif neither item 1 or 2 relate to the statement
1. 1. mitosis reduces the diploid number of

2. meiosis chromosomes to the haploid
2. 1. mitosis takes place in the gonads

2. meiosis
3. 1. chromatin network visible in interphase

2. chromosomes
4. 1. prophase replication of DNA takes place

2. interphase
5. 1. metaphase chromosomes lengthen and become

2. anaphase chromatin network
6. 1. plant cell cytokinesis takes place

2. animal cell
7. 1. plants mitosis and meiosis occur
267
2. animals
8. 1. prophase of meiosis 1 crossing over takes place

2. anaphase of meiosis 1
9. 1. anaphase of meiosis 1 chromosomes are pulled to opposite

2. anaphase of meiosis 2 poles of the cell
10. 1. crossing over brings about variation of the offspring

2. independent assortment of
chromosomes
[10]
5. Multiple choice
answer below.
1 2 3 4 5 6 7 8 9 10
1.The replication of DNA takes place during: (a) anaphase; (b) telophase; (c)
metaphase; (d) interphase.
2.Meiosis occurs in the human body in: (a) all somatic cells; (b) cells of the skin; (c)
the testis only; (d) the testis and ovaries.
3.The end result of meiosis is: (a) four daughter cells identical to the parent cell. (b)
four daughter cells, each with the diploid number of chromosomes. (c) two daughter
cells, each with the haploid number of chromosomes. (d) four daughter cells, each
with the haploid number of chromosomes.
4.In late prophase of meiosis 1 which of the following occurs? (a) Chromosomes
become visible as single threads. (b) By a process of synapsis, homologous
chromosomes form bivalents which exchange segments of chromatids. (c)
Homologous chromosomes line up on the equator of the cell. (d) Replication takes
place so that each chromosome is made up of two chromatids.
5.Which of the following statements is correct? (a) Crossing over occurs in prophase
1 of meiosis and in metaphase of mitosis. (b) DNA replication occurs once prior to
mitosis and twice prior to meiosis. (c) Mitosis results in daughter cells, identical to the
parent cells. (d) Synapsis occurs in prophase of mitosis 1.
6.A karyotype is: (a) all the genes in an organism; (b) the arrangement of a complete
set of chromosomes in each body cell; (c) both the above; (d) neither of the above.
268
7.The bivalents line up randomly at the equator of a cell in metaphase. This is known
as: (a) crossing over; (b) chromosome mutation; (c) independent assortment; (d)
segregation.
8.The process of crossing over involves the: (a) exchange of pieces of chromosome
in a homologous pair; (b) exchange of centromeres in a homologous pair; (c)
exchange of pieces of chromatids in a homologous pair; (d) exchange of pieces of
the X and Y chromosomes.
9.Crossing over is very important as it leads to: (a) variation of the gametes; (b)
independent assortment of the chromosomes; (c) the production of twins; (d)
reducing the chromosome number to half.
10.For an organism with a diploid number of 6, how are the chromosomes arranged
in metaphase 1 of meiosis 1?
[10]
3.3 Genetics and genetic engineering
What is genetics?
Genetics is a branch of biology that studies heredity and variation in organisms. It

tries to explain both the similarities and the differences between parents and their
offspring. Parents always produce offspring that look like them in some ways but
differ in other ways. Why?
heredity = passing on of traits/characteristics from one generation to the next
Who was the ‘Father of Genetics’?
Gregor Mendel (1822–1884), an Austrian monk, lived at about the same time as
Charles Darwin, but the two men never met. Mendel, often called the ‘Father of
Genetics’, was responsible for the first major breakthrough in the study of heredity
by investigating the transfer of characteristics from one generation to the next. He
realised that ‘something’ is passed on from parent to offspring and that sexual
reproduction combines these ‘somethings’ from each parent to produce offspring
which are unique, yet the same.
In 1866 he published his work but it was not recognised in scientific circles until
1900, years after his death. As Darwin’s theory of evolution was gradually accepted
so were Mendel’s findings and laws. Many other biologists used Mendel's research
as a basis for their own studies and Mendelian genetics is studied and taught
throughout the world. Gregor Mendel died in Brunn on January 6, 1884.
What are the ‘somethings’?

269
We now know that the ‘somethings’ which are passed from parent to offspring
are genes (although Mendel called them ‘factors’), which are part of DNA molecules
in chromosomes. In recent years spectacular advances have been made in
understanding the structure and functioning of these genes.
Did you know?
The amount of genetic material does not necessarily reflect the level of advancement
of an organism. For example some ferns have over 600 chromosomes and the lung
fish, a very primitive animal, has forty times more DNA than we have. This is
because they have a large number of repetitive DNA molecules.
The study of genetics involves learning almost a new language. So, before
trying to understand what Mendel did with his pea plants, try to learn the following
new words.
Genes and alleles
Genes
Each chromatid is made up of one, helical DNA molecule.
Each DNA molecule is made up of a series of genes.
A gene can be defined as a section of DNA (series of nucleotides/bases) that

controls a hereditary characteristic (trait), i.e. it is the basic unit of heredity in living
organisms.
Two chromatids of a chromosome DNA
Each chromosome has between several hundred and several thousand genes. The
total number of genes in humans is thought to be between 20 000 and 25 000. It was
previously thought to be between 30 000 and 40 000 or even higher.
Nearly all somatic cells have an exact copy of all the genes in that
organism. Mature red blood cells have no nuclei, therefore no chromosomes and no
genes. Why?
Because there are two of each kind of chromosome (paternal and maternal), each
cell contains two of each kind of gene (before replication). These versions of a
gene are known as alleles. See page 164.
The gene pool is the set of all genes, or genetic information, in a population of
sexually reproducing organisms. A large gene pool indicates high genetic diversity
and increased chances of survival. A small gene pool indicates low genetic diversity
and increased possibility of extinction.
270
How active are genes?
Although each cell contains a full complement of DNA, only the genes that are
needed are activated and the others are suppressed. Therefore, different genes are
activated in different cells, creating the specific proteins that give a particular cell
type its character, e.g. bone cells, brain cells, skin cells, etc.
Some genes play a role in early development of the embryo and are inactive
thereafter.
Some genes are active in many types of cells, making proteins needed for basic
functions. These are called ‘housekeeping genes’. Other genes, however, are
inactive most of the time.
A high proportion of genes are non-coding genes, i.e. they do not code for proteins
and occur in-between the coding sections. Only about 2% of our DNA codes for
proteins.
Note:
Master control genes that determine the way in which the body develops from a
single zygote are called hox genes.
The control of genes is called epigenetics. The Human Epigenome Project aims to
document what switches genes on or off.
Alleles
Alleles are genes responsible for controlling different versions of a

trait/characteristic found in the same locus (position) on homologous
chromosomes, e.g. for the gene determining coat colour in cattle, one allele could
determine a black coat (B) and another allele a white coat (b).
allele = one of two or more forms of a gene (from the word, allelomorph, meaning
‘alternative form’)
How are alleles represented?
When describing characteristics, alleles are represented by means of letters. Very

often the capital letter denotes the dominant allele and a lower case of the same
letter represents the recessive allele. Try to choose letters where the capital letter
differs from the small letter (not S – s), e.g. in cattle the letters could be:
B – black coat (dominant)
b –white coat (recessive)
How are alleles passed from parent to offspring?

271
Alleles are passed from parents to offspring by way of chromosomes in
the gametes that are made by the process of meiosis in the sex organs.
gamete = a reproductive cell/sex cell
Study the following diagram very carefully to make sure you understand exactly
what happens to a pair of homologous chromosomes and an associated pair of
alleles (B and b) during meiosis.
A summary of meiosis to show how the alleles are segregated
To sum up:
Normal body cells (somatic cells) are diploid (2n) as they have:
a pair of homologous chromosomes
two alleles which may be the same or different.
Sex cells (gametes) are haploid (n) as they have:
one of a pair of homologous chromosomes
one of each pair of alleles.
What happens to the gametes?
During fertilisation a male gamete, with its alleles, fuses with a female gamete, with
its alleles, to form a diploid zygote. This divides and divides by mitosis to form an
entire new organism made up of cells, each with the same set of chromosomes
and alleles as in the zygote.
Genotypes and phenotypes
A genotype is made up of all the genes an organism carries on its chromosomes

which it has inherited from its parents.
A phenotype is the physical appearance of an organism, such as tallness, hair

colour. It is partly programmed by genes, its genotype, but also shaped by external
factors such as exercise, diet and environment.
Homozygous and heterozygous
After fertilisation the zygote, and all the cells that develop from it, will have two
alleles for each gene, one from each parent. These will be in the same locus on
each chromosome of a homologous pair.
272
If the pair of alleles at a locus are the same, the organism is homozygous for that
particular trait, e.g. in our example, both alleles will determine a black coat in cattle
(BB).
homo = same
If the pair of alleles at a locus are different, the organism is heterozygous (a

hybrid) for that particular trait, e.g. one allele determining a black coat and the other
a white coat in cattle (Bb).
hetero = different
Dominant and recessive alleles
In heterozygous pairing, one allele of a pair may be:
dominant, in that this trait is expressed in the offspring, e.g. black coat.
recessive, in that the trait is suppressed in the presence of the dominant allele and
not expressed in the offspring.
Study the diagrams below carefully to make sure you understand all about
alleles and how they are represented, dominant and recessive alleles, heterozygous
and homozygous, as well as phenotypes and genotypes.
273
To sum up:
Genotype Phenotype
BB (homozygous) black coat
Bb (heterozygous) black coat
bb (homozygous) white coat
Note that in the coat colour, there are three possible combinations of alleles
or genotypes for determining the coat colour but only two phenotypes. This is
because:
If one allele is dominant over another, a homozygous organism (BB) has the same
phenotype (in this case, black coat) as a heterozygous organism (Bb).
The allele b is recessive as its effect is hidden by the dominant B gene and its
characteristic will only be expressed in the phenotype when there is no dominant
allele present. In our example, only animals with the genotype bb – homozygous
recessive – will have white coats.
He’s not quite what we had in mind.
Learning activity 1
Genetic terms
Question 1
Match the words in the left-hand column with the definitions in the right-hand column
and write the letters of the answers in the spaces provided.
Words Definitions
1. gene A.Having two identical alleles for a particular characteristic.
2. allele B.The allele which has an effect in both homozygous and

heterozygous conditions.
3. phenotype C.Having two different alleles for a particular characteristic.
4. genome D.All the chromosomes in a cell, showing their size, number and
shape.
5. genotype E.A short length of DNA which controls an organism’s
274
characteristic.
6. karyotype F.Genetic make-up of an individual.
7. homozygous G.All of the genes of an organism.
8. dominant H.The allele which only has an effect when homozygous.
9. recessive I.A contrasting form of a gene for the same characteristic.
10. J.An organism’s outward appearance.

heterozygous
1 2 3 4 5 6 7 8 9 10 11 12
[10]
Question 2
Complete the following sentences by underlining the correct word from inside the
brackets.
1.A pea plant whose (genotype/phenotype) is tall could have the

(genotype/phenotype) TT or Tt.
2.A tall pea plant with the genotype TT is (homozygous/heterozygous) dominant.
3.A tall pea plant with genotype Tt is (homozygous/heterozygous) dominant.
4.A dwarf pea plant with the genotype Tt is (homozygous/heterozygous) recessive.
5.The complete set of genes necessary to create an organism is called a

(karyotype/genome).
6.Coat colour in some cattle is controlled by a single (allele/gene) which has two
forms, black coat and white coat.
7.After mating, fertilisation occurs and the gametes fuse to form a (haploid/diploid)
zygote.
8.1When a black-coated cow mates with a black-coated bull some of the offspring
are white-coated. The (genotype/phenotype) of the rest of the offspring is black.
8.2For the above result to have occurred, the parents must both have been
(homozygous/ heterozygous).
8.3The white colour form must be (dominant/ recessive) to the black colour form.
[10]
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Question 3
In your own words, explain the difference between each of the following pairs of
terms:
1.gene and allele (4)
2.genotype and phenotype (3)
3.homozygous and heterozygous (4)
4.dominant allele and recessive allele (4)
[15]
Total [35]
Monohybrid crosses
A monohybrid cross is a cross between parents with different alleles for a single
gene.
Before studying these crosses it is important to know how to express them. This is
done by means of genetic diagrams.
Genetic diagrams
Genetic diagrams show how characteristics are inherited. They show the genotype
and the phenotype of a cross between two parents and help us understand why the
offspring look the way they do.
Generations are shown as follows:

P1 – parent generation
F1 – first filial generation of offspring
F2 – second filial generation of offspring
Alleles can be shown as capital and small letters.

Very often the capital letter denotes the dominant allele and a lower case of
the same letter represents the recessive allele. Try to choose letters where the
capital letter differs from the small letter (not S – s), e.g. in cattle the letters could be:
B– black coat (dominant)
b –white coat (recessive)
As there are two alleles for each characteristic, one on each chromosome of a
homologous pair, two letters are written, e.g.:
– homozygous tall plant – TT
– homozygous short plant – tt
– heterozygous tall plant – Tt
What is a punnett square?

276
A punnett square is an easy way to represent a cross between two organisms for
any number of characteristics for which the parental genotypes are known. It predicts
the probability of the offspring’s genotype and phenotype and is the basic tool used
for Mendelian genetics.
The alleles of the gametes are written as shown below.
The characteristics of the offspring can be determined by combining the allele of

each gamete with the allele that intersects in each of the squares.
Note:
These ratios are likely to be achieved only when a large number of offspring are
produced.
The phenotype is determined by the alleles in each offspring square: an uppercase

letter represents a dominant allele.
The recessive allele will only be expressed in the offspring when it is homozygous,
i.e. when no dominant allele is present.
For example:
gametes T t
T TT Tt
T Tt TT
A punnett square
phenotypes: ¾ tall, ¼ short

ratio – 3:1, tall: short
genotypes: ¼ TT, ½ Tt, ¼ tt

ratio – 1: 2: 1
These ratios are likely to be achieved only when a large number of offspring are
produced.
Now you should be ready to understand what Mendel did with his peas.
Mendel’s experiments
There were a large number of pure-breeding pea plants available to Mendel in the
monastery garden and, between the years 1856 and 1863, he raised and tested over
28 000 of them, carefully analysing seven pairs of seed and plant characteristics
such as plant height, pod shape, pod colour, flower position, seed colour, seed
shape and flower colour. He was trying to establish what happens to
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the alternative forms of traits, e.g. purple and white colour in flowers, when they
are combined together to form a hybrid.
An example of Mendel’s experiment
Mendel transferred pollen grains from the stamen of a pure-breeding tall pea
plant and dusted them onto the stigma of the pistil of a pure-breeding short pea
plant (having first removed the anthers of these flowers to prevent self-pollination).
pure-breeding plants = plants that always give rise to offspring that are similar to
themselves.
He then collected and sowed the seeds.
The resulting F1 generation all grew into tall plants. It seemed as if the short
characteristic had completely disappeared in this generation of plants.
The F1 generation was then allowed to self-pollinate, creating a F2 generation.
When Mendel counted the plants in the F2 generation, he found that three quarters
of them were tall and one quarter was short. The ratio of tall plants to short plants
was 3:1. He counted thousands of plants before he came to these proportions.
It seemed that the characteristic for shortness had not completely disappeared in the
F1 generation, as it reappeared in the F2 generation. In this way Mendel’s work
showed that characteristics are passed on from one generation to another.
A genetic diagram to show monohybrid inheritance
Can you see why this is a monohybrid cross? It is a cross between pea plants
which only differ in one respect, i.e. height of plant. The two alleles are tallness and
shortness.
Complete dominance
In Mendel’s experiment on crossing tall and short pea plants, as

described, complete dominance was shown, i.e. a characteristic that is fully
expressed in the phenotype of a heterozygous organism (i.e. tallness) is
the dominant allele.
When a dominant and a recessive allele are present together, only the dominant
allele has an effect on the phenotype.
The heterozygous phenotype is the same as the homozygous phenotype with

dominant alleles, i.e. genotypes TT and Tt, both plants will be tall.
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The characteristic that is masked (shortness) when the organism is heterozygous is
the recessive allele and will only be expressed when it is homozygous, i.e. when
no dominant allele is present.
In the time since Mendel carried out his experiments on pea plants, new
technologies and methods of research have allowed scientists to refine and expand
on his work. Although he never stated his discoveries as ‘Laws’, the essence of his
basic principles of inheritance is still correct and can be summarised as follows:
Mendel’s law of segregation
During meiosis, allele pairs separate (segregate) so that the gametes have a single
allele for each characteristic.
Mendel’s law of dominance
In a cross of parents that are pure for contrasting traits, only the dominant trait will
appear in the phenotype. Recessive alleles will always be masked by dominant
alleles.
Mendel’s law of independent assortment

The alleles of different genes (e.g. height of plant and colour of flowers) segregate
randomly and independently of one another during gamete formation.
Go over these laws once more before attempting to put your knowledge into
practice.
Learning activity 2
Monohybrid crosses, showing complete dominance
Question 1
In the space on the next page draw up a punnett square to show what chance there
is that the children of a man and a woman who are both heterozygous for long
eyelashes, will have short eyelashes. The allele for long eyelashes is dominant to
the allele for short eyelashes. Below the square, write down the different ratios of the
phenotype and the genotype.
Don’t forget to write down the letters you choose for each allele.
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Phenotype:
Ratio:
Genotype:
Ratio: [11]
Question 2
So far, we have studied Mendel’s experiments and seen what happens in a cross
between two homozygous parents (TT x tt) and a cross between two heterozygous
parents (Tt x Tt), but what will happen if a heterozygous parent (Tt) is crossed with a
homozygous recessive parent (tt)? Work out the following genetic diagram. Tallness
(T) is the dominant allele.
[13]
Question 3
In rabbits, the allele for brown eyes, B is dominant to the allele for blue eyes, b.
1.What are the two possible genotypes for a brown-eyed rabbit?

(2)__________________
2.What is the only possible genotype for a blue-eyed rabbit?

(1)__________________
3.A rabbit breeder crossed a brown-eyed rabbit with a blue-eyed rabbit. The rabbits
had three babies, all with brown eyes. The breeder said this proved that the brown-
eyed rabbit must have the genotype BB, but her daughter said that she could not be
certain, and should do a cross again to make sure. Who was right, the breeder or the
daughter? Explain your answer. (3)
[6]
Question 4
A boy’s mother is able to roll her tongue, which is caused by a dominant allele R.
She is heterozygous for this trait. The boy’s father does not have the ability to roll his
tongue. Which combination of alleles could the boy inherit? Show by filling in the
diagram below how you worked out your answer. (9)
280
10.What percentage chance is there that the boy will be able to roll his tongue? (1)
_______
[10]
Total [40]
These exercises make you think but they can be great fun. Did you enjoy this
learning activity?
Learning activity 3
More monohybrid crosses
Question 1
Draw punnett squares to show the expected phenotypes and genotypes in the
offspring from a cross between a:
1.homozygous brown-eyed and a blue-eyed rabbit (4)
2.heterozygous brown-eyed and a blue-eyed rabbit (4)
3.homozygous brown-eyed rabbit and a heterozygous brown-eyed rabbit (4)
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[12]
Question 2
Using the symbols W for normal wings and w for vestigial wings (remains of wings
that were once functional), draw a genetic diagram to show what kind of offspring
would be produced if a heterozygous fly mated with one which was homozygous for
normal wings.
[10]
Question 3
Crosses Genotypes of Phenotypes with % of

F1 F1
TT x tt (two homozygous)
Tt x Tt (two heterozygous)
Tt x TT (heterozygous x dominant
homozygous)
Tt x tt (heterozygous x recessive
homozygous)
[8]
Total [30]
What is a test cross?
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If an organism shows the dominant phenotype, how do we know if it is homozygous
or heterozygous for the dominant trait? The only way to find out is to cross an
unknown dominant organism several times with an individual showing the recessive
phenotype.
If the offspring all show the dominant characteristic the organism must have
been homozygous.
If the cross yields any recessive offspring, the organism must be heterozygous.
Learning activity 4
Test crosses
Question 1
In the brown rat, a dominant allele, R, codes for resistance to the rat poison,
warfarin. The recessive allele r leads to rats which are susceptible and will
consequently die.
1.A homozygous, warfarin-resistant rat mates with a susceptible rat. What proportion
of the offspring is likely to be resistant to warfarin? (2)
2.The offspring of the above cross mate amongst themselves. What proportion of
their offspring is likely to be resistant? (2)
3.How would you discover whether a resistant male rat was homozygous or
heterozygous? (4)
[8]
Question 2
In Dalmatian dogs, the allele for black spots is dominant to the allele for liver (dark
red) spots. If a breeder has a black-spotted dog, how can she find out whether it is
homozygous or heterozygous for this characteristic? (4)
[4]
Total [12]
Sex chromosomes
Of the 23 pairs of chromosomes in a human cell, 22 pairs have more or less the
same shape, i.e. are homologous. They are called autosomes.
The two chromosomes making up the 23rd pair differ in shape and are the sex
chromosomes or gonosomes. They determine the sex of the offspring.
The longer sex chromosome is called an X chromosome.
The shorter chromosome is called a Y chromosome.
283
Females have two X chromosomes in their cells, so they have the
genotype XX (homogametic).
Males have one X chromosome and one Y chromosome in their cells, so they have
the genotype XY (heterogametic).
The sex chromosomes
Sex determination in humans
If the sex chromosomes are XX the undifferentiated sex organ (gonad tissue) in a
very young embryo will develop into an ovary and the foetus will grow into
a female.
If the sex chromosomes are XY, the presence of a gene on the Y

chromosome will trigger development of the gonad tissue into a testis and the
foetus will grow into a male.
The sex of an organism is therefore determined by the presence or absence of the

Y chromosome. This ‘switch’ occurs when the embryo is 7 to 8 weeks old. After this
many other genes, mainly on autosomal chromosomes, control the detailed
differentiation of male and female characteristics of the foetus.
Did you realise how important the Y chromosome is in the development of

boys?
Note:
In mammals, males always have XY sex chromosomes, i.e. are heterogametic.
In birds and butterflies it is the females that are heterogametic.
Inheritance of sex is a special form of monohybrid inheritance. You can work out
sex inheritance in just the same way as for any other characteristic, but using
the letters, X and Y as symbols to describe whole chromosomes instead of
individual alleles.
Learning activity 5
Inheritance of sex
Question 1
1.Name the type of cell division which results in gametes. (1)
2.If a normal human cell has 46 chromosomes, how many chromosomes are there in
a human sperm cell? (1)
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3.In a human boy:
3.1.which sex chromosome came from his father? (1)
3.2.which sex chromosome came from his mother? (1)
4.Of the two sex chromosomes, which one carries the largest number of genes? (1)
[5]
Question 2
1.Complete the following genetic diagram to show how sex is inherited, using the
symbols X and Y. (9)
Parental male female

phenotype
Parental 1. 2.
genotypes
gametes 3. 4.
Genotypes of 5.
offspring 6.
Phenotypes of 7.
offspring 8.
Ratio of 9.
phenotypes
2.As you can see, for every child born, there is a 50% chance of the child
being male or female. It depends on whether the X or Y sperm reaches the egg
(always X) first. But despite this, there are slightly more boys than girls born. Can
you suggest an explanation for this? (3) Think!
[12]
Total [17]
Sex-linked alleles
The Y chromosome is very short and has very few alleles on it other than those
responsible for ‘maleness’.
The X chromosome is much longer and can carry many alleles along its length in
addition to those for ‘femaleness’.
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Only a very small part of the X and Y chromosomes can pair up during meiosis (i.e.
have complementary genes) and no crossing over occurs.
The alleles that are carried on the non-homologous part of an X chromosome are
called x-linked genes or sex-linked alleles.
How are sex-linked alleles inherited?
Men have only one X chromosome so they will have only one of each sex-linked
allele which is carried on the X chromosome.
Women with two X chromosomes will have two sex-linked alleles; one on each X
chromosome.
Alleles on the X chromosome therefore can be inherited by either sex, but the male
can only receive one of the possible alleles.
The female, with XX chromosomes can be either homozygous or

heterozygous for the X-linked allele.
Examples of sex-linked diseases
There are more than 120 sex-linked diseases in humans such as cleft palate,
diabetes insipidus, red-green colour blindness, haemophilia and muscular dystrophy.
Certain genetic diseases seem to occur more often in males than in females. This is
because the male has only one X chromosome so, if a gene mutates or if a gene
for a disease is present, on this X chromosome, the male will get the genetic
disease. If the gene is recessive, it will only be expressed in the female if both X
chromosomes have the allele, so the chances of the female getting the disease are
less.
We will study two of these diseases, both of which are caused by recessive sex-
linked alleles on the X chromosome.
Red-green colour blindness

Haemophilia
1. Red-green colour blindness
The genes that produce photo-pigments (those that are sensitive to different
wavelengths of light) in the cones of the retina in the eye are carried on the X
chromosome. If these genes are missing or damaged, certain photo-pigments will be
affected.
More than 99% of all colour blind people suffer from red-green colour blindness.
An individual with this form of colour blindness finds it difficult to tell the difference
between various hues of red and green.
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The inheritance of colour blindness
X-linked recessive inheritance
Make sure you understand the reasoning behind each of the following facts.
Note:
The gene for red–green colour blindness is transmitted from a colour blind male on
his X chromosome, to all his daughters who become heterozygote carriers and
are usually unaffected.
The sons of an affected male will not inherit the trait from him, as they only inherit his
Y chromosome and not his defective X chromosome.
A carrier woman has a 50% chance of passing on a mutated X chromosome to each

of her sons.
A female will only be colour blind if there is a recessive colour blind allele on each of
her two X chromosomes – a rare happening.
Should an affected male have children with a carrier or colour blind woman, their
daughters may be colour blind by inheriting an affected X chromosome from each
parent.
Do you know anyone who is colour blind?
Learning activity 6
Red-green colour blindness
Question 1
1.On which chromosome are most sex-linked genes carried? (1)
2.What is a carrier? (2)
[3]
Question 2
1.Using the letters B to represent normal vision and b to represent colour blindness,
in the table below fill in five possible genotypes and the corresponding phenotypes to
represent both normal vision and colour blindness in females and males. Use the
symbols X and Y.
Genotype Phenotype
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[10]
Question 3
Red-green colour blindness is an inherited condition which causes affected

individuals to confuse the colour red and green. The table shows the approximate
percentages of red-green colour blindness in different populations.
Population Sample % colour blind

size
male female
Arbs 337 10.0 1.00
Swiss 2 000 8.0 0.64
British 16, 180 6.6 0.36
Japanese 259,000 4.0 0.16
Eskimos 297 2.5 0.06
Fiji islandders 608 0.8 0.006
1.State two general conclusions which can be drawn from this data, giving a reason
in each case. (7)
2.The table suggests that about 0.4% of women in Britain are red-green colour blind.
Use appropriate symbols to complete the genetic diagram below to show the most
likely way in which this defect arises in woman. What percentage of offspring will be
colour blind? (2+ 16+2)
[20]
Total [40]
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Did you manage to sort out the Xs and Ys and the alleles for colour blindness?
Well done if you did.
2. Haemophilia
Haemophilia is a rare, genetically determined condition of frequent, excessive

bleeding as the blood clots very slowly.
The dominant allele H allows blood to clot.
The recessive allele h does not allow blood to clot normally.
The alleles controlling blood clotting are sex-linked alleles, located on the X
chromosome. There is no gene for blood clotting on the Y chromosome.
What is the male genotype?
There are only two possible genotypes for a male as the Y chromosome does not
have a gene to code for haemophilia.
genotype phenotype
XHY normal
XhY normal but a carrier
Haemophilia is caused by a recessive allele on the single X chromosome.
What is the female genotype?
There are no known female haemophiliacs as there are no known women who are
homozygous for the recessive allele, XhXh. This is because this condition causes a
natural abortion.
Women can however be carriers of the recessive allele, h.
The two possible genotypes a female may have for the haemophilia trait are:
genotype phenotype
XHXH normal
XHXh normal but a carrier
Haemophilia is therefore a male disease.
Learning activity 7
Haemophilia
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In the case of haemophilia, what would happen if a carrier woman married a normal
man and produced children? Note the symbols used in the previous text and fill
these in the spaces below to find out. (14)
Male Female
Parental Normal man Carrier woman

phenotype
Parental genotype 1. _________ 2. ___________
Gametes 3. ___________ 4. ___________

5. ___________ 6. _____________
Genotypes of offspring 7. ___________ 8. ___________

9. ___________ 10. _____________
Phenotypes of offspring 11. ______________________________________

12. ______________________________________
13. ______________________________________
14. ______________________________________
2.What percentage of the male children would probably be haemophiliacs? (1)
Total [15]
How did you manage? Don’t forget to go over your answers carefully, correcting
any mistakes.
What is meant by polygenic inheritance?
Simple traits such as eye colour may be caused by just one pair of alleles.
In polygenic inheritance there is more than one pair of alleles responsible for a
single trait.
These more complex traits are determined by the interaction of many different
alleles, each having small individual effects on the offspring, resulting in a range of
phenotypes.
What is meant by continuous variation?
The more pairs of alleles that control a characteristic, the greater the number of
possible combinations and the greater the variety of phenotypes. Each phenotype
differs slightly from the next, forming a graduated series. This is an example
of continuous variation.
continuous variation = graduations of a characteristic in a phenotype, e.g. height in
humans
290
Examples of continuous variation
Traits such as height, skin colour, metabolic rate and longevity are usually controlled
by polygenic inheritance. Some variation in height in humans is due to environmental
factors such as diet, exercise and disease. Other examples of polygenic inheritance
include: colour in wheat kernels, egg weight in poultry and fleece weight in sheep.
Gene mutations
A mutation is a sudden change in the genetic makeup (DNA) of an organism.
A gene mutation results from a change in the sequence of nucleotides in a DNA

molecule, causing a change in the information the gene gives to the cell, i.e. the
codons will be altered which will result in a faulty protein or no protein at all being
made. See page 142 for more detail.
What are mutagens?
Mutagens factors that increase the rate of mutations, e.g. environmental factors such
as ionising radiation (e.g. ultraviolet light and X-rays), mutagenic chemicals (e.g.
formaldehyde, benzene, carbon tetrachloride) and viruses and micro-organisms.
How do mutations affect organisms?
Mutations can have a variety of different effects on organisms depending on the

type of mutation, the importance of the piece of genetic material affected and
whether the affected cells are germ cells (gametes) or somatic cells.
Somatic mutations occur in body cells and are not transmitted to the next
generation. These can cause cells to become malignant which will result in cancer.
In plants they may be transmitted by vegetative propagation such as budding.
Gametic mutations occur in the reproductive organs (ovaries, testis, anthers or

embryo sacs) and produce changes to the genes in the gametes. These mutations,
also known as germ-line mutations may lead to variation in the offspring.
Eventually by accumulating these changes, a new species may evolve, a process
called speciation. This plays an important role in evolution.
Gametic mutations may also lead to hereditary diseases.
Neutral mutations
Neutral mutations do not affect the life of the organism.
Every individual has some mutations but most of them will not be visible in the
phenotype.
Some gene mutations, however, do change the physical features of the body, but do
not seriously affect the functioning of the body, e.g. tongue rollers and non-tongue
rollers.
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Beneficial mutations
A small percentage of mutations result in a change in the phenotypes. If the change

results in organisms adapting better to new or unfavourable conditions, they will
survive and breed more successfully than the rest of the population. This is natural
selection as nature has selected the better adapted to survive and breed. In time
the whole population will have the new genotype and a new species will have been
formed, i.e. speciation has occurred which plays an important role in evolution.
Due to their rapid reproduction rate, beneficial mutations occur most often
amongst viruses and bacteria, e.g. the new multi-resistant super-bugs (bacteria)
that have mutated to become resistant to antibiotics. This is obviously harmful to
humans, but beneficial to the survival of the bacteria species!
A classic example of a beneficial mutation is the mutation of the pale form of

the peppered moth to a dark form in some parts of Great Britain during the
industrial revolution. The buildings and surroundings became grey with coal dust so
the grey colour of the moths made them less conspicuous to predators and enabled
them to survive.
Dark peppered moth on dark background
There is more information about beneficial mutations in the unit on Evolution.
Harmful mutations
The mutations we hear about most often are the ones that cause disease. Humans
have over 100 syndromes caused by chromosomal abnormalities, e.g. Down
syndrome, and more than 6 000 diseases caused by the inheritance of mutations in
single genes, e.g. cystic fibrosis, sickle cell anaemia, Tay-Sachs disease,
Huntington’s disease and colour blindness, among many others.
These diseases usually are inherited as autosomal recessive traits.
autosomal = relates to chromosomes that are not sex chromosomes, i.e. numbers 1
to 22
The heterozygous parents each have one normal copy of the gene and one mutated,
non-functional copy.
The homozygous recessive individuals exhibit the disorder because both gene
copies are non-functional and the correct gene product, a protein, is missing.
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This is one reason that marriage between close relatives is discouraged; two
genetically similar adults are more likely to pass on two copies of a defective gene to
their child.
Albinism – an example of a harmful mutation
Albinism is a rare group of inherited genetic disorders that cause the skin, hair, or
iris of eyes to have little or no colour due to partial or complete absence of the
pigment, melanin. Melanin protects the DNA in underlying tissues against the
harmful effects of UV light.
It is caused by a mutation of one of several autosomal genes that produce or

distribute melanin.
It is estimated that about one in 70 people carry the faulty gene.
Albinism shows a pattern of recessive monohybrid inheritance. The mutated allele

can pass from generation to generation and only be expressed in the phenotype of
the offspring if both parents have the recessive mutated gene. Individuals may have
a normal phenotype but be carriers of the gene, in which case they are not affected
by the condition and have a normal amount of melanin.
carrier = has a recessive allele and a dominant allele in each cell, therefore has a
normal phenotype.
If both parents carry the gene, there is a one in four chance that their child will have
albinism and a one in two chance they will be a carrier.
Is life difficult for an albino?
Albinism is usually not life-threatening, but as the skin of an albino is extremely

sensitive to the sun, they are vulnerable to sunburn and cancer which makes
working outdoors virtually impossible. But the challenges confronting albinos do not
end there: all too often they are shunned, discriminated against and mocked by their
peers. Some people believe that giving birth to an albino is the result of a curse or
bewitchment in the family. Despite attempts to promote understanding, many albinos
still face prejudice and ignorance from the wider community and lead lonely lives. It
is important that we all make every effort to protect them against such behaviour.
Genetic counselling is important. By studying a family tree the counsellor may be

able to predict whether a couple is likely to have a child with albinism. In a pedigree
chart albinism occurs infrequently, often skipping one or more generations
altogether.
Note:
An albino may be able to produce more vitamin D than normal. Why?

293
Africa has the highest prevalence of albinism in the world, with about one per 4 000
to 5 000 people being affected. Denmark has one in 60 000.
Albinism occurs in a large number of animals but it is not common in the wild.
Why do you think albinism is rare in the wild?
Learning activity 8
Mutations and albinism
Question 1
1.What is a mutation? (2) __________________
2.What is a mutagen? (2)__________________
3.Mention two examples of mutagens. (2) __________________
4.A mutation may be caused by a change in the chromosome or a change in the

gene. Gene mutations affect two different kinds of cells. Name these cells. (2)
__________________
5.Why is a mutation in an egg or sperm more harmful than in a body cell? (2)
__________________
[10]
Question 2
Underline the correct word from inside the brackets in the following sentences
relating to albinism. (10)
1.Albinism is an example of a (chromosome/gene) mutation.
2.Albinism is an (heritable/non-heritable) disease.
3.Albinism is caused by lack of the pigment (tyrosine/melanin).
4.Melanin is formed by the amino acid (tyrosinase/tyrosine)
5.Melanin protects the body against the harmful effects of (ultraviolet rays/infrared
rays) of the sun.
6.People living in Nigeria will produce (more/less) melanin than people living in
England.
7.Albinos in the wild are (less/more) vulnerable to predation than normal animals.
8.Which parts of the body are not affected by albinism? (eyes/fingernails/skin/hair).
9.Avoiding light because it hurts the eyes is called (photophobia/photogenic).
10.Denmark has a (higher/lower) incidence of albinism than Africa.

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[10]
Total [20]
Don’t forget to correct your mistakes, then re-read the corrected sentences to
learn from your mistakes.
Single Nucleotide Polymorphisms
Single nucleotide polymorphisms (STP) are genetic variations in a DNA sequence

that occur when a single nucleotide is substituted for another nucleotide. SNPs are
considered to be point mutations that have been evolutionary successful enough to
recur in a significant proportion of a population of a species.
SNPs occur throughout the human genome—about one in every 300 nucleotide
base pairs. This means that there are about 10 million SNPs within the 3-billion-
nucleotide human genome. Modern insights into these genetic variations are
changing the understanding of inheritance.
Most commonly, these variations are found in the non-coding DNA between genes.
They can act as biological markers, helping scientists locate genes that are
associated with disease.
What is a genome?
A genome is the complete set of genetic instructions (genes) necessary to create

an organism.
Nearly every somatic cell in the body has a complete copy of a genome. Each
species has a unique genome although the genome of individuals of the same
species may vary slightly due to mutations.
The Human Genome Project
The Human Genome Project (HGP) is an international scientific research project

set up in 1990. The primary goal was to:
determine the sequence of chemical base pairs which make up human DNA (DNA
sequencing)
identify and map all the genes of the human genome from both a physical and a
functional point of view.
Did you know?
Humans only have 1% of unique genes, i.e. genes that we do not share with other
species.
295
As researchers learn more about the function of genes and proteins, this knowledge
will have a major impact in the fields of medicine, biotechnology and life sciences.
More than 1 800 genes causing diseases have already been discovered, e.g. the:
BRCA2 gene associated with increased risk of breast cancer.
Apo-E gene linked to Alzheimer’s disease.
LDL receptor gene linked to bad cholesterol and heart disease.
Many ethical, legal and social issues have arisen since the human genome was
sequenced, e.g. patenting of genes or creating designer babies.
Learning activity 9
Ethical problem concerning the HGP
Read through the following passage and answer the questions that follow on
foolscap paper.
Patenting of genes
Dr Lydia Mendoza and her company, Genmania, have spent years working to
identify how the gene for albinism works. Identifying the gene would open the door to
curing the condition. Finally, her team succeeds.
But the years spent on research were expensive. One way to make back that money
is to patent the gene that team members just identified. Then, anyone who wanted to
develop either treatments or tests would have to pay a fee to use the gene.
When a patent is submitted to the government, the company must prove that the
item to be patented is original and patentable.
Write your answers on a separate sheet of paper.
1.What do you think about patenting a gene that already exists in the human body?
2.Should the government allow this gene to be patented? Why or why not?
3.Some think that genes should not be patented as they are a medical discovery and
not an invention, and everyone should be allowed to use the information without
paying. What do you think?
4.If, in the future, Genmania develops a test for this gene, should they be allowed to
patent the test? Why or why not?
What is genetic counselling?
Genetic counsellors are health professionals with specialised graduate degrees

and experience in the areas of medical genetics and counselling. They usually work
as part of a healthcare team and through genetic counselling they provide
information and support to families who have members with birth defects or
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genetic disorders, such as Down syndrome, Huntington’s disease, physical
handicaps, deafness, cancers, etc. As the hereditary (or genetic) conditions may be
passed on from parent to children, many genetic diseases or disorders tend to run in
families. Counsellors, therefore, study family and medical histories to analyse
inheritance patterns and the risks of the problem recurring.
Genetic counselling also aims to provide families with options as to the best way
to manage the disorder and can refer families or individuals to appropriate social
support structures.
What sort of issues could be discussed?
Here are some questions that could be discussed with a genetic counsellor:
Should a couple have children if both are ‘carriers’ of a faulty gene, or should they
adopt a child?
Is artificial insemination by a donor or embryo donation a practical alternative to the

problem?
Is in vitro fertilisation and the testing of embryos prior to implantation a possible

option?
Should cousins contemplate having children?
What is a family tree?
In humans the pattern of inheritance of a particular characteristic is investigated by

researching a family pedigree, if appropriate records of the ancestors exist.
A family tree shows both the genotypes and phenotypes of several generations of
individuals in a family. Individuals may have a normal phenotype but be carriers of a
genetic disorder, with the mutant allele being recessive.
How are family trees useful?
Many disorders are caused by genes that are not functioning properly. These genes
can be passed on from generation to generation. A family tree can be constructed to
predict whether a couple is likely to pass on a genetic disorder. For example, if a
couple gives birth to a child with a disease such as cystic fibrosis, they can arrange
to see a genetic counsellor.
In trying to work out the chance of their next child being born with the disease, the
genetic counsellor must know as much as possible about the parents’ genetic make-
up. This information is then used to build up a family tree to show how certain
features are inherited and whether they may occur in the next generation.
An example of a family tree
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The family tree below shows the occurrence of night blindness in the males and
females of a family over three generations.
Take careful note of the key to fully understand this diagram.
A family tree to show night blindness in a family
This type of night blindness which makes it difficult to see in dim light is controlled by
two alleles. The allele for night blindness is dominant to the allele for natural
vision.
Family trees
Question 1
The family tree below shows the inheritance of sex-linked colour blindness in a
family. By using the key below, fill in the possible genotypes of all the family
members. (8)
[8]
Did you remember that males only have one X chromosome?
Question 2
The family tree below shows the inheritance of cystic fibrosis in one family. Cystic
fibrosis is caused by a recessive allele.
1.Select letters to represent the normal and cystic fibrosis alleles. (2)
2.Give the genotypes of each of the people named in the family. (6)
Take note of the children produced by the parents to work out the genotypes of the
parents.
Name Genotype
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3.What are the possible genotypes of the unnamed son of Jane and Daniel? (2)
4.If Jane and Daniel have another child, what is the probability of it being:
4.1 completely normal __________________
4.2 a sufferer from cystic fibrosis________
4.3 a carrier of the disease? (3) __________________
5.After the discovery that Ingrid had cystic fibrosis, Jane and Daniel went to see a
genetic counsellor. What would have been the purpose of such a visit? (2)
_________________
[15]
Total [23]
Genetic engineering
Genetic modification has been taking place naturally over the centuries. New
species evolved and are evolving due to natural mutations. Today, however, man
is playing an ever increasing role in altering the genomes of organisms
by biotechnological processes, in a process called genetic engineering.
genetic engineering = any direct manipulation of an organism's genes
biotechnology = using scientific procedures to influence specific processes in living

organisms which will benefit humans or improve the environment
Genes may be turned on or off, deleted or deactivated or foreign genes inserted into
chromosomes - the possibilities are endless.
Genetic engineering is currently the fastest growing branch of modern genetics.

Although certain aspects of it are causing concern regarding ethical and
environmental issues, it is proving to be very beneficial in many different fields.
Genetic engineering may be one of the greatest scientific breakthroughs in

recent history.
Recombinant DNA technology
There are many different ways of transformation, one of which is recombinant

DNA technology. This is a form of biotechnology that is used to introduce new,
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beneficial genes into an organism to create genetically modified organisms
(GMOs).
recombinant DNA = a form of DNA that does not exist naturally but is created by
combining DNA sequences that would not normally occur together
genetically modified organism (GMO) = an organism with introduced foreign DNA

(gene) that results in new and useful traits
In its simplest forms recombinant DNA technology involves finding a desirable

gene and moving it into the cells of another organism by means of a vector.
vector = a virus (bacteriophage) or plasmid that transfers foreign genetic material

into another cell
plasmid = a circular, double stranded DNA molecule found in bacterial cells that are
not part of the bacterial chromosome
Bacterium showing plasmids
The new organism will then follow the instructions of the inserted gene and make the
protein for which the new gene codes.
If the genes are placed into bacteria, the bacteria can then be cultured to produce
many working copies (clones) so that large quantities of the desired protein are
produced.
Examples of proteins made by recombinant DNA technology
Protein Used in treatment of...
human growth hormone pituitary dwarfism
interferon hepatitis B and C, some cancers, multiple sclerosis
factor VIII haemophilia B
The manufacture of human insulin
The manufacture of biosynthetic ‘human’ insulin was one of the biggest

breakthroughs in recombinant DNA technology.
Insulin is a hormone which lowers the glucose sugar levels in the blood. A diabetic
cannot produce sufficient insulin which results in too much glucose in the blood. To
counteract this, a regular dose, injection or nasal spray of insulin is often essential.
How does this process take place?
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Very briefly, this is brought about as follows:
1.DNA with the gene that codes for insulin production is removed from healthy
human pancreatic cells.
2.Restriction enzymes cut these DNA strands at specific sites to isolate the gene
that codes for insulin.
3.Escherichia coli (E. coli), bacteria found in the human digestive tract, are the
'factories' used in the genetic engineering of insulin. A plasmid, removed from E.
coli is cut open by restriction enzymes. Its uneven, cut ends are called sticky
ends.
4.The enzyme ligase joins the piece of DNA carrying the gene that codes for insulin,
into the bacterial plasmid to form recombinant DNA.
ligase enzyme = occurs naturally in the nuclei of cells and acts as ‘genetic
glue’, joining together the ends of two single strands of DNA
Now do you understand what recombinant DNA is?
5.The plasmid with its recombinant DNA acts as a vector and is re-inserted into the
host cell, E. coli bacterium, which will be effectively re-programmed to produce the
protein, insulin. The E. coli bacterium is therefore a genetically modified organism.
6.The bacteria are kept in huge tanks containing a nutrient medium (fermentation
broth) with the optimum pH, temperature and nutrient values, where they reproduce
rapidly producing vast numbers of bacteria, each with the new gene capable of
producing insulin. In this way the new gene is cloned and enormous amounts of
insulin are produced which are purified and sold.
cloning = is the process of artificially reproducing a gene, set of genes, or a whole

organism
The commercially available human insulin is indistinguishable from pancreatic

human insulin.
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The advantages are that the insulin:
is produced rapidly in large quantities.
is relatively inexpensive.
has few side effects as it is ‘human’ insulin.
Note:
Yeast cells may be used in recombinant DNA technology as they also have
plasmids. The advantages are that yeast cells are more readily available and more
cost effective than E. coli.
Recombinant DNA technology
Question 1
Read the following passage about genetic engineering and answer the questions
that follow.
Genetic engineering allows scientists to transfer genes from one organism to

another. Simple, rapidly reproducing organisms like bacteria can be used as
chemical factories for making substances needed by humans.
Insulin, secreted by the pancreas, is responsible for causing glucose to be absorbed

into the liver from the blood. Diabetics (Type 1) cannot make their own pancreatic
insulin and therefore have to have daily injections of this hormone, usually taken
from animals. However, animal insulin differs slightly from the human variety and
sometimes has unpleasant side effects.
Scientists can now produce human insulin by means of genetic engineering. They
transfer the human insulin gene from human cells to the bacterium, E. coli by using
special enzymes.
The bacteria reproduce to form millions of cells, all able to make human insulin.
These bacteria can be grown in huge numbers in large vats. Now diabetics no longer
have to use insulin from animals.
1.What technique do scientists use in the artificial production of insulin? (2)
2.Which organ of the body secretes insulin? (1)
3.What is the effect on the body of an insulin deficiency? (2)
4.Why is insulin extracted from animals, not ideal for treating human diabetics? (2)
5.What is the abbreviated name of the bacterium used in the production of insulin?
(1)
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6.Why is it significant that bacteria reproduce very rapidly? (2)
[10]
Question 2
Fill in the missing words to complete this diagram to illustrate how insulin is produced
by genetic engineering. (6)
[6]
The principle of genetic engineering is illustrated here by insulin production
Total [16]
Now you should know all about recombinant DNA technology!
Gene therapy
Gene therapy is an experimental genetic engineering technique that replaces a

faulty gene or adds a new gene in an attempt to cure disease or improve the body's
ability to fight disease, i.e. if a mutated gene causes a necessary protein to be faulty
or missing, gene therapy may be able to introduce a normal copy of the gene to
restore the function of the protein.
How are new genes introduced into the body?
Vectors such as viruses are used to deliver the gene into the cells of the body. The
viruses are treated so they cannot cause disease in the patient.
Delivery may be:
1. Direct delivery
The vector can be injected or given intravenously (by IV) directly into a specific
tissue in the body, where it is taken up by individual cells.
2. Cell-based delivery
A sample of the patient’s cells can be removed and exposed to the vector in a
laboratory setting. The cells containing the vector are then returned to the patient. If
the treatment is successful, the new gene delivered by the vector will make a
functioning protein.
Figure 11.1. Strategies for Delivering Therapeutic Transgenes into Patients

(© 2001 Terese Winslow)
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Gene therapy may be used in the future for treating a wide range of diseases
including cancer, cystic fibrosis, heart disease, diabetes, haemophilia and AIDS.
Researchers must, however, overcome many technical challenges before gene

therapy will be a practical approach to treating disease. For example, scientists
must:
find better ways to deliver genes and target them to particular cells.
ensure that new genes are precisely controlled by the body.
Genetically modified crop plants
For thousands of years genetics has made an impact on agriculture. By means

of artificial selection, farmers can control the reproduction of their plants so that
each new generation has as many of the parents’ beneficial genes as possible. This
is a form of selective breeding which is a kind of genetic engineering. By selective
breeding, the yield of the major cereal crops has been increased, crops have
become more resistant to disease and the nutritional value of fruits and vegetables
has been enhanced.
Why are crops genetically transformed?
transformation = the change in a cell or organism brought about by the uptake of

introduced, foreign DNA
Conventional plant breeding methods can be slow and unpredictable. By genetic

engineering, the exact desired trait can be created in one generation with great
accuracy.
Conventional plant breeding can only combine closely related plants. What genetic
engineering of plants enables scientists to do is to take any gene from any living
organism and introduce it into a plant.
The resulting transformed or transgenic plant is referred to as a genetically

modified organism (GMO) and the inserted gene is called a transgene.
transgenic organism = an organism that develops from a cell with recombinant DNA
Is genetic engineering a modern development or based on indigenous knowledge?
The indigenous knowledge of how to manipulate crops, how to conserve genetic

resources and how to improve the diagnosis and treatment of plant and animal
diseases has been passed down from generation to generation.
Transgenic technology enables plant breeders to identify and isolate genes that
control a specific trait from a wide range of living sources and artificially insert them
into other organisms which will then have the required traits. This has enabled plant
breeders to do what they have always done – generate more useful and
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productive crop varieties containing new combinations of genes. This is done,
however, in a much faster and more controlled way than by traditional cross-
pollination and selective breeding techniques.
On the one hand therefore genetic engineering and conventional agricultural

methods may be seen as complementary.
On the other hand, transgenic technology may be seen as a dramatic departure from
conventional agriculture, since it gives scientists the power to move genetic material
between organisms that could not be bred through conventional means.
To achieve useful results, therefore, it needs both the indigenous knowledge of

classical plant breeding methods as well as the information derived from genomics.
How are plants transformed?
There are two main methods of transforming plant cells and tissues:
1.The ‘gene gun’ method (also known as microprojectile bombardment or biolistics

method) is a technique that has proved quite effective in plant engineering. In this
technique, pellets of metal (usually tungsten) coated with the desirable DNA are fired
into plant cells. Those cells that take up the DNA may be cloned and then allowed to
grow into new plants, producing vast numbers of genetically identical crop plants.
2.Recombinant DNA techniques have allowed a much more controlled way of

introducing new genetic material into the plants, as described below.
Transformation using T1 plasmid
The T1 plasmid from soil bacteria, Agrobacterium tumefaciens, causes tumours

(galls) in plants.
Crown gall caused by

Agrobacterium tumefaciens
The fact that these bacteria have the ability to invade and naturally infect plant cells
has been used as a way of inserting transgenes into plants cells as follows:
1.The T1 plasmid is removed from the bacterium and a restriction enzyme cuts the
plasmid.
2.The enzyme ligase splices the gene of interest, the transgene, into the plasmid to
form a recombinant plasmid.
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3.The plasmid is introduced into a plant cell and the part with the gene
becomes integrated into the cell’s chromosomal DNA.
4.Transformed plant cells are grown by tissue culture.
5.Finally they are planted out to grow normally.
6.The transgenic plants then have to be extensively tested by growing them

under different environmental conditions to ensure that the transgene has no
detrimental effects on other plant functions or on the quality of the product and to
check the overall performance of the plants.
Geneticists world-wide are working to introduce new genes into crop plants to make
them more productive.
What is plant tissue culture?
Plant tissue culture is widely used to produce clones of a plant in a method known
as micropropagation. It is a technique used to grow lots of plants from tiny pieces
from the parent plant in sterile agar jelly with plant hormones and nutrients.
Tissue culture involves the following steps:
1.Small amounts of parent tissue or a number of cells are taken.
2.The plant material is transferred to plates containing sterile nutrient agar jelly.
3.Plant hormones are added to stimulate the cells to divide.
4.Cells grow rapidly into small masses of tissue.
5.More growth hormones are added to stimulate the growth of roots and stems.
6.The tiny plantlets are transferred into potting trays where they develop into plants.
What is polyploidy?
Polyploidy is a condition of having more than the basic two copies of chromosomes.
It is especially common among ferns and flowering plants.
It may occur through hybridization between two species, resulting in new species
(speciation) which makes it very important in the evolution of new species of plants,
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e.g. bread wheat (6n) which is one of the most important food sources today, arose
from two separate events of hybridization. Many other cultivated plants are
polyploidy, e.g. bananas are triploid, potatoes are tetraploid, some strawberries are
octaploid.
Through biotechnology many species of polyploidy plants will have:
larger flowers, e.g. marigold, snapdragon
larger fruits, e.g. watermelons
larger storage organs, e.g. potatoes
seedless fruits, e.g. banana, grapes
resistance to disease, e.g. tobacco resistant to mosaic virus infection.
Genetically modified crops and polyploidy
Question 1
Genetic engineering plays a very important role in agriculture. Using magazines, the
internet or any other sauce, list six genetically modified crops and state the
advantages of each. Write them in the table on the next page.
Crops Advantage
Question 2
1.n what bacteria do T1 plasmids occur? (1)
2.When these plasmids invade plant tissue, what do they cause? (1)
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3.Name two enzymes that are important in the recombinant DNA technique as
described above. (2)
4.Mention three conditions that are necessary to make plant tissue culture
successful. (3)
5.Polyploidy is particularly successful in which two plant groups? (2)
6.Besides natural replication processes and abnormal meiosis, what other process
causes polyploidy? (1)
[10]
Total [22]
What are the advantages of GM crops?
It has been calculated that, if we continue with current agricultural practices, Africa,
south of the Sahara, will have a grain shortage of 88.7 million tons by the year 2025.
What can be done? Using GM crops will:
give increased yields which will help to solve the world's hunger and malnutrition
problems.
help protect and preserve the environment by reducing reliance on chemical

pesticides and herbicides.
Overall, therefore, genetic engineering has enabled new traits in important

agricultural crops to improve their:
resistance to pests and herbicides e.g. introduction of Bt bacteria into cotton, maize
and potato plants. (Bt bacteria produce a protein that kills certain insects.)
nutrient value, e.g. golden rice. (Genes from carotene-producing plants are
introduced into rice which can form vitamin A when the rice is eaten.)
taste and quality, e.g. new species of tomatoes
resistance to weather extremes.
GM crops are now grown in over 40 countries on six continents.
Something extra……
Resurrection plants
A group of scientists from the Department of Molecular and Cell Biology at the
University of Cape Town, Kenyatta University in Kenya and the CSIR in Pretoria are
all working on developing drought tolerance in a number of important African crops.
Genes from an indigenous ‘resurrection plant’ are being used. These plants are
able to survive on only 5% of their water content – they appear to be dead. When
water returns, however, they can resurrect within 72 hours and appear very much
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alive again. The idea is to introduce genes from these plants into maize so that this
vital crop can become resistant to drought.
Imagine being able to revive a ‘dead’ organism!
What are the disadvantages of GM crops?
Because of the potentially huge benefits to be gained from the use of GMOs, there is
great pressure to continue producing them. There are many concerns, however,
about ethical and environmental issues regarding the use of GMOs.
The major concerns centre on:
potential danger to the environment
possible health risks to humans
economics.
Genetically modified crops:
are costly to produce as they involve modern biotechnology which requires highly
skilled people and sophisticated and expensive equipment.
may include a pesticide-resistance gene that unintentionally harms wild life and
disrupts food webs, e.g. the Monarch butterfly being affected by GM crops.
are a threat to biodiversity of wild species. GM crops with new traits could be
grown on such a large scale that they destroy the habitats of wild species.
could be more vulnerable to climate change, pests and diseases if grown as a

monoculture.
can interbreed with wild plants and spread to future generations in an

unpredictable uncontrollable way, e.g. a gene for resistance to adverse conditions
might be transferred from a crop plant into a weed species.
if ingested by animals (especially humans), may disrupt normal gene function,

causing diseases such as cancer.
may be harmful to some, e.g. new proteins causing allergies in humans.
Economically, one of the objections to GMOs is that they put power, money and
control of our food supply in the hands of a few big companies. The problem is that
only these large companies have the resources to afford the expense, legal
exposure and regulatory system involved in bringing GMOs to the market.
Conclusion: Further studies are needed to assess the potential risks of GM foods
even though the technology promises many benefits. Until further studies can show
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that GM foods and crops do not pose serious threats to human health or the world’s
ecosystems, the debate over their release will continue.
How safe is food derived from GM crops?
Each application for a commercial release of a crop is assessed by the Genetic

Resource Centre of the Department of Agriculture. Foodstuffs that are currently
made of genetically modified crops (mainly maize, soybean and rape) have been
judged safe to eat, and the methods used to test them approved.
However, the lack of evidence of negative effects does not mean that new
genetically modified foods are without risk. The possibility of long-term effects from
genetically modified plants cannot be excluded and must be examined on a case-by-
case basis. New techniques are being developed to address concerns, such as the
possibility of the unintended transfer of antibiotic-resistance genes.
Some ethical questions
Genetic engineering touches on many moral issues, particularly involving religion.
Does man have the right to manipulate the laws and change the course of nature?
Who will be responsible for deciding what is safe and what is not?
Can ‘new’ organisms be patented? Who will own the beneficial gene combinations?
Will developing countries become more and more dependent on the wealthier
countries for food?
Will governments be able to implement the biosafety protocol? See later.
Is it right that agriculture is increasingly being controlled by a few giant biotechnology

corporations?
If a large part of the funds made available for genetic engineering were diverted to
solve the more basic problems of housing, health and nutrition worldwide, would the
money not benefit far more people immediately?
It is so important to discuss issues. This is the way you learn and it helps you to
make up your own mind.
How is the release of GMOs controlled?
In South Africa there is a Genetically Modified Organisms Act administered by the

Department of Agriculture. They have the responsibility of considering each
application for a field trial or commercial release on a case-by-case basis.
Contravention of the Act can result in a fine or imprisonment of up to four years.
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In September 2003 the biosafety protocol, a subsidiary agreement to the UN
Convention on Biological Diversity, came into force.
It is designed to regulate the international trade by monitoring the handling and

use of any genetically engineered organism that may have adverse effects on the
conservation and sustainable use of biological diversity, taking into account risks to
human health.
The protocol requires that countries are informed and agree in advance to imports of
GE crops. This is called the Advance Informed Agreement (AIA). Before countries
are allowed to export any genetically engineered organisms destined to be
introduced into the environment, they must first obtain the importing country's
consent, e.g. Zimbabwe recently refused GM wheat/maize.
The biosafety protocol is a historic achievement. For the first time under international
law, there is an explicit requirement that countries take precautionary measures to
prevent GMOs from causing harm to biodiversity and human health.
One hundred countries have signed the agreement. The US, Argentina and Canada
governments have not ratified the protocol, despite the fact that these countries
produce some 90% of GM crops in the world.
What about environmental watchdogs?
Environmental watchdogs such as Biowatch and SafeAge (South African Freeze

Alliance on Genetic Engineering) are NGOs, established in the late 1990s to
publicize, monitor and research issues of genetic modification, and to promote
biological diversity. Their role is very important in making the government and the
public aware of potential problems related to GMOs.
The creation of GMOs, however, creates extreme reactions and a balanced

approach should be encouraged.
Consumers should weigh up the pros and cons of GMOs and not be kept in the dark
by those in power and by large corporations which may not have the general public’s
interests as their primary goal.
In conclusion
Genetic engineering may offer opportunities for increased production, productivity,

product quality and adaptive fitness, but they will certainly create challenges for the
research and regulatory capacity of developing countries to avoid causing
unintended harm to human health and the environment as a result of enthusiasm for
this powerful technology.
Genetic engineering
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These excerpts, in the adjacent column, are taken from an article which appeared in
a South African newspaper in February 2001. Answer the questions that follow.
‘Mankind will have the ability to control and alter its evolutionary destiny within 30
years, using secrets
unlocked by the mapping of the human genetic code’, says Dr. Francis Collins,
director of the Human Genome Research Institute in the United States.
By 2010, scientists will have developed accurate tests for a dozen common genetic
illnesses, and preventive treatments to match, he predicted.
By 2020, doctors will be able to alter the genes passed on to children, leading to the
first genetically engineered human beings.
By 2030, genetic medicine will mean most Britons will live to the age of 90.
However, he cautioned against humans relying too much on genetic manipulation.

‘The well-heeled couple who decide they want to use genetics to have a child that is
a gifted musician may end up with a sullen adolescent who smokes marijuana and
doesn’t talk to them.’
But he said that advances in screening technology, genetic engineering and new
therapies to repair defective genes will allow medical researchers to eradicate DNA
variations that cause fatal diseases such as Huntington’s chorea, a neurological
condition and muscular dystrophy, a wasting disease.
It will be possible for mankind to set its own evolutionary path and build a ‘fitter’
species he said.
‘I wouldn’t be surprised if, in another 30 years, some people will begin to argue that
we ought to take charge of our own evolution and should not be satisfied with our
current biological status and should, as a species, try to improve ourselves.’
1.Of which institute is Dr Francis Collins director? (2)
2.Dr Collins said that in 30 years time, man will be able to control his evolutionary
destiny. What will make this possible? (2)
3.By the year 2010, preventive treatment will be available for how many different
genetic diseases? (1)
4.What progress with regard to genetically engineered humans will have been made
by the year 2020? (2)
5.In this article, mention two fatal diseases which are caused by defective genes that
genetic engineering could help to eradicate. Which tissue of the body does each
disease destroy? (4)
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6.Do you think we should be satisfied with our current biological status or do you
think we, as a species, should try to improve ourselves? (5)
7.Two advantages of genetic engineering are mentioned in this excerpt. What are
they? (4)
Total [20]
Hope the exercise made you think about the future!
Class debate on the hazards of genetic engineering
Select four speakers; two to support the ideas put forward in the following statement
and two to oppose it. Draw out of a hat as to which group supports and which group
opposes. Each pair is given time to draw up its arguments and conclusions. When
both pairs have expressed their opinions, the rest of the class votes as to whether
they agree or disagree with the statement.
Living organisms are complex and tampering with their genes may have unintended
effects. It is in our common interest to support concerned scientists and
organisations, such as Friends of the Earth who demand ‘mandatory labelling of
these food products, independent testing for safety and environmental impacts and
liability for harm to be assumed by biotech companies.’
Genetic engineering
Genetic engineering may be one of the greatest scientific breakthroughs in recent

history and is currently the fastest growing branch of modern genetics. Although
certain aspects of it are causing concern regarding ethical and environmental issues,
it is proving to be very beneficial in many different fields.
On A4 paper, write a mini-essay on how you feel about the pros and cons of genetic
engineering and how it will affect our lives in the future.
Total [20]
Cloning
Cloning describes the processes used to create an exact genetic copy of another
gene, cell, tissue or organism. The copied material, the clone, has the same genetic
makeup as the original.
Cloning in animals
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Cloning by nuclear transfer
In recent years clones have been produced using embryonic and non-
embryonic nuclear transfer techniques.
1. Embryonic nuclear transfer
This process has been used successfully for many years in sheep, using cells
taken directly from early embryos.
This type of cloning can produce:
many transgenic animals with very precise genetic qualities as rapidly and cheaply
as possible. These valuable animals can then become part of commercial herds.
many clones from a single female to conserve animals nearing extinction.
early embryos from which stem cells can be isolated for use in tissue and cell
engineering.
2. Non-embryonic nuclear transfer (somatic cell transfer)
Dolly, the Dorset lamb born at the Roslin Institute in Scotland, was the first mammal
to be cloned from non-embryonic cells.
In a process called ‘somatic cell nuclear transfer’ (SCNT), scientists transfer

genetic material from the nucleus of a donor adult cell to an egg whose nucleus, and
thus its genetic material, has been removed.
An electric pulse is used to combine the dormant donor cell and the recipient egg
cell.
The reconstructed egg containing the DNA from a donor cell must be treated with
chemicals or an electric pulse in order to stimulate cell division.
Once the cloned embryo reaches a suitable stage, it is transferred to the uterus of a
female host where it continues to develop until birth.
The resulting offspring is a clone of the somatic cell donor. Study the diagram below
very carefully.
Imagine being able to have genes for ‘intelligence’, ‘artistic ability’ or ‘good
looks’ inserted into gametes – the implications are vast!
Why is this procedure so significant?
This procedure proved that the genetic material from a specialized adult cell, such as
an udder cell of a cow, programmed to express only those genes needed by udder
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cells, could be re-programmed into an embryonic state to generate an entire new
organism not just udder tissue.
Cloning
1.Define the term cloning. (3)
2.Explain how each of the following is controlled in the nuclear transfer process:
2.1.The switching off of all genes in the donor cell. (1)
2.2.The fusion of donor cell with the de-nucleated egg cell. (1)
2.3.The activation of the reconstructed cell to produce an embryo. (1)
3.Describe two potential applications of nuclear transfer technology for the cloning of
animals. (3x2)
Total [12]
Class discussion
Each of the following statements is controversial and should provide interesting

topics for discussion in class.
Should ‘embryo banks’ be established from which prospective parents could select a
child with desirable genetic traits?
Destroying an 8-cell embryo produced in a laboratory is not an abortion.
Societies should be able to clone and reproduce individuals with traits for specific
purposes, e.g. academics, artists, musicians, soldiers.
Hope the exercise made you think about the future!
What are the disadvantages of cloning?
The most controversial aspect of cloning is the potential to clone humans which
creates enormous moral and ethical concerns, e.g. cloning humans could result in:
the creation of groups of people for specific purposes, e.g. warfare or slavery.
attempts to improve the human race according to an arbitrary standard.
clones being created for the sole purpose of using their organs and tissues for
transplants.
the death of many embryos and newborns because the techniques have not been
perfected.
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In addition, cloning reduces genetic diversity by reducing the gene pool. This could
weaken a population’s ability to adapt to its surroundings.
It is not legal to engineer human germ cells but imagine being able to have
genes for ‘intelligence’, or ‘good looks’ inserted into gametes!
Artificial selection
This topic has been very well covered in the unit on ‘Evolution by natural
selection’, page 230.
Report
Using books, magazines and the internet write a report on one of the following
topics:
the human genome project
cystic fibrosis - a genetic disease
The report should be written in essay form; well-constructed and informative and not
longer than one and a half A4 pages.
Short questions
1. Multiple choice
answer below.
1 2 3 4 5 6 7 8 9 10
11 12 13 14 15 16 17 18 19 20
1.Genetics is the study of: (a) mechanisms of inheritance; (b) development of

organisms; (c) variation of species; (d) nuclear divisions.
2.Alleles are: (a) different forms of a gene; (b) the total number of genes on one
chromosome; (c) a homologous pair of chromosomes; (d) two genes on the same
chromosome.
3.A recessive allele: (a) has the same effect on the phenotype as a dominant allele;
(b) has its effect hidden by a dominant allele; (c) only effects the phenotype when it
is heterozygous; (d) has no effect on the phenotype.
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4.An allele which has an effect in both homozygous and heterozygous conditions is
called: (a) lethal; (b) recessive; (c) multiple; (d) dominant.
5.The outward appearance of an organism is known as: (a) phenotype; (b) genotype;
(c) karyotype; (d) genome.
6.Which step is not true in a somatic cell nuclear transfer process? (a) the genetic
material originates from a embryonic donor cell. (b) an electric pulse stimulates the
donor cell nucleus and recipient cell to fuse. (c) chemicals or another electric pulse
then stimulate cell division. (d) the embryo is transferred to the uterus of a female
host to develop until birth.
The following three questions refer to Mendel’s experiments using pea plants, where
the allele for tallness, T, is dominant.
7.Pure-breeding, tall pea plants are crossed with pure-breeding short pea plants.
The resulting F1 offspring are all tall. Which of the following terms best describes this
F1 generation? (a) heterozygous, with shortness dominant; (b) heterozygous, with
tallness dominant; (c) homozygous for tallness; (d) homozygous for shortness.
8.The tall offspring in question 7 were allowed to self-pollinate. What percentage of

the next generation would you expect to be tall? (a) 25%; (b) 50%; (c) 75%; (d)
100%.
9.A tall pea plant was crossed with a short pea plant. About half of the offspring were
tall and half were short. What were the genotypes of the parents? (a) TT x Tt; (b) Tt x
Tt; (c) TT x tt; (d) Tt x tt.
10.A homozygous red-flowered snapdragon is crossed with a homozygous white-

flowered snapdragon. The F1 generation, which produce pink flowers only, is
allowed to self-pollinate. If 20 of the F2 offspring have white flowers, approximately
what will the number and phenotype of the remainder of the F2 plants be? (a) 10
plants with red flowers; (b) 10 plants with pink flowers; (c) 20 plants with red flowers
and 20 with pink flowers; (d) 20 plants with red flowers and 40 with pink flowers.
11.Single nucleotide polymorphisms are: (a) short tandem repeats; (b) polymerase
chain reactions; (c) a substitution of a single nucleotide in a DNA molecule; (d) none
of the above.
12.A zygote with XX gonosomes: (a) is haploid; (b) will develop into a baby girl; (c)
will develop into a baby boy; (d) cannot exist.
13.Which of the following genetic disorders is caused by a chromosome mutation?

(a) sickle-cell disease; (b) albinism; (c) haemophilia; (d) Down syndrome.
14.Which disorder is due to mutations in sex linked alleles? (a) albinism; (b) cystic
fibrosis; (c) red–green colour blindness; (d) sickle-cell disease?
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15.Cloning describes the processes used to create an exact genetic copy of: (a) a
gene; (b) a cell; (c) an organism; (d) all the above.
16.In genetic engineering, DNA may be changed by: (a) Adding a foreign gene from
another species. (b) Altering the degree to which a gene is turned on or off. (c)
Deleting or deactivating a gene to prevent it from expressing. (d) All of the above.
17.In genetic engineering, a strand of DNA is cut into pieces to isolate a specific
gene by: (a) ligase enzymes; (b) restriction enzymes; (c) plasmids; (d) ‘sticky end’
enzymes.
18.Which of the following statements is incorrect with regard to recombinant DNA

technology? (a) It allows certain hormones to be produced in large quantities. (b) It
can produce tomatoes which have a longer shelf-life. (c) It enables various crops and
vegetables to be more drought resistant. (d) A section of mRNA with the desired
gene is spliced into a cut plasmid.
19.In South Africa, the following have been genetically modified to be herbicide- and
insecticide-resistant except for: (a) soybeans; (b) rice; (c) cotton; (d) canola.
20.Which statement is incorrect with regards to polyploidy? (a) Bananas are triploid.
(b) Potatoes are tetraploid (c) strawberries are octaploid. (d) Bread wheat is triploid.
[20]
and 2) and a statement in the second column. Decide which item(s) relate to the
statement and write down your choice using the following codes:
C if both items 1 and 2 relate to the statement
D if neither item 1 or 2 relate to the statement
Item Statement
1. 1. genome a complete set of chromosomes in one cell

2. karyotype
2. 1. Agrobacterium bacteria used in recombinant DNA technology

tumefaciens
2. Escherichia coli
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3. 1. polyploidy more than one pair of alleles responsible for a
2. polygenic single trait
4. 1. olour blindness autosomal gene disease

2. haemophilia
5. 1. albinism caused by chromosome mutations

2. own syndrome
6. 1. gene therapy cloning

2. somatic cell nuclear
transfer
7. 1. restriction enzyme acts as glue to stick pieces of DNA together

2. ligase enzyme
8. 1. bacteria have plasmids and act as vectors

2. yeast cells
9. 1. direct delivery gene therapy

2. cell-based delivery
3. Mix and match
Column A Column B
1.sex cell A.Banded patterns of DNA
2.somatic cell B.Genetic factors present in an organism
3.haemophilia C.Agrobacterium tumefaciens
4.mutation D.23 pairs of chromosomes
5.vectors E.Introduction of healthy genes to cure a genetic

disease
6.gene therapy F.Sex-linked disease
7.genetic fingerprint G.Small ring of DNA in bacteria
8.genotype H.Carry genes into target cells
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9.tumour-forming I.23 chromosomes
bacteria
10.plasmid J.Change in the genetic make-up of an organism
[10]
In each case, write down whether the statement is true or false. If false, write down
the incorrect and correct words.

word word
1.Pure-breeding plants result from a cross between

heterozygous parents.
2.If an X sperm fertilises an egg, the resulting zygote

will develop into a baby boy.
3.There are 23 pairs of autosomes in each cell and one

pair of gonosomes.
4.Red-green colour blindness is particularly common in

men.
5.What an organism looks like is called its genotype,

and this is controlled by both genes and the
environment.
6.A plasmid is a ring of RNA found in bacteria.
7.Gene mutations can be caused by crossing over,

replication or transcription.
8.Haemophilia is caused by lack of an autosomal

recessive mutated allele.
9.The manufacture of biosynthetic ‘human’ insulin is

brought about by recombinant DNA technology.
10.Plasmids and viruses both act as vectors in

recombinant DNA technology.
[16]
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5. Terms
1.A segment of a DNA molecule which determines a particular characteristic.
2.Different forms of the same gene, situated on the same locus of homologous
chromosomes.
3.A thread-like structure made up of DNA and protein.
4.A genotype consisting of different alleles for a specific characteristic.
5.A genotype consisting of two identical alleles for a specific characteristic.
6.A genetic cross involving one characteristic.
7.Describes a characteristic that will not appear in the phenotype when present
in the heterozygous condition.
8.A computerised diagram to show all the chromosomes in a cell.
9.The appearance of an organism due to its genetic make-up.
10.A major change in the structure or distribution of one or more chromosomes.
11.Ring-like structures of DNA in bacteria.
12.DNA formed by combining a segment of DNA from one source into the DNA
of a host cell.
13.The process of inserting foreign genes into an organism.
14.Organisms used to transfer genes into target cells.
15.The complete set of genetic instructions (genes) necessary to create an

organism.
16.A structure that shows both the genotypes and phenotypes of several
generations of individuals in a family.
17.The set of all genes, or genetic information, in a population of sexually

reproducing organisms.
18.The sequencing of chemical base pairs which make up human DNA.
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19.Occurs when one nucleotide is replaced by another which occurs in a
significant proportion of a population of a species
20.Graduations of a characteristic in a phenotype.
[20]
Evolution
Note:
Throughout this module, dates will be shortened as follows:
4.5 billion years ago – 4.5 bya
3 million years ago – 3 mya
A little of what was learnt in Grade 10 …
Before you start this module, it is vital to remember what you learnt in grade 10.
The universe started 13.7 bya because of the Big Bang – the most widely accepted
current theory of the universe’s origin.
Did you know that all the hydrogen the earth has today came from that
occasion, since then no more hydrogen has been made. Therefore, we contain
molecules that are 13.7 million years old.
The earth is very, very old – so old that it is difficult to imagine: 4 550 million (4.6
billion) years old.
Earth’s crust has been built up in layers over millions of years. The layers have
been successively laid down either by water (sedimentary rocks) or by volcanic
activity (volcanic rocks). Each layer is therefore of a different age, oldest layers at the
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bottom.
Layers of the earth’s crust
Dating of fossils – relative dating and radiometric dating (absolute dating) can
determine the age of a rock layer, and therefore the age of fossils embedded in that
rock.
At least five mass extinctions have occurred, with many species becoming extinct;
250 mya 90 percent of life disappeared; 65 mya dinosaurs disappeared.
By studying fossils one:
-learns about ancient forms, e.g. trilobites, and the appearance and extinction of
organisms, from individual species to whole taxonomic groups, e.g. the dinosaurs.
-understands that life-forms changed and gradually became more similar to present-
day life-forms.
-gains evidence to support the idea that species change, i.e. have undergone
evolution.
South Africa is very rich in fossils with some important finds, for example:
-earliest organisms (3.5 bya), stromatolites (fossilised Cyanobacteria) – Barberton in

Mpumalanga
Stromatolites, formed from layers of blue-green algae
-primitive land plants, e.g. a fern, Glossopteris – KwaZulu Natal
Glossopteris leaves
-coelacanth, – a fish group ancestral to amphibians
Coelacanth
-mammal-like reptiles – a bridge between reptiles and mammals – Karoo
4.1 Origin of an idea about origins
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Development of the theory of evolution
What is evolution?
Evolution is the gradual change or development of something. It can be used in

various senses in social or economic structures and general use, e.g. a book tracing
the evolution of the English language.
What is biological evolution?
Biological evolution is the change in the gene pool of a population during the
course of time by such processes as mutation, natural selection and genetic drift.
Biological evolution, simply put, is descent with modification. This definition covers
micro-evolution (evolution within a species) and macro-evolution (the decent of
different species from a common ancestor over many generations). Evolution helps
us to understand the history of life.
Learning activity 1
Biological evolution
Without using words, devise a learning diagram to show what is meant by biological
evolution.
Why is it so important that we know about biological evolution?
Biological evolution:
has become the unifying concept that acts as a foundation for understanding all
Biology.
supports and explains many aspects of our everyday lives.
challenges people to really think for themselves.
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How did life originate?
The origin of life on earth has been a source of speculation among philosophers,
religious thinkers and scientists for thousands of years. While there have been
various theories, the current scientific opinion is that there was a single origin of
life – this idea is supported by the fact that all life shares the same genetic code and
similar basic enzymes but science is still a long way off from explaining how life
originated. What is certain is that life on earth appeared very early – about 3.7 mya.
It is worth noting that Darwin’s ideas about evolution cannot explain the origin of
life: they don’t even try to.
How did species diversity originate?
There have been many ideas about how species diversity arose.
A. Before 1700
Before 1700 most scientists accepted that:
species were unrelated and remained unchanged, i.e. they were fixed since they
were created by a divine power.
the earth was young, perhaps only 6 000 years old, and static (unchanging).
B. 1700 to early 1800
From 1700 to early 1800 a few creative thinkers, including Erasmus Darwin,
Charles’s grandfather and Jean-Baptiste Lamarck began to challenge these
concepts. Through the study of the fossil collections and being aware of the huge
diversity of living organisms they became convinced that:
species had changed gradually over time.
the earth was millions of years old rather than only a few thousand years old.
Erasmus Darwin
Erasmus Darwin (1731 – 1802) was a successful country doctor as well as a

scientist, philosopher, inventor, poet and author. In his famous
book, Zoonomia (1794, 1796) he put forward the idea that life on earth descended
from a common ancestor. In addition, he suggested that species must have
changed (or evolved) over time but he offered no mechanism for what he termed
‘transformation’ (evolution).
Jean-Baptiste Lamarck
Jean-Baptiste Lamarck (1774-1829), a French naturalist, about a decade later, put

forward his ideas on evolution in his book Philosophie Zoologique (1809). Lamarck,
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like Erasmus Darwin, proposed that species were not fixed. He reached this
conclusion as a result of making various observations such as:
living species are different to fossil types, so life forms must have changed over time.
domestication and selective breeding resulted in animals and plants changing.
cross-breeding of plant species often led to new characters appearing.
How did Lamarck suggest that species changed?
Lamarck proposed that change was a natural phenomenon and not a result of divine
intervention. He suggested that organisms changed during their lifetime so that they
could survive in new environments and that these acquired changes were then
passed on to offspring.
His hypothesis on how change took place was as follows:
Use and disuse of body parts
Lamarck believed that when the environment changed the organism would actively
respond by changing so it could adapt to the new environment. For example, the
more organs were used the more they would increase in size or efficiency. If not
used, they would get smaller and eventually disappear
Inheritance of acquired characteristics
These physical (phenotypic) changes or characteristics acquired by parents during

their lifetime were then passed on to their offspring. In this way, populations changed
and new species were formed.
This hypothesis was known as the inheritance of acquired characteristics (often
called ‘soft’ inheritance or Lamarckism).
Some examples of Lamarckism
Lamarck considered that the long neck and legs of the modern giraffes were the
result of generations of short-necked and short-legged ancestors stretching their
necks to feed on leaves at progressively higher levels. He thought that the acquired
characteristics, longer legs and a longer neck were passed on to the offspring of
each generation until eventually a new species of giraffe with a very long neck and
long legs appeared.
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Inheritance of acquired characterstics
Was Lamarck’s mechanism for evolution correct?
Lamarck’s belief that the environment can produce phenotypic changes in an

individual was correct, but he was incorrect in thinking this caused evolutionary
change. For example, bodybuilding exercises will increase the size of muscles.
However, this acquired characteristic, whilst influencing the phenotype, does not
alter the genotype of egg cells or sperm cells. Therefore, the characteristic acquired
during life cannot be passed on to the offspring, i.e. it is not heritable.
It must be remembered that at that time nothing was known about genetics and how
characteristics are transferred from parents to their offspring. It was only in the
1930s, thanks to work done by Mendel in the late 1800s, that the transfer of
characteristics by genes became known.
To sum up:
In contrast to many of their contemporaries both Erasmus Darwin and Lamarck

believed that:
species have common ancestors
evolution occurred as species adapted to their environment.
For those interested look up ‘Epigenetics and Lamarkism’ on the Internet – a

whole new hypothesis!
C. Early 1800 to early 1900
A convincing mechanism for evolution had yet to be discovered. It was because of

the work of Charles Darwin and Alfred Russel Wallace during this period that an
acceptable mechanism was put forward.
Charles Darwin
Charles Darwin (1809-1882) had begun formulating his theories in the late 1830s
after a five-year expedition on the HMS Beagle to the southern hemisphere. During
the voyage he visited many countries and islands where he studied, observed and
documented vast amounts of information about their geology, biogeography and
fossils.
Charles Darwin
The data he collected made him aware of the:
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immense diversity among organisms, both living and extinct. How did these
species come about?
variation of individuals of the same species, suggesting species were not

unchangeable.
often puzzling distribution of different species. Why, in different countries, were

there different species in similar climates?
From his interest in geology, influenced by Charles Lyell’s Principles of Geology,

Darwin realised that:
the earth is extremely old which allowed time for species to evolve. He could see
these changes in fossils from the different sedimentary rock layers.
there has been great geological change over time with different areas and land
masses becoming isolated.
isolation leads to species changing.
After returning to England, Darwin worked for about 25 years developing his theory
on how evolution happens. Information both from his trip and from selective
breeding of pigeons and other domestic animals gave him clues to the process of
natural selection. (See later.)
The long time he took before presenting his ideas to the public was due to his
wanting to make quite sure that his ideas were correct. At last, in 1859 he clearly and
logically put forward his hypotheses in his famous book, The Origin of Species. It is
worth noting that the publication of his ideas was a very courageous act as Darwin
chose to say ‘no’ to the current belief of species fixity and divine creation. Even today
there are some people who disagree with him.
Darwin’s ideas in The Origin of Species, one of the most influential scientific books of
all time, changed biology forever as they were the first acceptable explanations of
two vitally important hypotheses:
1.Modification with descent (or evolutionary change) – a historical fact. In the

first half of his book Darwin gave rational explanations with plenty of evidence (see
later) to show that the diversity of species is a result of evolution, i.e. species had
modified gradually from ancient ancestors unlike themselves.
2.Natural selection – a mechanism causing evolution The second half of the book
deals with natural selection. This was Darwin’s greatest contribution to science and
is an explanation of how evolution takes place. The essence of natural selection is
that individuals best adapted to the environment will leave the most offspring.
Natural selection will be discussed in the next unit.
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It is now known that the idea of natural selection is correct, but it is not the only
mechanism of evolution.
How did Darwin explain descent with modification?
The following is the basis of his explanation.
All related organisms descended from a common ancestor.
The ancestral species spread into a variety of new habitats. Because they adapted
to the new local conditions they became modified and thus diversified into new
species, often over millions of years.
The diversification was by branching, i.e. the ancestral species gave rise to two or
more new related species, each in a new habitat. Darwin did not accept Lamarck’s
‘arrow of complexity’ – simple forms changing into complex forms, through the
history of life. He preferred the idea that diversification happened by branching, like a
tree with a trunk and branches.
Some species died out, i.e. became extinct, which can be seen in the fossil record.
Alfred Russel Wallace
Alfred Russel Wallace (1823-1913), a British naturalist, collector of wildlife

specimens and author, accepted the concept of evolution.
Alfred Russel Wallace
As a young man, he did fieldwork in the Malay archipelago. During the late 1850s he
noticed and puzzled over the seemingly illogical distribution of organisms in the
north-western (Sumatra and Java) and the south-eastern (New Guinea) parts of the
archipelago. He noticed that organisms in the former were more like those on the
Asian mainland, while those in the latter were more like those in Australia. For more
information and map, see page 209.
He suggested that the ancestors of the modern species would have become isolated
from each other by water and in the course of time evolved differently, even though
they lived in similar climates.
However, what caused the descendants of the ancestral species to change into the
modern forms still needed to be answered.
An amazing co-incidence
While looking for an explanation about how evolution might have happened, Darwin
and Wallace had independently read an article, An Essay on the Principle of
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Population (1797) by Thomas Malthus. The essence of Malthus’s essay was that
competition and thus a struggle for existence existed between members of a
population.
This influenced both men and led them, quite independently, to come up with similar
ideas about the mechanism of evolution, i.e. natural selection.
Wallace put forward his ideas in a paper that he sent to Darwin in 1858, asking for
his comments and also for his assistance in getting it published.
Darwin was amazed to realise that Wallace’s hypothesis on the mechanism of

change was nearly the same as his. This lead to Darwin and Wallace publishing a
joint paper, and spurred Darwin into completing his book and getting it published the
following year.
Therefore, in scientific historical records, if not in the popular awareness, Wallace

and Darwin share the reputation for having discovered natural selection.
The fact that Darwin gained greater credit for the theory is responsible as he
developed it in more detail and was responsible for it being accepted.
Note:
It took time for the central ideas of The Origin of Species to be accepted. However,
within a few decades, most scientists acknowledged that evolution and descent of
species from common ancestors was correct.
Natural selection however, had a harder time finding acceptance. In the late 1800s,
many scientists who called themselves Darwinists actually preferred a Lamarckian
explanation for the way life changed over time. It took the discovery of genes and
mutations in the twentieth century to make natural selection not just attractive as an
explanation, but a realistic one.
Learning activity 2
Development of the theory of evolution
1.Before the 1700s, how did naturalists think species arose? (1)
2.How old was the earth then considered to be? (1)
3.Jean-Baptiste Lamarck was one of two well-known, creative naturalists in the

1700s who suggested that species do change over time. Who was the other? (1)
4.These two men had seen large fossil collections. How did this influence their
thinking about the age of the earth? (1)
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5.The essence of Erasmus Darwin’s views on evolution is contained in the following
passage from his book Zoonomia. To most people at that time this was a radical
suggestion.
‘that in the great length of time, since the earth began to exist…would it be too bold
to imagine, that all warm-blooded animals have arisen from one living
filament…possessing the faculty of, and of delivering down those improvements by
generation to its posterity’.
By quoting from the text, mention three main aspects of Darwin’s views on the theory
of evolution. (3)
6.Apart from his observations of plant crossbreeding and domestication of animals,

what observation lead Lamarck to realise that species changed? (1)
7.Give the name of Lamarck’s hypothesis of how species change. (1)
8.Why do we now know that his hypothesis was not correct? (2)
9.Charles Darwin and Alfred Russel Wallace based their thinking about evolution on
two ideas of earlier naturalists. One idea was that change had occurred over time.
What was the other? (1)
10.Mention at least three observations made by Darwin that were very important and
relevant to his thoughts on how species arose. (3)
11.Darwin learnt that the earth was very much older than previously thought. Why
was this valuable to his thinking on evolution? (1)
12.He also learnt that the continents and oceans had changed dramatically. What
did this suggest to him about species diversity? (2)
13.Mention the observation and its conclusion that gave Wallace the idea that
species might evolve over time. (2 + 2)
14.When looking for an idea to explain how species change, both Darwin and
Wallace were inspired by reading a publication by whom? (1)
15.What concept in the above publication gave them the basis for the idea, that later
became known as natural selection? (2)
Total [25]
Evidence for the theory of evolution
Today it is accepted that evolution has occurred and is still happening. This is well
supported by multiple lines of evidence from:
1.Fossil records
2.Biogeography
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3.DNA (genetics) and molecular biology
4.Homologies and comparative anatomy (Grade 11)
5.Embryology
6.Vestigial organs
7.Biodiversity (Grade 10)
8.Physiology
Using a combination of the above sources of information, scientists have been able
to:
develop detailed histories of the evolution of life forms.
demonstrate the evolutionary relationships among organisms that are currently alive
(extant).
Diagram showing different sources of evidence to explain evolution of life

forms and evolutionary relationships
It is important to realise that, while evolution is accepted as a fact, the mechanisms

by which it occurs are only partly understood and are still being researched and
expanded, adding to Darwin’s ideas of natural selection.
1. Fossil evidence indicates that

evolution has occurred
Fossils found all over the earth are a significant source of evidence for evolution.
This is known as palaeontological evidence and shows both micro-evolution and
macro-evolution.
palaeontology = study of prehistoric life
The rock record is 3.5 billion year old. This extremely long period is long enough for
even the most improbable of events, such as rare mutations, to have occurred
repeatedly, and for biological evolution to have taken place.
Using radiometric dating that dates the rocks the age of fossils can usually be
worked out.
How does the fossil evidence show that

evolution has occurred?
The fossil records provide detailed information and evidence of systematic change
through time – of descent with modification. Different fossils are found in the
different rock layers with the oldest fossils in the oldest layers.
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Different fossils in the different rock layers
Modern species can be traced back through time as they show similarities with fossil
species that became extinct over hundreds of thousands of years ago.
A classic example of this is the development of the modern horse and its adaptation
over time to changing environments. It is one of several examples for which there is
a fairly complete sequential record because all the main stages of the evolution of
the horse have been preserved in fossil form.
Over 60 million years, the horse evolved from a four-toed, dog-sized ancestral
species that lived in rainforests into a one-toed animal that stood two metres tall and
was adapted to living on the plains.
Horse evolution
What can be seen in the fossil record?
Fossil records indicate that evolution has taken place as they show:
a.increase in complexity: simplest organisms appeared first
b.increase in diversity
c.more extinct species as one moves back in time
d.existence of intermediate forms between groups (transitional fossils )
e.overall increase in size, from a starting point of tiny unicellular organisms
a. Increasing complexity over time
When the full range of fossils is arranged in order of age, a succession of changes is
seen. These changes gradually accumulated over the generations. Fossils of the
simplest (earliest) organisms are found in the oldest rocks and progressively gave
rise to more complex (later) organisms, which are found in the newer rocks.
The table below on the next page shows evidence of this trend. First, there are the
fossils of earliest group, the prokaryotes (bacteria), 3.6 bya. Then slowly, in
sequence, other groups appeared – eukaryotes, invertebrates, fish, land plants,
amphibians, reptiles, mammals and finally humans. With all these changes over time
evolution must have occurred.
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Please realise that many, many simple organism are still around and are
thriving, e.g. bacteria, fungi, single-celled algae. This shows that ‘simple’ doesn’t
mean the organisms cannot be successful.
Simpler to more complex … Millions of years since first-known

appearance (mya) – approx
Earth began 4600
Oldest fossils, prokaryote cells, e.g. 3600

cyanobacteria
Oldest eukaryote cells 200
Multicellular eukaryotes 1500
Simple animals (invertebrates) and 600

plants (algae)
Fish andland plants (ferns) 450
Amphibians 350
Reptiles and cone-bearing plants 250

(gymnosperms)
Birds 150
Mammals and flowering plants 100

(angiosperms)
Modern humans (Homo sapiens) 0.2
What is the Cambrian explosion?
Beginning some 545 million years ago, a rapid diversification over a relatively short
period of five million to ten million years led to the appearance of a huge diversity of
complex, multi-celled organisms. Before this time most organisms were simple,
composed of individual cells occasionally organised into colonies. This period, the
Cambrian period is the time when most of the modern major marine groups of
animals first appear in the fossil record.
Learning activity 3
Fossils – simple to more complex
Using information from the above table, answer the questions that follow.
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1.How long ago did the first eukaryote cells appear? (1)
2.It took approximately another 1 400 million years for algae to appear. What vitally
important process do algae carry out? (1)
3.Ferns reproduce by spores and cone-bearing plants, e.g. pine trees, by seeds.
Which do you think is the more complex form of reproduction? (1)
4.Approximately how long was it from the time the first multi-cellular eukaryotes
emerged to when the first land animals arose? (1)
5.Suggest any two reasons why mammals are more highly evolved than reptiles.(2)
6.According to the above table, how much longer have reptiles been on the earth
than mammals? (1)
7.According to fossil evidence, how can we tell that birds arose after reptiles? (1)
8.How many years ago did modern humans arise? (1)
9.Give one reason why you think flowering plants are reproductively more complex
than cone-bearing plants. (1)
Total [10]
b. Increase in diversity
Today there are an estimated 1.4 to 1.7 m species of organisms – plants, animals,
fungi and micro-organisms. This poses many questions such as:
Has this immense biodiversity always existed?
If not, how did it come about?
If we are only one of the 1.4 million species how important is humankind?
Makes one think, doesn’t it?
The immense modern biodiversity has not always existed. The oldest fossil-bearing
rocks contain a small diversity of fossilised organisms while in younger (later) rocks
there is an enormous diversity.
Evolutionists believe that newer organisms descended from common ancestors,

which adapted to a variety of environments. After accumulating adaptations the
ancestors formed, by branching, a variety of modified descendants. This type of
descent is known as cladogenesis. As this pattern repeated itself, biodiversity
increased.
From the fossil remains, it is possible to see when new species arose and when
ancestral species became extinct.
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Cladogram to show common ancestor
cladogram = a family tree that shows evolutionary relationships
Think of descent in terms of a branching tree. The trunk represents the

common ancestor, changes and division of species cause the branches of the tree
and recent further changes and division form closely related species, the twigs.
Learning activity 4
Increase in diversity
1.How can we tell from fossils that there has been an increase in multi-cellular
diversity over time? (1)
The graph below clearly shows the increase in diversity (number of families). Answer
the questions that follow.
2.From what age did diversity start increasing rapidly? (1)
3.What was this sudden increase in diversity known as? (1)
4.Approximately how many families of multi-cellular species were there 480 million
years ago? (1)
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5.What do you notice about the peaks in the extinction graph line? (1)
6.How can you determine, by looking at the diversity line (number of species) when
mass extinctions occurred? (1)
7.Approximately how many more families of species are there today than there were
200 mya? (1)
8.What approximate percentage of families disappeared with the first very big mass
extinction? (1)
Total [8]
What do you think is happening to the diversity graph line in present times, and
why?
Novelties or key innovations
The fossil record shows in some instances when the diversification into new genera
and species occurred as a result of the development of novelties or key innovations
(something new and original), e.g. bony skeleton, four limbs, amniotic egg, wings,
hair, etc. in vertebrates. These evolutionary changes and evolutionary relationships
are shown in the cladogram (phylogenetic tree) below. One can see how a
cladogram is constructed by looking at the development of novelties.
Cladogram of vertebrates
c. More extinct species as one moves

back in time
Extinction, usually a natural phenomenon, is extremely important in the history of life.

Species become extinct because they have not adapted to changing conditions. New
species, which are better adapted will survive and replace them, filling the niches left
vacant. In turn, these new species die out giving rise to yet later forms. Over time,
the process is repeated again and again.
Darwin and other scientists interpret this finding as evidence that species are not
fixed, but undergo change and evolve into different species.
It has been estimated that a typical species becomes extinct within one million to ten
million years of its first appearance. There are some species, however, ‘living
fossils’, that have survived virtually unchanged for hundreds of millions of years, e.g.
the coelacanth.
Because of the huge passage of time since the first forms appeared, more species
are extinct than exist on earth today; it is estimated that 99.9% of the species that
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have ever lived on earth are now extinct. The hundreds of thousands of fossils that
have been recorded allow us to reconstruct the change or evolution in the major
phyla and other taxonomic groups.
Mass extinction events account for the large proportion of species that have become
extinct, but not all of them.
d. Intermediate forms between groups
–
transitional fossils
Transitional fossils have a mixture of traits that show a link between groups and, as
such, are often referred to as ‘missing links’. They suggest that one group may have
given rise to the other by evolutionary processes. They are therefore further
evidence of modification by descent, showing evolution caught in the act.
The fossil record has many examples of these transitional (intermediate) forms.
Mammal-like reptiles, a group of fossils found abundantly in the Karoo, are

intermediate between reptiles and mammals.
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A well-known example is Archaeopteryx, a vertebrate with both reptilian and bird
(avian) features. You would have researched Archaeopteryxin Grade 10.
Fossil and model of Archaeopteryx
Does evidence from fossils provide
conclusive proof of evolution?
In many ways the fossil record is somewhat biased and incomplete because:
very few individuals become fossils.
hard-bodied organisms are more likely to form fossils.
most fossils are of aquatic animals.
Nonetheless, the fossils that have been discovered are enough to give detailed
information and evidence of regular change through time, i.e. of descent with
modification.
In addition, from this huge body of evidence, it can be predicted that no reversals will
be found in future fossil studies. This means that organisms will never appear in
reverse order, for example amphibians will not appear in the fossil record before
fishes nor mammals before reptiles, and no complex life will occur before the oldest
eukaryotic unicellular organisms.
Learning activity 5
Fossil evidence for evolution – large number
of extinct species, transitional fossils
1.How long does the average species exist before going extinct? (1)
2.Why are there more extinct fossil species than species alive today? (3) Use
arithmetic reasoning.
3.What does this tell us about species fixity? (1)
4.What is a ‘living fossil’? Mention an example. (2)
5.Why are transitional fossils so important when trying to show that evolution
occurred? Mention an example. (3)
6.In terms of evolution, what do you suggest was the importance of extinctions?
Explain your answer. (2)
7.Most fossils are of aquatic organisms. Why? (2)
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Total [14]
2. Evidence from biogeography to show evolution has occurred
Biogeography is the study of where species (both present-day and extinct) occur,
and why. The conventional explanation that species had been created with
adaptations to their particular climate made no sense to either Charles Darwin or
Alfred Russel Wallace. They had noticed during their various voyages that different
regions with similar climatic conditions contained very different animals and
plants.
Darwin was so struck by this that he used biogeographical patterns as one of his
principal proofs of his theory of evolution.
What were these evolutionary patterns?
The patterns Darwin and Wallace observed were:
a clustering pattern of ‘closely allied’ species inhabiting neighbouring patches of

habitat. Such closely allied species tend to be found:
–within the same group of oceanic islands, e.g. the tortoises of the Galapagos
–on the same continent, e.g. several species of zebras in Africa and two rhea
species in adjacent areas of South America.
Mountain zebra
Burchell’s (Plains) zebra
Darwin and Wallace put forward the argument that if species are descended from
other species, then it makes perfect sense that closely related species would be
located nearby – the similar species having descended from a common ancestor.
very different collections of plants and animals in regions of the same latitude with
similar climates and conditions, for example the:
–South America and Africa biogeographical regions have all the same major groups
of mammals but do not have similar species. For example, monkeys are arranged
into two main groups: Old World monkeys (OWM) and New World monkeys (NWM),
which are distinguished by the form of the nose. OWM have narrow noses with
downward-facing nostrils, as do apes and humans. NWN have broad noses with
outwardly directed nostrils (‘flat-nosed’). Some NWM species have prehensile tails
capable of supporting the entire body weight. No OWM has this ability.
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Chacma monkey (OWM)
Black-howler monkey (NWM)
–flightless birds are found in South America (rheas), Africa (ostriches) and Australia
(emus). All three are different species and being flightless must have originated from
their own ancestor, as a common flightless ancestor could not have migrated across
the oceans.
Ostrich
Emu
Rhea
–large indigenous mammals in the Australian region are all marsupials, e.g. Koala
bears and kangaroos, whereas almost all large mammals in the other southern
biogeographical regions (South America and Africa) are placental.
Koala bears
Kangaroo
Since similar environments can contain entirely different species groups, the
organisms living in these areas must have descended by modification from
ancestors that were different in each particular place.
the distribution of species on oceanic islands. This is particularly important in

biogeography and is considered to show strong evidence of descent by modification.
Darwin and Wallace both noticed that within an archipelago (a group or chain of
islands) it is typical that:
–species while similar to each other differ slightly on each island of the group.
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–island species are more closely related to species living on the nearest mainland,
despite different environments, than to species from other island groups.
oceanic islands = usually formed as the result of volcanic action and are often
geologically ‘young’
Mockingbird distribution
The distribution of Darwin’s mockingbird species of the Galapagos Islands is a

classic example of evidence for evolution from biogeography.
Position of the Galapagos
It was these little-known mockingbirds, not finches, which gave Charles Darwin his
ideas about evolution. On a 6 400 km trip along the South American coast (Chile)
Darwin had seen only three species of mockingbird. Yet, when he went from one
Galapagos island to another, separated by just 80 km of water, he found two quite
different species unique to each island. He also observed that while different to each
other these island species were closer in appearance to those on the nearest
mainland than anywhere else in the world.
Darwin hypothesized that the different species of Galapagos mockingbirds were

descended from individuals of the mainland species that had somehow reached the
islands sometime in the past. These mockingbirds adapted to the new conditions on
the oceanic islands and developed into new species, showing evolution.
The fact that the two species are different from island to island also shows that, after
dispersal, the presence of a barrier such as the ocean allowed the birds to adapt
differently to the environment on each island, and for them to evolve into new
species.
Mockingbird
the biogeography of fossils. Darwin noted that fossils of extinct species closely
resembled living species that occurred in the same region. Two examples from
South America are:
–the fossil ground sloth, Megatherium ‘giant beast’ and its closest living relative, the
two-toed tree sloth.
–the fossil armadillo ‘little armored one’ which show anatomical similarities with living
armadillo species in the same areas.
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The two examples above show clearly that the modern species replaced and
evolved from the fossil forms.
fossil sloth
live sloth
fossil armadillo
living armadillo
‘Wallace’s Line’, first identified by Russel Wallace during the late 1850s, is an
imaginary line that bisects the Malay archipelago into two parts, north-western
(Sumatra and Java) and south-eastern (New Guinea, Sulawesi and Timor).
Map to show position of Wallace’s line
Each part has different groups of living organisms, despite their similar climate and
geology. Wallace worked out that deep seaways, which had always existed,
prevented migration of species between the islands. Therefore, the two different
groups of organisms must have arisen by descent by modification from different
ancestors on each side of the line.
Note:
Due to plate tectonics, the earth’s crust is constantly changing as continental and
oceanic plates move. Mountains rise and fall and oceans form and disappear. These
changes have greatly affected the distribution of organisms. As some became
isolated from each other, they evolved into different species. An example of a large
land mass breaking-up is Gondwanaland that split into South America, Africa and
Australia.
Darwin observing a mocking bird
Learning activity 6
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Biogeography and evolution
Question 1
Devise a series of learning diagrams to show the five biogeographical patterns

observed by Darwin and Wallace. Apart from headings, do not use any words.[8]
Question 2
Darwin’s travels during the voyage of the Beagle allowed him to notice some
important patterns in the diversity and distribution of species in very diverse
geographic areas.
Read the following passage from his autobiography and answer the questions that
follow.
From September 1854 onwards I devoted all my time to arranging my huge pile of
notes, to observing, and experimenting, in relation to the transmutation (change) of
species. During the voyage of the Beagle I had been deeply impressed by
discovering in the Pampean formation great fossil animals covered with armour like
that of the existing armadillos; secondly, by the manner in which closely allied
animals replace one another in proceeding southwards over the continent; and
thirdly, by the South American character of most of the productions (organisms) of
the Galapagos archipelago, and more especially by the manner in which they differ
slightly on each island of the group; none of these islands appearing to be very
ancient in a geological sense. It was evident that such facts as these, as well as
many others, could be explained on the supposition (hypothesis) that species
gradually become modified; and the subject haunted me.
1.Mention the three key biogeographical observations Darwin made while on his
voyage that influenced his thoughts on evolution. Give examples of the relevant
organisms. (6)
2.What did these observations lead Darwin to suggest? (1)
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3.Why do you think the idea that ‘species gradually became modified’ haunted
Darwin? (2)
[9]
Question 3
Wallace noticed that in the Malay archipelago there was a complete change in the
kinds of birds and other animals inhabiting the islands of Bali and Lombok, which
were separated by a 32-kilometre strait. Can you explain the reason for the
difference? [3]
Total [20]
3. Evidence from genetics
Genetics is the science of heredity, which includes the study of genes and the
inheritance of variation and traits of living organisms. It deals with resemblances and
differences of related organisms which is why it is valuable in giving evidence of
evolution.
Evidence of evolution can be seen by studying and comparing chromosomal DNA

and mitochondrial DNA (mtDNA). You will have learnt about both chromosomal DNA
and mtDNA in the Genetics unit.
Not only does they show that all organisms have descended from a common
ancestor but also shows how closely organisms are related to each other.
The following information shows that all organisms must have originated and evolved
from a common ancestor and must be genetically related.
1.All organisms have descended from a common ancestor because:
all organisms have DNA and RNA.
there are many genes in all living organisms that are encoded to make identical
proteins, e.g. the enzymes used in cellular respiration, which are proteins.
2.Organisms are related to each other by varying degrees
The evidence of evolution shown by molecular biology goes even further. Scientists
can use the similarity of sequences of chromosomal DNA and mt DNA nucleotide to
work out how related species are.
The more sequences shared, the closer the relationship between two species and
the more recently they diverged from a common ancestor.
The fewer sequences shared, the more distant the relationship between two species,
and the further in the past the species diverged from a common ancestor.
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For example, in humans and chimpanzees, the protein molecule called cytochrome
c, which serves a vital function in respiration within the cells of all forms of life,
consists of the same 104 amino acids in exactly the same order. It differs, however,
from the cytochrome c of:
–rhesus monkeys by one amino acid
–horses by eleven additional amino acids
–tuna by 21 additional amino acids.
The similarity shows how recent common ancestry was between humans and
chimpanzees.
Thus, the evidence for evolution, which Darwin drew from biogeography,
palaeontology, homology and embryology, can be confirmed by molecular studies of
chromosomal DNA and mtDNA, i.e. genetics.
Learning activity 7
Genetics and evolution
Design learning diagrams to illustrate how genetics and molecular biology can show:
a.Evidence of a common ancestor for all organisms
b.How related organisms are
a.
b.
4. Comparative anatomy evidence
By comparing external and internal structures, scientists can find out how related two
organisms are. This is known as comparative anatomy and provides evidence of
evolution. The reason for this is that organisms with similar structures or
characteristics might have acquired these features from a common ancestor and
therefore are on the same evolutionary lineage. Such features are known
as homologies. The number of shared homologous features between any one
species and another indicates how recently those two species diverged from a
shared lineage.
Homologous structures must be similar in fundamental structure, position and

development. However, homologies can be superficially different, e.g. flippers of
whales and legs of a horse have the same basic structure but do not perform the
same function.
An example of a homology is the pentadactyl forelimb of vertebrates. The same

bones in the basic pentadactyl forelimb have been used in many ways and lead
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to divergent or adaptive radiation evolutionary paths – frogs (amphibians), birds
(aves), bats (mammals), people (mammals) and so on. All these animals shared a
common ancestor that had the same bones.
In Grade 11 you studied the basic plan of the mammalian forelimb as well as the
different ways it was adapted, e.g. for digging (mole), flying (bat), fast running
(horse) and climbing (monkey).
Analogous structures are structures that are similar in different organisms because
they evolved in a similar environment, rather than being inherited from a recent
common ancestor.
These structures usually serve the same or similar purposes. Therefore, comparative
anatomists cannot assume that two organisms are related to one another and have a
common evolutionary origin just because they have a similar structure such as a
wing.
For example, one cannot say bats and insects share a common ancestor because
they both have wings.
Analogous wings of a bat and an insect
A closer look at the structure of the wings shows that there is very little in common
between them besides their common function – one is made of bone, flesh and
feathers while the other is composed largely of non-living chitin.
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In other words, bats and insects with their analogous wing evolved their ability to fly
along two very separate evolutionary paths and not because they have a common
ancestor.
These similar structures are said to be the result of convergent evolution.
Learning activity 8
Molecular biology, DNA and evolution
Question 1
Fill in the missing words of the following summary showing the link between
evolution and genetics.
1.All organisms have a common ancestor as they all have:
1.1.____________________ and __________________________ molecules.
1.2.the same genetic _____________________ to make the same.
2.Degree of relatedness between organisms can be determined by working out the

number of:
[5]
Question 2
The following information shows the percentage of protein-producing genes that are
identical to those found in humans:
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Yeast – 45% identical
Fruit flies – 60% identical
Chickens – 90% identical
Rabbits – 95% identical
Chimpanzees – 98% identical
1.What biological theory could the preceding information support? (1)
2.What aspect of the theory does the given information suggest? (2)
3.What does the given information show about the relationship between the
organisms listed above? (3)
4.Suggest why fruit flies are excellent study subjects in the search to learn about
human genetics. (4)
[10]
Total [15]
5. Embryology
By studying the embryos of various organisms, e.g. vertebrates, one can see marked
similarities in structure during the early stages of the development.
In vertebrates it is quite difficult to tell the difference between the early embryos of a
fish, bird, pig or a human. This supports the idea that these organisms came from a
common ancestor.
These embryos all have:
a nerve cord that becomes the spinal cord surrounded by a series of vertebrae
forming the vertebral column
gill slits
a fish-like heart
a tail.
With further development of the embryo, these fish-like features are lost, and they
grow less similar, taking on the characteristics of the vertebrate group to which they
belong.
Embryos of various vertebrates
6. Vestigial organs
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Some organisms have structures or organs that seem to be stunted and have no
function: these are known as vestigial organs. They are often homologous to organs
that are useful in other species. Thus, vestigial structures can probably be viewed as
the most easily convincing pieces of evidence for evolution: organisms having
vestigial structures must have shared a common ancestry with organisms in which
the homologous structure is functional. Consider a species of fish that lives solely in
total darkness in caves and has rudimentary, stunted, non-functional eyes that
cannot detect light. Why possess such a useless structure? If this species was
created as it now is, and did not evolve from an ancestral species, ‘blind’ eyes are
hard to explain. Other examples of vestigial structures include:
the tailbone in humans, homologous to the functional tail of other primates. This
feature, called the coccyx has little apparent function in modern humans.
the appendix in humans, a narrow tube attached to the large intestine. In some plant-
eating mammals, the appendix is a functioning organ that helps to digest plant
material. In humans, however, the organ lacks this purpose and is considerably
reduced in size, serving only as a minor source of certain white blood cells that
guard against infection.
the rudiments of a pelvic girdle buried in the hindquarters of a dolphin. Why, when it
has no hind limbs?
Evolution – a scientific theory and not just a hypothesis
Difference between hypothesis and theory
To most people the words ‘hypothesis’ and ‘theory’ mean the same. However, a
scientific hypothesis is not the same as a scientific theory.
A scientific hypothesis is an idea or possible explanation about something observed

that suggests a question.
It takes the form of a statement. For example, ‘If there are warm nights after periods
of rain then frogs will sing’.
Notice the ‘If... then’ in the wording of the hypothesis, it is a useful and ‘safe’
way of writing a hypothesis.
Hypotheses can be supported or disproved with experimentation or more

observations, i.e. hypotheses are testable ideas. They come and go by the
thousands, but theories often remain to be tested and modified for decades or
centuries.
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A scientific theory is a general explanation of an important natural phenomenon with
a reliable body of evidence that has developed through extensive and repeated
observations and experiments to support it.
So, one can in fact say that a theory is an ‘accepted hypothesis’.
A theory will not become widely accepted unless its predictions:
can stand up to thorough and repeated testing.
are confirmed by more observations.
are confirmed by other independent peer review researchers.
have been published in peer-reviewed literature.
A theory remains valid only if every new piece of information supports it. If not, the
theory is disproved.
peer review researchers = experts in the same field who look for weaknesses and
errors and make an unbiased evaluation of the piece of research
What is the relationship between a hypothesis and a theory?
The diagram below shows the relationship between a hypothesis and a theory and
how a theory develops.
To show relationship between hypothesis and theory
Why is evolution a theory and not a hypothesis?
Evolution as a theory, which explains the history of life on earth, has been confirmed
through multiple lines of evidence – fossil record, biogeography, genetics, molecular
biology, homologies, etc.
In the beginning, evolution would have been regarded as a scientific hypothesis until
all the different pieces of evidence had been carefully looked at, discussed, written
about and thoroughly tested. After these processes evolution then became an
accepted theory.
Evolution is not a hypothesis
Beginning of conflict between religion and science with respect to evolution
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Before the theory of evolution was proposed, species were believed to be
unchanging. All forms of life were as the creator made them, and the world was
believed to have be created about 6 000 years ago.
However, in the 1800s the work of the geologist Lyell showed that the earth was in
fact very old. This, with Wallace and Darwin’s explanation of how evolution took
place by natural selection, challenged these beliefs, contradicting a literal
interpretation of creation in various religious texts.
The following ideas are worth noting:
Evolution is a well-established fact that is well supported by multiple lines of

evidence.
While Darwin’s ideas are correct, the mechanisms of evolution are only partly
understood, and are still being researched and added to by modern science.
Both science and religion are important to humans but in different ways.
For some the two are at war; for others they are not only reconcilable but also
complementary. Today many people feel that the theory of evolution can be
reconciled with the bible and other sacred texts where accounts of the origin and
development of life are interpreted symbolically, not literally. Many respected
scientists believe that evolution could be the creator’s way of planning the
development of living things.
–Science does not answer all questions. It deals with the material world. It
investigates the physical and natural aspects of life by using logical observations and
experiments to draw conclusions.
–Religion is concerned with strongly held beliefs, morals (ethics), attitudes that one
lives by, and spiritual, philosophical and ethical ‘why?’ questions. Religious books
are an ethical guide for humanity, not a scientific treatise.
Science and religion cannot be used to test each other; their goals, methods and
philosophies are far apart.
Science and religion can be complimentary rather than antagonistic.
Science is an ongoing process that is pursued by observation and experimentation.

This is not the focus of religion, which is open to moral, ethical and philosophical
interpretations.
Science does not claim to know everything. It explains how life developed through
evolution but is still far from explaining the great mystery of how life started, which
appears to happened only once and to have taken place very early in the history of
the earth. The theory of evolution explains how organisms developed into the wide
diversity of forms that we observe today.
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It is important to realise that free will is a characteristic of all human beings, and we
are in control of our destinies; where we seek guidance is up to us.
When discussing evolution we should adopt the following ideas and views:
Always have respect for the views of others.
Develop knowledge that will allow you to understand evolution and answer views
about it.
Insist on testability of ideas about evolution.
Have the honesty to recognise and acknowledge areas of ignorance, both personal
and those of science.
Distinguish the different goals of science and religion.
Be able to show how relevant and important evolution is today, e.g. antibiotic
resistance, new HIV strains, multiple-drug resistant TB.
1. Multiple choice
answer below.
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.
1.Convincing scientific evidence now indicates that:(a)evolution has occurred in the

past but no longer is occurring;(b) evolution is now occurring, but it did not occur in
the past;(c) evolution is occurring now;(d) evolution only occurs after mass
extinctions.
2.Darwin drew ideas for his theory from observations of organisms on:(a) the
Samoan Islands;(b) Manhattan Island;(c) the Hawaiian Islands;(d) the Galapagos
Islands.
3.Evidence that evolution occurs includes all of the following except:(a) acquired
characteristics;(b) similarities and differences in proteins and DNA sequences
between organisms;(c) the fossil record;(d) homologous structures among different
organisms.
4.The biodiversity on earth is a result of:(a) many species dying out;(b) evolution
from common ancestors;(c) transitional fossils being found; (d)Gondwanaland
splitting up.
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5.The forelimbs of most terrestrial vertebrates have five digits in each limb. This
comparative anatomy suggests that:(a) these organisms came from the sea;(b) all
these organisms could fly;(c) these organisms are related to one another and
probably shared a common ancestor;(d) these organisms arose before invertebrates.
6.The mechanism driving evolutionary changes remained unclear until the theory of
natural selection was discovered by:(a) Gregor Mendel and Charles Darwin;(b)
Charles Darwin alone;(c) Erasmus Darwin and Russel Wallace;(d) Charles Darwin
and Russel Wallace.
7.Multicellular organisms, such as fungi, plants and animals, have been found:(a) in
all geological layers;(b) only in ancient geological layers;(c) only in younger
geological layers;(d) only in pre-Cambrian rocks.
8.As species diverge from a common ancestor, they:(a) accumulate more

differences;(b) have fewer differences;(c) become larger;(d) are fewer in number.
9.Biogeographical evidence of evolution is based on:(a) transitional fossil forms;(b)

genetic differences;(c) the distribution of organisms in space;(d) groups of organism
having homologies.
10.The fossil record is somewhat biased and incomplete because:(a) most

organisms become fossils.(b) most fossils are of aquatic animals.(c) hard bodied
organisms are less likely to form fossils.(d) all of these options are correct.
11.When discussing evolution and religion which of the following ideas are correct:
(a) Evolution is not an established fact. (b) Science answers all questions. (c)
Science and religion cannot be used to test each other.(d) Science and religion can
be complimentary rather than antagonistic.
12.The following people played a role in the development of the theory of

evolution:(a) Charles Darwin and Gregor Mendel;(b) Gregor Mendel and Jean-
Baptiste Lamarck;(c) Russel Wallace and Charles Darwin;(d) all of them.
13.How do hypotheses differ from theories?(a) Theories are more comprehensive

(complete) than hypotheses.(b) Hypotheses are derived by experimentation; theories
are derived from observation.(c) Hypotheses are educated guesses, and theories
are tentative explanations.(d) Theories must be testable; hypotheses do not need to
be testable.
14.All organisms share common ancestors because they:(a) all have DNA
molecules.(b) all make proteins in the same way.(c) all contain proteins made of the
same 20 amino acids.(d) all three.
15.Genetics was completely unknown when Darwin put forward his theory, but it
explains the things Darwin observed with amazing accuracy. Genetics:(a) explains
how variation appears within species(b) explains how species fall into taxonomic
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groups(c) allows us to track the evolutionary history of any species by comparing its
DNA to those other species in the same clade (d) explains all three options.
[15]
2. Terms
Write down the correct term for each of the following statements in the space
provided.
Statement Term
1. The study of the distribution of organisms in space and time.
2. The most easily observable historical evidence for evolution.
3. An educated idea based upon observation.
4. The common term for descent by modification.
5. Branch of biology that deals with molecules.
6. The book containing the first convincing explanation of the mechanism

for evolution.
7. Molecule that contains the genetic code.
8. The imaginary line dividing the Malay archipelago into two different
ecological regions.
9. Flightless birds found in South America.
10. A group or chain of islands.
[10]
3. True and false
Decide if the statement is T (true) or F (false). Write T or F and in the space write the
incorrect and correct word/term.
Statement T/F Incorrect /

Correct term
1. Species sometimes reappear after they become extinct.
2. Biogeography shows us that new species only arise near
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very similar species.
3. Undisturbed sediment layers should show older species at

the top.
4. Science does not answer all questions. It only deals with the
spiritual world.
5. Evolution continues today.
6. Fossils show that there has been a decrease in the diversity

of families of species over time.
7. The amount of information about evolutionary history stored

in fats and proteins of living things is enormous.
8. All proteins in all organisms consist of some of 200 amino

acids.
9. Genetics analysis is less important in testing evolution than

comparative anatomy and fossils.
10. Evolution is a theory for which there is little evidence.
11. Lamarck thought that traits acquired during the lifetime

could not be inherited by the next generation.
12. Protein synthesis and their functions are very different in all
organisms.
13. On an archipelago (group of islands) species, while similar

to each other, differ slightly on each island of the group.
14. Fossils of extinct species are seldom found in the same

area as similar living species.
15. Erasmus Darwin proposed two things relating to evolution –

living organisms have a common ancestor and species
changed over time.
[15]
4. Mix and match
Match each description in Column B with a corresponding item in Column A, and

write your answer (letter) in the space provided.
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1. Jean-Baptiste Lamarck 1. A. Origin of diversity

____
2. natural selection 2. B. Species fixed by divine creation 6 000

____ years old
3. Principle of Population by 3. C. Zoonomia

Malthus ____
4. palaeontology 4. D. Inheritance of acquired characteristics

____
5. Archaeopteryx 5. E. ‘struggle for existence’

____
6. Erasmus Darwin 6. F. One of Darwin’s proofs of descent with

____ modification
7. molecular biology 7. G. Mechanism of evolution

____
8. evolution 8. H. Study of prehistoric life

____
9. pre-1700s idea of origin 9. I. Intermediate between reptiles (dinosaurs)

of species ____ and birds
10. biogeography 10. J. Can give an accurate measure of how

____ related organisms are
[10]
statement.
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Statement Ans Items
1.Extinction of organisms 1.part of the evolutionary process

is...
2.invisible in the fossil record
2.Fossil record shows 1.many kinds of extinct organisms were very

that... different in form from those now living
2.successions of organisms through timeshow

transition from one form to another
3.The Origin of Species 1.evidence for evolution
2.mechanism for evolution
4.Lamarck’s explanation of 1.change was by branching and was directed by

evolution nature
2.directed by the creatures themselves
5.Biogeographical patterns 1.colouration of animals for sexual selection

purposes
2.very different animals on different continents

at same latitudes and climates
6.Proof of a common 1.all organisms have DNA with the same four
ancestor base molecules
2.all organisms have the same 20 types of

amino acids
7.Scientific theory 1.once established does not need to be

subjected to repeated testing
2.is an untested, general explanation of an

important natural phenomenon
8.Homology 1.similar characteristics in two animals that are a

product of different evolutionary lines
2.product of a similar environment
9.Fossils found in recent 1.very similar to living species
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layers are... 2.less diverse than those found in earlier layers
10.Evidence in support of 1.species are dying out in large numbers

evolution
2.genetic studies and comparisons of DNA
sequences
[10]
Total [60]
4.2 Fundamental aspects of evolution
Macro-evolution
Macro-evolution is the change that occurs at or above the level of species, in

contrast with micro-evolution, which refers to smaller evolutionary changes (typically
described as changes in allele frequencies) within a species or population over long
periods of time. It includes the remarkable trends and transformations in evolution,
such as the origin of mammals and the radiation of flowering plants.
It is not easy to ‘see’ macro-evolutionary history; there are no first-hand accounts to

be read. Instead, history of life is reconstructed using multiple lines of evidence, such
as molecular sequencing data, geology, fossils and living organisms.
Two terms that are very useful to know and understand are phylogeny and
phylogenetics.
Phylogeny is the scientific study of evolutionary relationships among species.
Phylogenetics is the study of evolutionary relationships among groups of organisms

which have been discovered through the lines of evidence mentioned earlier.
Phylogeny can be represented in phylogenetic tree, where the trunk and stems are
lineages of ancestors, the branching points representing divergences between
lineages, and the tips of the branches living species (or extinct species that died
without descendants).
Example of a phylogenetic tree plan
What is the tree of life?
The tree of life is a metaphor describing the relationship of all life on earth in an
evolutionary context.
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What are some patterns that are repeated in the tree of life?
1. Stasis/equilibrium
Many lineages on the tree of life exhibit stasis/equilibrium, which just means that
they don't change much for a long time, as shown in the figure below.
In fact, some lineages have changed so little for such a long time that they are often
called living fossils. Coelacanths make up a fish lineage that branched off of the tree
near the base of the vertebrate clade. Until 1938, scientists thought that coelacanths
went extinct 80 million years ago. But in 1938, scientists discovered a living
coelacanth. Hence, the coelacanth lineage shows about 80 million years of stasis, it
has the same body form.
2. Lineage-splitting (or speciation)
Patterns of speciation and times of speciation can be identified by constructing and

examining a phylogeny, i.e. the evolutionary history of a species (or group),
especially in reference to lines of descent and relationships among other groups of
organisms. The phylogeny might show cladogenesis or anagenesis.
Cladogenesis is an evolutionary splitting event where a parent species splits into

two distinct species, forming a clade.
A clade is a life-form group consisting of a common ancestor and all its

descendants—representing a single ‘branch’ on the ‘tree of life’.
In the following diagram the pattern seen by a species formed by cladogenesis (C) is
that they live at the same time as other species (D) that came from the common
ancestor (B).
Cladogenesis
In anagenesis the ancestral species gradually accumulates changes, and

eventually, when enough is accumulated, the species is sufficiently distinct and
different enough from its original starting form that it can be labelled as a new form -
a new species. Note that here the lineage in a phylogenetic tree does not separate.
Anagenesis is not often shown in the phylogenies that you will be looking at.
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Anagenesis and cladogenesis
Palaeontologists see the role of cladogenesis as more important in evolution to that

of anagenesis. Anagenetic trends are often associated with micro-evolutionary
trends, and cladogenetic ones with macro-evolutionary trends.
3. Adaptive radiation
Adaptive radiation is the burst of divergence from a single lineage to give rise to
many new species from a single ancestor.
This pattern of macro-evolution, a form of cladogenesis, occurs to fill up new

ecological niches as in the case of the finches on the Galapagos Islands. Over time,
the organisms that have evolved from the common ancestor adapt and change even
further.
Adaptive radiation
Examples of adaptive radiation
The fossil record contains many examples of adaptive radiation.
Some 315 million years ago, the reptiles became truly terrestrial (land-living) as they
no longer relied on returning to water for reproduction (as do all Amphibian (frog)
species). The development of the amniotic egg - an egg that retains its own water
supply and can survive on land – allowed reptiles to breed on land.
Once on land they diversified rapidly into the various new terrestrial environmental
niches.
Amniotic egg
Later a similar, even more rapid burst of diversification gave rise to the birds.
After the dinosaurs became extinct, there was an explosion of mammalian evolution
from 65 to 50 mya with many different species appearing at the same time in the
fossil record. This was as a result of climatic change as well as the extinction of the
dinosaurs. Suddenly there were many empty niches that could be filled by the
adaptable early mammals.
Mammalian adaptive radiation
4. Extinction
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Extinction is extremely important in the history of life. It can be a frequent or rare
event within a lineage, or it can occur simultaneously across many lineages (mass
extinction). Every lineage has some chance of becoming extinct. Over 99% of the
species that have ever lived on earth have gone extinct. In the diagram below, a
mass extinction cuts short the lifetimes of many species and only three survive.
What are some trends that appear in macro-evolution?
Trends that appear in the tree of life include the following:
The major trend has been towards increased complexity, e.g. prokaryotes (no
nucleus) to eukaryotes (have a nucleus), single-celled protists to multi-cellular
organisms, primitive societies to the emergence of human societies and the origin of
language.
Increasing body size, e.g. in horses (see page 202) and increases in body size and
cranial capacity during hominin evolution 850cc→13 30cc in about 2 million years
(see page 267).
Evolving from marine habitats, then to terrestrial habitats, before evolving the ability
to fly.
Rate of change in evolution – gradualism and punctuated equilibrium
Palaeontologists have observed examples of both gradualism and punctuated

equilibrium in the fossil record. Both happen, but scientists are trying to determine
which pace is more typical of evolution and how each sort of evolutionary change
happens.
Gradualism
This hypothesis puts forward that species evolve gradually by small changes over
long periods of time. Darwin put forward this suggestion in his book Origin of
Species.
A well-known example of gradualism is the evolution of humans. Instead of fast

advancements and spontaneous spurts of rapid evolution humans followed a ‘linear’
pattern of evolution - a pattern of gradual evolution. Although the fossil record is still
incomplete, the slow gradual changes in the evolution of Homo sapiens are well
documented.
The following diagram illustrated Darwin’s concept of gradualism.
Diagram to show slow, gradual change in a butterfly species

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Punctuated equilibrium
Stephen Jay Gould (1941-2002) was one of the most influential evolutionary
biologists of the 20th century and perhaps the best known since Charles Darwin. He
made scientists rethink well-established ideas about the patterns, pace and
processes of evolution.
What is punctuated equilibrium?
Punctuated equilibrium refers to the speed at which evolution takes place.

According to the theory Gould formulated, punctuated equilibrium, evolution is not
gradual as proposed by Darwin.
By studying the fossil record he found long periods of time, sometimes millions of
years, where species did not change or changed very little (known as equilibrium).
This alternated with (was punctuated by) short periods of time where rapid changes
occurred through natural selection.
As a result new species were formed in a short period of time (rapidly), relative to the
long periods of little or no change
This is supported by the absence of transitional fossils (often termed ‘missing links’)
indicating the period of rapid change.
It means that most phenotypic modifications occur when species first branch off from
the parent species and then change little after that – as long as the environment
stays stable. This can be seen in the diagram below.
Gould predicted that events such as volcanic eruptions and meteor impacts created
great environmental changes. These sped up evolution because, for species to
survive, they would need to adapt quickly to the new environment. Those that did not
adapt became extinct. This theory is becoming accepted by more and more
scientists.
Punctuated equilibrium
As an example, a study of fossil snails at Lake Turkana (Kenya) demonstrated that

the snails showed no change for very long periods followed by occasional sudden
change. These changes were associated with changes in lake levels due to climate
change.
Fossil snails from Lake Turkana
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Evolution by natural selection
Evolution occurs through different mechanisms. Darwin’s idea of evolution by natural

selection is one of the basic mechanisms of evolution.
Darwin made four observations that led him to formulate his observations about a
mechanism of evolution. The ideas are simple but they explain that overtime there
can be change and adaptation within species.
Darwin’s four observations
1.More offspring are produced than are required
Darwin and fellow scientists knew that populations usually produced more offspring
than the environment could support, yet populations generally remained relatively
stable in size over the long term.
Natural variation
Natural variation, e.g. colour, size of beaks, muscular strength, etc., exists among
individuals of a population, i.e. no two individuals are exactly alike.
While in Darwin’s era, he and others could see variation they did not know the
reason for it. The reason, we now know, is that every individual possesses a different
combination of genes.
Natural variation in a population of beetles
3.A change in the environment leads to differential reproduction
The question that needed an answer was - if populations remained relatively stable
which individuals were most likely to survive? Darwin reasoned that the better
adapted individuals would be likely to survive to reproduce while the less adapted
would most likely die or fail to reproduce. This became known as differential
reproduction, or ‘survival of the fittest’. The less-adapted individuals were
eliminated and could become extinct. In other words of the large number of off-
spring, only a few survive.
You might have heard of the phrase ‘survival of the fittest’. You obviously realise
that ‘fittest’ means best adapted – and not strongest.
4.Characteristics (traits) were heritable
Darwin observed and noted that characteristics were heritable, i.e. they passed from
parents to offspring.
Learning activity 1
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Darwin’s four important observations
Devise a clear simple learning diagram to show the essence of the four observations
that helped Darwin formulate his theory of natural selection.
How did Darwin explain natural selection?
This section is important!
Basic to the understanding of natural selection is the fact that natural

selection only operates on variation in inherited characteristics. If all individuals of a
population were genetically identical, there would be no natural selection.
Natural selection is a process by which nature (the environment) selects for survival
those individuals that are best adapted to environmental conditions and, as a
result, will produce the most offspring.
Learn this very important definition!
Natural selection thus provides a mechanism for evolution, which can adapt
species to the environment and ultimately may lead to the origin of new species.
Species that do not adapt become extinct.
How does natural selection occur?
Combining his four observations, Darwin explained how evolution could occur by
natural selection. The diagram below is an illustrated description of his explanation.
As you will see it is relatively simple.
1.Organisms produce a large number of offspring
2.There is a great deal of variation among the offspring. In this example

some caterpillars are hairy other are not. Natural selection always acts on
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variation.
3.When there is a change in the environmental conditions (new climatic

conditions, disease, new predator) or there is competition there is a struggle
for survival. In this case the environmental pressure is the arrival of a new
predator that likes to eat non-hairy caterpillars!
4.Some off-spring will have a favourable trait that allows them to adapt to
the changed environment. They are therefore more likely to survive. The
favourable trait hairiness, gives hairy individuals a greater chance of
surviving.
5.Whilst organisms without the favourable trait are less able to adapt and so
will die.
6.The organisms that survive will reproduce and thus pass on the favourable
trait to their off-spring. The next generation will therefore have a higher
proportion of individuals with the favourable trait. Natural selection can act
only on heritable traits, traits that are passed from organisms to their
offspring during reproduction.
7.If this process continues, eventually all the individuals in the population
will have the desirable trait and in this case will be hairy, i.e. evolution by
natural selection will have taken place.
8.Eventually, by accumulating this and other such small changes in a

population, a new species might arise.
Now, what might happen if a new bird species that liked to eat hairy caterpillars
migrated into the area? Discuss this in class. Are you beginning to get the idea of
natural selection?
While natural selection is correct, it is not the only mechanism of evolution.
To sum up:
Life forms have evolved from previous life forms by natural selection. Most species
are unable to survive in a new environment and become extinct, but a few species
may successfully adapt to a new environment and ultimately may lead to the origin of
new species.
Natural selection thus provides a mechanism for evolution.
Is natural selection a random process?
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Natural selection is definitely not random as the organisms that are selected for
survival are those that are better adapted to the environment. However, the ways by
which variations arise, e.g. by mutations and recombination of genes during sexual
reproduction, are definitely random.
Does natural selection result in perfection?
Natural selection is not all-powerful; it does not produce perfection; no population or

organism is perfectly adapted. Think of us humans: are we perfectly adapted to our
environment?
It is more accurate to think of natural selection as a process rather than as a guiding

hand. It is mechanical, has no goals, and is not trying to cause development or a
balanced ecosystem.
Learning activity 2
Natural selection
1.Darwin observed pigeon breeders selecting particular novel characteristics to

breed new strains of pigeons.
This influenced his thinking about the mechanism of evolution. What was it, he
suggested, that selected new characteristics during evolution? (1)
2.What were Darwin’s four key observations that helped him develop his theory of
natural selection? (4)
3.What type of characteristics does nature select during evolution? (1)
4.In nature, there is always a struggle for existence because of competition,

predation and adverse climatic conditions. Suggest a collective term for these three
factors. (1)
5.Why is the concept of ‘natural selection’ so important? (1)
6.Why is natural selection not a random process? (2)
7.In the box below design a clear simple flow chart or mind map that will imprint on
your mind the process of natural selection. (5)
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Total [15]
It is simple, isn’t it? Remember, ‘natural selection’ will come up in some form or
another in your final examination so you must understand it and be able to explain it.
Natural selection only operates on variation in inherited characteristics
If all individuals of a population were genetically identical, there would be no natural

selection. There must be some genetic variation within a population, which can
influence the nature of the offspring, so that environmental conditions can select the
best adapted individuals.
Darwin’s greatest difficulty was a lack of understanding inheritance. Gregor Mendel

did publish his ideas in Darwin’s lifetime, but Darwin was unaware of them.
What causes genetic variation?
Variation of the genetic characteristics of eggs and sperm can be caused by:
Germ-line point mutations, which are the main source of genetic variation and
have a strong influence on evolution.
germ-line = in the eggs or sperm
Duplication of genes or swapping their positions within chromosomes.
Whole chromosomes may be deleted or duplicated, and even the entire

chromosomal compliment can multiply in a process called polyploidy. Polyploidy is
very important in the evolution of new species of plants. See page 228.
Sexual reproduction results in the formation of a new combination of alleles by the

processes of meiosis, chance fertilisation and random mating. See page 175.
As a result of these processes a variety of genotypes (genotypic combinations)

are formed in the offspring.
It is important to realise that it is only ‘new’ genetic characteristics in the eggs or

sperm that will be inherited by the offspring. Any genetic changes in the somatic
(body) cells cannot be inherited by the offspring.
Why do offspring differ from their parents?
Phenotypic changes in the offspring are due to both:
genetic variation (new combinations of alleles), and
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effect of environmental factors such as food, temperature, pH, sunlight, etc., on
the expression of the genotype. For example, even if the genotype carries genes for
the production of large muscles, the animal will not develop big muscles if there is
too little protein food available for the muscles to develop.
In this way a variety of phenotypes can be formed.
Why are only some offspring selected for survival?
Selective forces (environmental pressures) such as competition, predation,

climatic factors, disease and parasitism will favour some phenotypes more than
others, which results in differential reproduction.
Individuals with favourable phenotypic characteristics are selected. Being

better suited to the environment they will be more likely to survive and reproduce
successfully, so the proportion of their genes in the next generation will increase.
The individuals with unfavourable phenotypic variations will be less likely to

reproduce successfully, leaving few offspring with the unfavourable characteristics.
What is the result of natural selection?
A new favourable genotype thus becomes more frequent in the population.
If the genetic variation spreads throughout the whole population it is possible that
a new species may be formed.
An offspring with a favourable phenotypic change
Learning activity 3
Genetic process in evolution
After carefully studying the preceding information, fill in the missing facts in the
diagram below. [23]
A. Sources of variation in genotype
1.________________ mutations are the _____________ source.
2.Genes can be ________________ or change their positions on the chromosomes.
3.Chromosomal compliment can be multiplied in a process called

_______________________.
4.New combinations of genes form during ___________________reproduction. This

is due to:
a) shuffling of genetic material during ___________________________as a result
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of_________________________________________ of homologous chromosomes
and __________________________.
b) recombination during ___________________.
B. New____________________
C. Differential reporduction
Explanation of an example of natural selection: Peppered moth
The peppered moth (Biston betularia) provides a very good example of natural
selection.
Moth – pre-industrial revolution in England
The common colour of peppered moths was originally light, and this colour type
represented the predominant form in England prior to the beginning of the industrial
revolution. The moth’s light grey colour closely matched the lichen-covered trees in
their environment. Lichens are a slow growing life form that you can find on the bark
of many trees and in decomposing wood.
There was also a genetic colour variant in the moth population that resulted in some
very dark-coloured moths but these dark-coloured moths were relatively rare. Their
numbers remained low because when they landed on the light grey lichen-covered
tress, these moths were easy targets for predators.
Moth – after the start of industry
Early coal-based industry was extremely dirty. Around large cities, everything was
essentially covered in soot. This high level of pollution killed the light grey lichens on
trees and the bark became much darker in appearance.
When the light-coloured peppered moths landed on the same trees they had always
landed on, they were extremely visible against the dark bark, and easy targets for
predators. In this environment, the dark-coloured moth variant more closely matched
to colour of the trees and was now harder for predators to spot.
Over generations, the polluted environment continued to favour darker moths, and
they progressively became more common. By the late 19th century, 98% of the
moths near cities were black.
Dark moth – in era of modern, cleaner air
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Modern air pollution controls have cleaned up the environment compared to the early
days of the industrial revolution. A cleaner environment has allowed the lichens to
grown back, and the trees have returned to being lighter in colour. Now, natural
selection favours lighter moth varieties so they have become the most common, and
the dark-coloured variant is again rare.
Photograph showing light and dark moths on lichen covered bark
Other mechanisms of evolution
Natural selection is not the only mechanism of evolution. Other mechanisms

include polyploidy, gene flow and genetic drift. Although not specified in the
syllabus they need to be mentioned.
1. Polyploidy
Polyploidy is the doubling or even trebling of the two basic sets of
chromosomes. Often this also involves hybridisation between two species, and
when this happens, the offspring have a unique genetic composition and cannot
mate with either of their parental species. They ‘instantly’ thus become a new
species.
Polyploidy is rare in animals (goldfish and salmon) but it is immensely important in

the evolution of new species of plants. Wheat, for example, after millennia of
hybridisation and modification, has strains that are diploid, tetraploid, and hexaploid
(six sets of chromosomes), e. g. bread wheat.
Bread wheat (6n) arose by two separate events of hybridisation causing

polyploidy. See below.
2. Gene flow
Gene flow, another important source of genetic variation, is the movement of

genes between populations. This may happen through the migration of organisms or
the movement of gametes (such as pollen blown to a new location).
It is especially important in the sea, where larvae are widely dispersed by currents.
Gene flow
3. Genetic drift
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Genetic drift is a process that produces random changes in the frequency of
characteristics in a population.
Genetic drift results from the role that chance plays in whether a given trait will be
passed on to the next generation. It is important in small populations because
chance plays a greater role than natural selection in determining which individuals
reproduce and pass on their genes.
Genetic drift
Learning activity 4
Natural selection
1.How would Darwin have explained the fact that over the years the necks of giraffes
have been getting longer? How would Lamarck have explained it? (4)
2.The following sentences describe a process but the steps are out of order. In the
space provided write down the numbers to indicate the proper sequence of the
process and then name the biological process. (2)
1 Those offspring with differences that adapt them better to the environment will be
more likely to survive and reproduce.
2 Over time, this process gradually leads to entirely new types of life.
3 This means that more offspring in the next generation will have the helpful
difference.
4 This process is responsible for the many diverse life forms in the world today.
5 Offspring differ from their parents in minor random ways.
6 These differences accumulate and make populations change.
Sequence Name of process
[6]
Offspring differ from their parents in minor ways
3.Explain each of the following:
3.1A population of organisms that can reproduce sexually can often become adapted
to changes in the environment quicker than one that can only reproduce
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asexually. This is an important question: to answer it correctly you might need to
refer back to asexual and sexual reproduction. (6)
3.2Evolution does not stop once organisms have become well adapted to their
environment. (3)
[9]
4.Comment on the following statement.
We can see that variation, selection and time combine to stimulate the evolutionary
process.’[6]
Total [21]
Artificial selection
For thousands of years, farmers and breeders have used the variation in wild and
cultivated organisms to develop their crops and to create new breeds of livestock by
what is termed artificial selection.
Artificial selection is the process of selecting and breeding organisms with

desirable characteristics to produce offspring with those characteristics that will be
of some use to humans, e.g. horticulture, agriculture, transport, companionship and
leisure. Artificial selection mimics natural selection.
The selection process is simple; only those organisms with the desired trait are
allowed to reproduce.
Artificial selection, guided by humans and based on an understanding of genetics

and reproduction, is an artificial version of natural selection and evolution, which is
directed by nature.
What are the differences between artificial and natural selection?
Artificial selection Natural selection
Process occurs artificially via human naturally via environmental selective

… choice agents
Driven by man nature
Rate of change fast slow
Amount of less variation much variation

variation
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Consequence improved crops and adaptation to environment
livestock
What is the importance of artificial selection?
The importance of artificial selection is that over time it has enabled farmers and
breeders to:
domesticate wild plants (into uniform and predictable plants, e.g. wheat, maize and
rice) and animals (for higher milk, meat and wool production, e.g. cattle and sheep).
produce organisms that are resistant to pests and diseases.
improve the quality and yield of crops, e.g. there has been an approximate 50%
improvement in the major cereal crop yield since 1930.
produce new strains of crops, e.g. ‘new’ vegetables such as broccoli and Brussels
sprouts.
produce new hybrid crops, often called high-yielding varieties (HYVs), to meet the
ever increasing demands of human population. The HYV crops such as rice, maize
and wheat have an increased growth rate with higher yields.
However, HYV crops usually need extra care in the form of disease control, more
fertilizer and regular irrigation.
adapt old crops to enable them to grow in inhospitable climates or areas, e.g. where
there are environmental pressures such as salinity, extreme temperature or
drought. This will become more important as the effects of climate change are felt as
a result of global warming.
develop special breeds for particular purposes, e.g. dogs that herd sheep.
enhance the nutritional value and flavour of fruits and vegetables.
develop characteristics that are useful for storage, shipping and processing of foods.
Learning activity 5
Importance of artificial selection
Design a learning diagram without any words to show why artificial selection is
important.
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What is inbreeding and outbreeding?
Inbreeding is the mating of closely related individuals.
An extreme example is self-fertilization, e.g. wheat species.
A more common example is the crossing of offspring of the same parents, e.g. highly
pedigreed dogs.
The function of inbreeding is to select and continue particular characteristics.

However, it often leads to loss of vigour and poor survival as the offspring can
become homozygous for a higher proportion of undesirable recessive genes.
Outbreeding is the mating of individuals not closely related, e.g. mongrel dogs arise
in this way.
The resultant offspring of outbreeding are tougher and more fertile with a greater
chance of survival. The reason for this is that the offspring are probably
heterozygous with undesirable recessive alleles being masked by normal dominant
alleles.
Artificial selection in a domesticated animal, e.g. Canis familiaris
The different varieties of the dog, Canis familiaris, are a striking example of artificial
selection. The gene pool of dogs, 78 chromosomes (39 pairs), has a large amount of
hidden genetic variability, which can be expressed under selective forces.
gene pool = the total of all alleles of genes carried by all individuals in an
interbreeding population
The Grey wolf, Canis lupus, around 14 000 years ago, is thought to have been
ancestral to the dog species. From the ancestral species five ancient breeds
developed and each gave rise to a large number of distinct breeds of dogs.
When wolves were first domesticated, humans probably subconsciously bred wolves
that retained immature characteristics such as tameness, playfulness, subservience
and being easy to work with. Retention of immature characteristics in adults is known
as neoteny.
A wolf before puberty is friendly, co-operative and generally nice towards people
– the characteristics one would want in a pet.
Selective breeding over the centuries has produced the enormous variation seen in
today’s dog populations: more than 350 breeds. Different characteristics were
selected to produce dogs for specific purposes, e.g. for hunting, guarding.
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It is interesting to note that the different dog breeds show more behavioural and
phenotypic variation than any other species of land mammal.
Learning activity 6
Selective breeding of a domesticated animal
1.Which dog-like animal is thought to have been the ancestral dog species? (1)
2.What genetic feature of the ancestral dog enabled the breeding of such an
enormous number and variety of dogs? (1)
3.As with other animals produced by artificial selection, all dogs are potentially
interfertile. What does ‘interfertile’ mean? Why do you think dogs are ‘potentially’
interfertile? (2)
4.Dog breeders sometimes select neotenic (juvenile) characteristics. The young wolf
would have had these characteristics. Suggest characteristics found in adult dogs
that you consider be neotenic.
4.1structural characteristics (3)
4.2behavioural characteristics (3)
The concept of neoteny explains how our pet dogs are so much more fun to own
than wolves.
Total [10]
Artificial selection in crop plants
Of the approximate 75 000 species of edible plants 7 000 are used for food by
humans. Ninety percent of the world’s food comes from only 15 species with cereals
(wheat, maize and rice) making up two thirds of this amount. Today, all our principal
food crops come from domesticated varieties.
Domestication of wild plants has resulted in great phenotypic changes (and altered
genotypes) and the development of new varieties. All of these domesticated plants
are dependent on humans to preserve them. They are called cultigens to show their
dependence on cultivation. The practice of domestication is estimated to date back
9 000 to 11 000 years.
wild plants = plants that grow in nature without the aid of humans
What artificial selection methods are used in plant breeding?
There are two methods – classical and modern.
Classical plant breeding uses deliberate interbreeding (crossing) of closely or

distantly related individuals of a species to produce new crop varieties with desirable
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characteristics. For example, a mildew-resistant pea may be crossed with a high-
yielding but susceptible pea, the purpose of the cross being to introduce mildew
resistance without losing the high-yield characteristics.
Modern plant breeding, which includes:
–genetic engineering, which uses molecular techniques to:
➢select and transfer desirable characteristics from one plant to another, or
➢to change the genetic material to produce more desirable characteristics.
–Mutagenesis, which is the production, by chemicals or radiation, of mutants that

may have desirable characteristics.
–embryo rescue is the rescue of embryos from seeds of valuable plants, e.g. the
seeds of some popular orchids do not have enough food reserves which results in
too few seedlings being produced. The embryos, after being ‘rescued’ from the
seeds, are placed in a growing medium which ensures they will develop into
seedlings.
–polyploidy is the doubling or trebling the number of chromosome pairs in cells.

This can be induced by chemicals and has been important in generating new
varieties and even species, e.g. bread wheat.
Artificial selection in crops by the domestication of maize (corn, Zea mays)
About 10 000 years ago, early native Americans were able to change teosinte (Zea
mays ssp. parviglumis), a wild grass into maize – the largest grain crop in the world.
This transformation was not only the product of skilful breeding through artificial
selection, but also as a result of the remarkable genetic variation found in the
teosinte.
How did domestication occur?
Over the last thousand years farmers selected and planted seed from those teosinte
plants with beneficial characteristics, while eliminating seed from those plants with
undesirable features.
As a result, alleles of those genes controlling desirable characteristics increased in

frequency within the population, while less desirable alleles decreased.
Eventually all seed produced from the favoured plants produced plants with the
desirable characteristics.
What phenotypic characteristics were selected?
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To achieve this dramatic transformation from teosinte, a multi-stemmed wild grass,
into modern, upright Zea mays, many of the less common characteristics of teosinte
had to be selected.
Maize plant
Notice the multiple male tassels of the teosinte but only one of modern maize, and
the difference in ear structure.
Some characteristics that were selected
The following were some of the characteristics selected during maize domestication.
Reduced covering of kernel (seed)
In most teosinte plants the kernel is protected and surrounded by a hard outer
covering (glume).
In a few teosinte plants there was a trait that caused the covering to be much
reduced leaving the kernels exposed. This trait was selected and is found in modern
maize.
Such kernels would have been easier to chew and digest by humans.
Retention of kernels on the cob
The kernels of most teosinte individuals break off (shatter) from the cob. However,
some individuals retained the kernel on the cob, as found in all modern, major maize
varieties. These individuals were selected for breeding.
Erect habit with a single stalk
A teosinte plant has many side branches, each with a male tassel, whereas the
modern maize has a single stalk with only one male tassel. The upright trait,
probably a genetic mutant that prevented formation of side branches in a teosinte
individual, was selected for breeding. The upright habit concentrates energy
resources into a single stalk, resulting in larger ears that provided more food and
were easier to harvest.
Larger ear structure
Wild teosinte produces only tiny ears, a spike with a thickened axis, hidden in
clusters in the leaf axils with 6 to 12 kernels. Individuals with larger ears were
consistently selected with the result that modern maize has a cob (axis) consisting of
as many as 20 rows or more of kernels. The size of the ear has increased from 2 cm
to 30 cm during domestication.
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Teosinte and maize ears
In fact, teosinte is so unlike maize in the structure of its ear that 19th century
botanists failed to recognise the close relationship between these plants.
Something extra it is necessary to maintain biodiversity of wild plants and ancient

farm breeds
It is extremely important to keep as much genetic diversity of wild plants and ancient
farm breeds as possible. If genetic diversity is not maintained:
one unmangeable disease or insect pest could wipe out an entire crop or live-stock
species, temporarily or permanently. For example:
–in 1970, leaf-fungus destroyed about 15% of the USA maize crop. The industry was
saved by genetic material from wild maize plants, which had a blight–resistance trait.
–in the 1800s, an aphid attack nearly destroyed the European grape industry. It was
saved by the rootstock of North American wild grapes, whose natural resistance to
aphids continues today to protect grapes.
climate change will bring changes to agriculture. Farmers will need to breed new
crop varieties from wild plants, which will be productive under the new conditions.
Learning activity 7
Artificial selection in plants
Question 1
1.What is the main consequence of natural selection? (1)
2.What is the main methodological difference between artificial and natural

selection? (1)
3.The following statements (A to E) relate to the value of plant breeding. Arrange the
letters in the correct order of importance.
A.Better able to cope with stresses such as drought
B.Best way of securing food for us and our children
C.Raw material for breeding new crop varieties
D.Basis for more productive and hardy organisms
E.Genetic resources of plants

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(5) [7]
Question 2
As shown below, farmers have cultivated five common vegetable crops from the wild
mustard, Brassica oleracea, by artificially selecting for certain characteristics. The
vegetables are cabbage, Brussels sprouts, broccoli, Kohlrabi and kale. This is
evolution through artificial selection.
Wild mustard and derivatives
By looking at the above drawing of the wild mustard and each vegetable, answer the
questions that follow.
1.Name the vegetable that arose from:
1.1suppression (failure to develop) of internode length
1.2development of lateral meristems
1.3suppression of flower development (3)
2.Name the trait of the parental plant that was selected to produce:
2.1Kale
2.2Brussels sprouts (2)
[5]
Do you often eat these veggies? You should: they contain valuable anti-cancer
chemicals.
Question 3
Read the text below and answer the questions that follow.
Biodiversity losses threaten future food supplies
Widespread losses of plant species and varieties are eroding the foundations of
agricultural productivity and threatening other plant-based products used by billions
of people worldwide.
‘Plants provide us with irreplaceable resources,’ said John Tuxill, author of Nature’s
Cornucopia: Our Stake in Plant Diversity. ‘The genetic diversity of cultivated plants is
essential to breeding more productive and disease-resistant crop varieties. But with
changes in agriculture, that diversity is slipping away.’ In China, for example, farmers
were growing an estimated 10 000 wheat varieties in 1949, but this number had
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dropped to 1 000 by the 1970s. In Mexico, farmers today are raising only 20 percent
of the maize varieties they cultivated in the 1930s.
‘Biotechnology is no solution to this loss of genetic diversity,’ said Tuxill. ‘We are
increasingly skilful at moving genes around, but only nature can create them. If a
plant bearing a unique genetic trait disappears, there is no way to get it back.’
‘It is not just obscure or seemingly unimportant plants that are trouble,’ sid Tuxill.
‘Those that we rely upon most heavily are declining too. Some two thirds of all rare
and endangered plants in the United States are close relatives of cultivated species.
Crop breeders often turn to wild relatives of crops for key characterstics, like disease
resistance, when they cannot find those characteristics in cultivated varieties.’
Part of a report of a new study by the Worldwath Institute, a Washington-based

research organisation
1.According to this article:
1.1Why do we need to retain the genetic diversity of our cultivated plants? (2)
1.2Why can biotechnology usually not help replace those genes lost when a species
disappears? (1)
2.Mention two examples that show genetic diversity of cultivated plants is

decreasing. (2)
3.What is probably the most important characteristic that breeders look for in wild
plants? (1)
[6]
Question 4
Read the text below and answer the question that follows.
Corporations like Monsanto have developed genetically modified potato seeds that
contain an exotic gene from a soil bacterium that is resistant to harmful insects like
the Colorado potato beetle. The biggest problem for potato farmers worldwide,
however, is not beetles but a fungal disease called late blight.
Suggest why you think global agricultural research institutions are turning to
traditional farmers high in the Andes mountains of Peru, Ecuador and Bolivia and not
to Monsanto’s laboratories to counteract late blight?
[2]
Total [20]
Learning activity 8
Short questions
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1. Multiple choice
answer below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
1.Adaptation is the result of: (a) heredity; (b) differential reproduction; (c) variation;
(d) a, b and c.
2.An example(s) of natural selection that provides evidence of evolution: (a)

antibiotic resistance; (b) domestication; (c) modern maize; (d) all three.
3.Evolution begins with: (a) alterations in the genetic message; (b) excess population
growth; (c) adaptation to environment; (d) migration.
4.Cause of genetic variation: (a) sexual reproduction; (b) meiosis; (c) mutation; (d) all
three.
5.‘Survival of the fittest’ means the individuals are most likely to: (a) be the strongest;
(b) be the biggest; (c) reproduce successfully and pass on their good qualities; (d) all
three.
6.In artificial selection, humans choose which animal or plant they wants to breed so
that: (a) the offspring remain the same as the parent; (b) any change is a chance
occurrence; (c) evolution of that species will not take place; (d) a particular trait is
passed on to the offspring.
7.Which of the following characteristics was not selected when artificially

breeding Zea mays (maize)? (a) naked seeds, i.e. outside of a glume (case); (b)
non-shattering seeds; (c) numerous side branches with male flowers; (d) a single
stalk.
8.The process of classical breeding entails: (a) eliminating seed from plants with
desirable features. (b) selecting and planting seed from plants with beneficial
characteristics. (c) using plants with little genetic variation. (d) breeding over only a
few generations.
9.Which is not true as to why plant breeders use artificial selection today? It can:
(a) produce new variations that can grow in inhospitable areas, e.g. semi-desert
areas. (b) improve the dietary value and taste of vegetable and fruit. (c) develop
characteristics that are useful for storage and transporting. (d) make conserving the
wild varieties unnecessary.
10.The process by which a population becomes better suited to its environment is

known as: (a) accommodation; (b) adaptation; (c) variation; (d) evolution.
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11.The major idea that Darwin presented in his book The Origin of Species was that:
(a) species change over time and never compete with each other. (b) species
change over time by natural selection. (c) species may change in small ways but
cannot give rise to new species. (d) animals change, but plants remain the same
over time.
12.Natural selection is the process by which: (a) the age of selected fossils is
calculated; (b) organisms with characteristics well suited to their environment survive
and reproduce more successfully than organisms less suited to the same
environment; (c) acquired characteristics are passed on from one generation to the
next; (d) all three.
13.Natural selection could not occur without: (a) genetic variation in species; (b)
stable environments; (c) competition for unlimited resources; (d) gradual warming of
the earth.
14.Scarcity of resources and a growing population are most likely to result in: (a)
decreased homology; (b) increased genetic variation; (c) increased competition; (d)
convergent evolution.
15.Artificial selection has been used by humans to: (a) speed up the process of
evolution; (b) slow down the process of evolution; (c) stop evolution in domestic
animals; (d) none of these.
16.It has become very important to develop ‘gene or seed banks’ as we now live in a
time of unprecedented mass extinctions of species as a result of: (a) loss of habitat;
(b) pressure from non-native species; (c) over-harvesting; (d) all three.
17.Crop breeders nowadays often turn to the wild relatives of crops for key
characteristics like: (a) disease resistance; (b) colour; (c) number of seeds; (d)
height of plants.
18.Genetic diversity gives species the ability to adapt to: (a) changing environments;
(b) new pests and diseases; (c) new climatic conditions; (d) all three.
[18]
Each of the following questions consists of an item in the first column and two
statements in the second column (numbered 1 and 2). Consider which statement(s)
relate to the item.
A if only statement 1 relates to the item
B if only statement 2 relates to the item
383
C if both statements 1 and 2 relate to the item
D if neither statement 1 or 2 relate to the item
Item Ans Statements
1.Differential reproduction results 1.being able to get less food

from …
2.some individuals being more
protected from predators
2.Natural selection 1.relies on variation in populations
2.proves evolution
3.Artificial selection 1.is a direct analogy to the process of

natural selection
2.uses the variability in the gene pool
4.Transformation of a wild grass 1.has happened in the last few 100

(teosinte) into maize years
2.is because of the narrow diversity of

the teosinte genome
5.Domestication 1.results in the production of modern

food crops and livestock
2.is the feeding and keeping of farm

animals
[5]
3. True and false

incorrect word/term. In the space, write the correct word/term.
Statement T/F Correct term
1.Artificial selection mimics natural 1

selection. ________________________________
2.Populations would increase 2

exponentially if all individuals born ________________________________
reproduced successfully.
3
3.Mutations are the only source of new ________________________________
384
alleles. 4
________________________________
4.Those individuals whose inherited
characteristics best fit them to their 5
environment are likely to leave fewer ________________________________
offspring than those that are less-fit.
6
5.The product of artificial selection is ________________________________
the adaptation of populations of
7
organisms to their environment.
________________________________
6.Natural selection is a random
8
process.
________________________________
7.There is variation in some
9
populations.
________________________________
8.Cultivated plants show higher levels
10
of phenotypic variation than wild plants.
________________________________
9.‘Fitness’ does not mean speed,
beauty, intelligence, etc., it means
ability to survive and reproduce.
10.Germ cell mutations play by far the

most important part in generating
evolutionary change.
[10]
4. Mix and match
Match each description in Column B with one corresponding item in Column A and
write your answer in the space provided.
1.The mating of closely related individuals 1.______ A.natural selection
2.Creates individuals with new combinations of 2.______ B.artificial selection

alleles
3.______ C.sexual
3.The selective breeding of domesticated reproduction and
4.______
plants and animals to encourage the meiosis
occurrence of desirable characteristics 5.______
D.variation in genes
4.Can store more food to produce bigger, 6.______
E.phenotype
healthier seedlings
385
5.Result of competition between organisms for 7.______ F.domesticated
resources plants
8.______
6.The basis for evolution G.larger seeds
9.______
7.The main process by which species adapt to H.inbreeding
10.______
the environment
I.have great genetic
8.Combination of genetic makeup and variability
environmental influences
J.differential
9.Organisms that are genetically distinct from reproduction
their wild ancestors
10.Reason for retaining wild relatives of crop

plants
[10]
5. Terms
Write down the correct term for each of the following statements in the space
provided.
Statement Term
1.Darwin’s mechanism of evolution. 1______________
2.The only source for new alleles. 2______________
3.Controlled breeding by using the idea of selection. 3______________
4.The cultivation of plants or breeding animals by artificial 4______________

selection to make them more useful to humans.
5______________
5.The process of change that enables species to adapt or
new species to develop from pre-existing species over time.
[5]
4.3 Formation of new species
Where do new species come from? That is a key question that the biological
scientists have been asking for more than 200 years.
Together Charles Darwin’s explanation of natural selection, Gregor Mendel’s

experiments with basic genetic inheritance, and some more recent discoveries are
providing answers.
What is a species?
386
A species is a group of organisms that closely resemble each other and are able to
breed among themselves, but not with any other species, and produce viable
offspring.
What is a population?
A population is a group of individuals of the same species occupying a particular

habitat.
Natural selection only operates on variation in inherited characteristics
If all individuals of a population were genetically identical, there would be no natural

selection. There must be some genetic variation within a population, which can
influence the nature of the offspring, so that environmental conditions can select the
best adapted individuals.
Darwin’s greatest difficulty was a lack of understanding inheritance. Gregor Mendel

did publish his ideas in Darwin’s lifetime, but Darwin was unaware of them.
What causes variations in individuals in a species?
There are various factors that contribute to variation amongst individuals of the same
species. The two main ones are sexual reproduction (genetic recombination during
meiosis, chance fertilisation and random mating) and mutations.
A. Sexual reproduction
Meiosis
During meiosis there is a rearrangement or shuffling of the genetic material. This

includes:
–the random arrangement of homologous chromosomes on the equator.
–crossing-over when bivalents form. This will have been explained in the unit on
Meiosis.
This results in the formation of a new combination of alleles.
Chance fertilization
During fertilization the genetic material from the female and male gametes
recombines. There is no choosing of which male gamete will fuse with which female
gamete. As a result a variety of genotypes (genotypic combinations) are formed in
the offspring. The altered genotypes may or may not appear in the phenotype.
Random mating
Random mating means that every female gamete, with her particular genotype, has
an equal chance to be fertilized by every male gamete, with his particular genotype
in the population.
387
B. Mutations
A mutation is any sudden alteration in the genetic makeup (genetic code) of an

organism. They have been explained on page 175.
While mutations can occur in somatic and gametic cells in biological evolution we are
only interested in this section in gametic mutations.
Gametic mutations occur in gametes and can give rise to offspring that carry the
mutation in all of its cells. These mutations, known as germ-line mutations, can be
passed on to the offspring and have a strong influence on evolution.
germ-line = in the eggs or sperm
Changes in base sequences of DNA. This is the main way new alleles are created
and is the main source of genetic variation.
Whole chromosomes may be deleted or duplicated, and even the entire

chromosomal compliment can multiply in a process called polyploidy. Polyploidy is
very important in the evolution of new species of plants. See page 228.
A small percentage of mutations, in the case of evolution beneficial ones, result in a

change in the phenotypes. If the change results in organisms adapting better to new
or unfavourable conditions, they will survive and breed more successfully than the
rest of the population. This is natural selection as nature has selected the better
adapted to survive and breed. In time the whole population will have the new
genotype and a new species will have been formed, i.e. evolution has taken place.
Variation in populations due to mutations
The following examples show variation in populations due to mutations.
The different beak forms of Galapagos finches
These are pointed and blunt. These differences allowed the finch to occupy the new
niches available on the islands and to feed on different types of food. This difference
has a genetic basis as it has been found to be a mild mutation. This variation
allowed, over time, the development of different species of finch.
White lions have a harmless mutation that results in their colour varying from blonde
to near-white. This colouration does not appear to disadvantage their survival; they
have been reintroduced into their natural habitat and have been hunting and
breeding successfully with other lion for a significant amount of time.
Resistance of bacteria to antibiotics
Bacteria breed very rapidly. As a result their populations become enormous. Within
388
these vast numbers the chance of mutations occurring is high. The mutations will
create considerable genetic variation. When exposed to an antibiotic, most bacteria
die, but some variants have a mutation that makes them resistant to the effects of
the antibiotic.
These bacteria will survive and reproduce. As this process continues through several
generations and with repeated exposure to the same antibiotic, a population of
antibiotic-resistant bacteria will evolve.
Learning activity 1
Causes of variation in individuals
Devise a clear, simple learning diagram to show the main causes of variation in
individuals.
What are the effects of inbreeding and outbreeding in a population?
Inbreeding
Inbreeding is mating of genetically closely related individuals.
In nature inbreeding in a population:
leads to a loss of genetic diversity, which in nature will prevent evolution.
results in homozygosity, which can increase the chances of offspring being affected
by recessive or harmful traits thus increasing the chances of genetic disorders. In
nature this can decrease the biological fitness of a population, i.e. reduces its ability
to survive and reproduce. This leads to what is known as inbreeding depression.
When this happens:
–animals have a lower birth weight, do not reproduce so successfully and have less
resistance to disease, predation and environmental stress.
–plants produce less seeds, seed germination is poor and their resistance to stress
is less.
Therefore, inbreeding depression can lead to an increase in extinction rates.

389
Humans use inbreeding to try and establish a new and desirable trait or to continue
particular characteristics in an animal or plant group. However, it often leads to loss
of vigour and poor survival as the offspring can become homozygous for a higher
proportion of undesirable recessive genes. These undesirable traits can, however,
be eliminated through further selective breeding or culling.
Outbreeding
Outbreeding or outcrossing is the production of offspring from the mating or breeding

of genetically unrelated individuals.
In nature outbreeding in a population:
leads to an increase of genetic variation, which increases the chance of evolution.
promotes heterozygosity, which decreases the chances of offspring being affected

by recessive or harmful traits.
is a way by which new desirable traits can be introduced into the population that will
have a positive effect by increasing the vigour, size and fertility of the offspring. In
nature plants that outbreed outperform self-pollinating (inbreeding) individuals.
Humans use outcrossing to add desirable and remove undesirable traits in both
plants and animals. The vast assortment of new varieties of plants is due largely to
outbreeding techniques where new desirable traits are deliberately bred into plants
by crossing.
Learning activity 2
Inbreeding and outbreeding - effects
Devise a clear, simple learning diagram to show the effects of inbreeding and
outbreeding in natural populations.
Inbreeding in humans
Inbreeding in humans is the mating of close relatives such as mother to son,

father to daughter, brother to sister, first cousin to first cousin, and is sometimes
referred to as incest. There are taboos against incest in many societies and in most
countries it is against the law.
390
taboo = a type of behaviour that is forbidden
Why is human inbreeding so frowned on?
Human inbreeding can easily result in the offspring having a recessive genetic
disease, e.g. Tay-Sachs and haemophilia. The following information will explain why.
Close relatives are much more likely to carry the same mutation for a recessive
genetic disease. They would thus be ‘genetic carriers’ of the disease or physical
abnormality.
Thus, if the parents are related it increases the chances of the offspring receiving a
harmful recessive allele from each parent.
If this happened the offspring would be homozygous for the harmful recessive
alleles, which would be expressed in the offspring who would suffer from the genetic
disease.
What are the risks of being homozygous for a genetic abnormality?
The risk of a genetic disease resulting from mating with:
a common ancestor is about 1 in 20
first cousins is about 1 in 11
first degree relatives is 1 in 2
Therefore, it can be seen that the closer the relationship the greater the risk of
harmful recessive alleles being homozygous in the offspring and thus being
expressed.
An example of human inbreeding
Inbreeding was very common among the royal families of Europe, and it is likely to
have been the cause of the widespread number of cases of haemophilia in the royal
families in the 1900s.
The presence of haemophilia in the royalty of Europe started with Queen Victoria of
England. It seems that a haemophiliac gene arose by mutation in one of the gametes
of her parents. Of her nine children one, a son, was a haemophiliac and two
daughters were genetic carriers. The haemophiliac gene is recessive and X-linked.
Being sex-linked means only the sons would suffer from the disease.
Queen Victoria
Inbreeding in the royal family was seen as a major reason for the harmful recessive
allele’s high incidence rate in the British royal house. Haemophilia spread rapidly
391
with over twenty members inheriting the disease in just over 100 years. This
recessive gene has since been lost in this lineage.
haemophilia = the blood clots much more slowly than normal, resulting in extensive
bleeding from even minor injuries
Females are carriers for this rare blood-clotting disease when one of their X
chromosomes contains the harmful recessive allele. Males inherit the disease if their
X chromosome (from their mother) carries the gene for haemophilia.
Blood clots slowly
Another example of a genetic disease being caused by inbreeding is the increased

prevalence of Tay Sachs disease in certain Jewish populations where arranged
marriages are encouraged. It is an inherited metabolic abnormality that is fatal in
early childhood.
An example of outbreeding in plants
A good example of plant outbreeding was the deliberate breeding in the Brassica
family. This resulted in a large number of well-known vegetable varieties - kohlrabi,
kale, broccoli, cauliflower, Brussels sprouts and cabbage. The outbreeding was done
by using traits desirable for enlarging certain parts of the parent plant, e.g. for stem
production (kohlrabi), for large leaves (kale), compacted flower buds (broccoli), etc.
Although they appear diverse, all brassicas arose from the outbreeding of just a few
species of wild Brassicas, i.e. the wild mustard plants.
Diagram to show how outbreeding resulted in very different varieties
Note:
Brassica vegetables are one of the dominant food crops worldwide. They are high in
vitamin C and soluble fibre and contain multiple nutrients and phytochemicals.
Do you eat plenty of them? It would improve your health if you did.
Founder effect
The founder effect refers to the loss of genetic variation when a very small number
of individuals from a larger population establish a new colony. This is usually due to
migration or geographic isolation.
392
Diagram to show how a founder population arises
If the new population has only a few individuals, its gene pool may be quite different
from that of the original population. As a result over time they will establish a new
population. The new population will be different, both genetically and phenotypically
to the parent population. Eventually the founder population can become a new
species, related to the original but unable to interbreed.
This potential for relatively rapid changes in a colony's gene frequency has led most
scientists to consider the founder effect an important driving force in the evolution of
new species.
Founder effect in action
Animal example of founder effect
A common example of the founder effect in South Africa is the cheetah (Acinonyx
venator).
Until recently, it was thought that reason for the decrease in their population was due
to over-hunting and habitat destruction. However, recent genetic analysis, e.g. with
mtDNA, shows that the cheetah population has an extremely low genetic diversity
(90 to 99% less genetic variation than in other out-bred cat species). This results in
poor sperm quality, low fecundity, high cub mortality and sensitivity to disease. All
these factors have made breeding and survivorship difficult for cheetahs – only about
5% of cheetahs survive to adulthood.
fecundity = the ability to produce abundant healthy offspring
It is hypothesised that about 10 000 years ago due to climatic change a major
extinction of large vertebrates occurred. All but a small group (the founder
population) of cheetahs died out forcing close family relatives to mate with each
other, or inbreed. This caused their low genetic diversity, much lower than the
original population. This can make the population very vulnerable to extinction.
Cheetah (Acinonyx venator).
Note:
The low genetic diversity of the cheetah is neither complete nor permanent. A
moderate level of variation has accumulated over time. Captive breeding
management plans are hopefully going to lessen inbreeding effects, e.g. breeding
between subspecies is being encouraged.
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Concepts of convergence and divergence in evolution
Groups of species undergo various kinds of natural selection and, over time, may
engage in several patterns of evolution: convergent evolution, divergent evolution,
parallel evolution and co-evolution.
Convergent evolution
Convergent evolution is the process during which species that are not closely related
to each other independently evolve similar kinds of traits to adapt to similar
environments or ecological niches.
For example:
Bees, hawks, and bats all have wings.

None of these organisms owes its wings to genes inherited from any of the others,
i.e. they were not present in the last common ancestor of each. Each kind of wing
evolved independently, suggesting that the trait of flight is a useful one for the
purpose of survival and reproduction. These independently evolved wings are called
analogous structures. These animals ‘converged’ on this useful trait.
Convergent evolution of flight in insects, bat, bird and pterodactyl (extinct)
Flightlessness has evolved in many different birds independently. For example the
ostrich (South Africa), emu (Australia), cassowary (Australia), rhea (South America)
and kiwi (New Zealand) are all not related.
Convergent evolution of flightlessness in birds
L to R – ostrich, emu, cassowary, rhea and kiwi
Divergent evolution
Divergent evolution is the process in which a trait held by a common ancestor

evolves into different variations over time. A common example of divergent evolution
is the vertebrate limb trait. The human, horse, bat and bird fore-legs and the whale
flipper most likely evolved from the front flippers of an ancient jawless fish. Because
they share a common evolutionary origin, these are examples of homologous
structures.
Various vertebrate fore-limbs

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An important result of divergent evolution is speciation, the divergence of one
species into two or more descendant species.
Learning activity 3
Convergent and divergent evolution
Using no words, design a simple learning diagram to show these two concepts.
How does speciation occur?
What is speciation?
Speciation is the evolutionary formation of new species that are genetically

distinct from the older, parental species.
Speciation is most often due to one species dividing into two or more species, which
is called cladogenesis. The diagram below shows such speciation in fruit flies. The
branching points on this partial Drosophila phylogeny represent speciation events
that happened in the past.
Speciation
What is extinction?
Extinction is the permanent loss of all members of a species.
Well-known examples of extinct species are the dinosaurs, dodo and sabre-toothed
tigers. Most of the extinctions are thought to have resulted from environmental
changes.
After a mass extinction speciation occurs more easily as there is less competition. Of
the estimated four billion species that have evolved since life appeared on earth
extinction has been the fate of the vast majority of them.
The reason why there is still life on earth is that extinctions are, at least on geological
timescales, naturally balanced by the formation of new species: speciation is a
constant driver of biodiversity.
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What causes speciation?
Each population contains genotypic variations. These variations are important as

they increase a species’ chance of adapting and thus surviving under different
conditions. Variation can eventually lead to speciation.
There are two major types of speciation:
geographic (allopatric) speciation, which is due to part of the population becoming

isolated.
sympatric speciation, which occurs in a population that occupy the same

geographical area.
The following diagram shows the two main types of speciation.
Geographic (allopatric) speciation
Geographic speciation occurs when a new species is formed as a result of the whole
or part of a population becoming geographically isolated from the ancestral
species. It is the most common form of speciation in animals, but not in plants.
How do populations become geographically isolated?
In the past, isolation could have been due to geological events such as erosion,
earth quakes, volcanoes and continental drift.
Today, geographic speciation could start when:
–a lake dries, forming two separate smaller bodies of water.
–a few seeds stuck on a bird’s feather fall onto a newly formed island.
–sea currents wash a few lizards or insects onto an island with no such organisms.
How does geographical speciation occur?
The diagrams alongside illustrate geographic speciation.
If a population of a single species:
becomes separated by a geographical barrier (river, sea, mountain, lake) then the
population splits into two populations. See A and B.
There is now no gene flow between the populations. Diagram 2.
Since each population may be exposed to different environmental conditions

(environmental pressures/selective forces) natural selection occurs independently in
each of the two populations.
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Each population adapted to its particular environmental conditions. In this example,
the two areas differed in terms of how dry and hot they were.
The individuals of the two populations become very different from each other
genotypically and phenotypically.
Even if the populations were to mix again they will not be able to reproduce with
each other.
They have thus become different species - speciation occurred.
Diagrams to illustrate geographic speciation
Learning activity 4
Geographic speciation
By studying the preceding text in conjunction with the diagrams alongside, answer
the questions below. Not all the answers will be found in the text and diagrams; you
will need to think back to things you learnt in Grade 10 and 11.
1.Explain why some animals, given the chance, move into new environments. (3)
2.In this example, describe the climate in the region where the species originally
existed. (2)
3.In B, to which environmental pressures did selection promote tolerance? (2)
4.From what you learnt in Grade 10, what environmental event causes sea levels to
drop and rivers to dry up? (1)
5.What other physical barriers could isolate different parts of a population? (3)
6.Apart from what you mentioned in Question 3 list four other types of selective
forces that could have had an effect on a gene pool? (4)
7.1In which area did selection promote tolerance to hotter and drier conditions? (1)
7.2In this area tortoises were paler, taller (more humped) and larger than in the
cooler, wetter area. What were the advantages to the tortoise of having these
features in this environment? (4)
Total [20]
Sympatric speciation
Sympatric speciation is when a new species arises in the same area as the
ancestral species without any geographic isolation.
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Plants frequently develop new species by a combination of polyploidy and
hybridisation, creating an individual that is instantly different and cannot interbreed
with the parental species even though they are living in the same area, i.e. they are
sympatric. Sympatric speciation is very important in plant speciation.
Examples of geographic speciation
The syllabus requires that learners study one example of geographic speciation,
either Darwin’s Galapagos finches or cichlid fish in Lake Malawi.
Galapagos finches
Being volcanic the Galapagos Islands emerged from the sea relatively recently.
Initially they obviously had no land organisms. Therefore all evolution of the islands'
unique animals and plants has occurred within the past 3 to 4 million years, a short
period in geological terms.
Galapagos Islands
How did the ancestral finch group find their way to the islands?
A recent suggestion is that an ancestral group, driven by strong winds, from the
nearest mainland about 1 000 kilometres away landed on one of the islands. This
group would give rise to all 14 Galapagos finch species found on the islands.
All these finch species are sparrow-sized and similar in appearance but they differ in
beak structure and feeding habits.
How did the different species arise?
After arrival on an island the finches remained permanently isolated from their point
of origin, the South American mainland and were free to evolve because there was:
an absence of pre-existing predators.
no competition from other land birds as there were none there.
a variety of empty ecological niches, each with its own type of food.
What are the stages in the speciation process?
It seems that finch speciation occurred firstly as a result of division of habitat and
then by division of food resources.
1.Division of habitat
A single finch ancestral species divided into two lineages each occupying different
habitats – the ground and tree finches.
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2.Division of food resources by trophic (feeding) specialisation
As the finch population grew and there were periods of food scarcity competition for
food resources increased.
With the large variety of feeding niches open, the early finch species developed
feeding specialisations to get food from different sources. This resulted in them
evolving into the variety of finch species we know today.
The size and shape of the beaks clearly reflect their specialisations, for example:
–grasping beaks, e.g. the tree finch, which eats buds, fruit and insects.
–crushing beaks, e.g. the vegetarian finch, which eats seeds, and the ground finch,
which eats ticks and blood of sea birds.
–probing beaks, e.g. the cactus finch, which probes cactus fruit for seeds, and the
woodpecker finch, which uses small twigs and cactus spines to poke into crevices in
dead branches for insect larvae.
It seems likely that trophic specialisation was at the centre of finch speciation.
Galapagos finch evolution (showing number of species of each type)
A reminder: the central feature of Darwin’s theory is that species change if there are
environmental changes. Here the ‘changes in environment’ were:
the variety of empty ecological niches each with its own type of food provided
opportunities for change (adaptation).
competition in times of food shortage that provided the selective pressure or need for
change.
Note:
1.It is known that finch speciation occurred during turbulent geologic and climatic
times. The finches' ancestor probably arrived on a lush, tropical paradise, which
became much cooler and dryer over the subsequent millennia. The changing
ecology, geology and geography provided many opportunities for isolation and
specialisation of the finch populations.
2.Of the 29 resident Galapagos land birds, 22 are endemic (unique to the area) and
all of them are thought to have colonised the islands from the South American
mainland.
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Do you feel you know something more about Darwin’s finches and why they are
so important from an evolutionary point of view? Maybe one day you’ll manage to
take a trip to the Galapagos Islands.
Cichlid fish in Lake Malawi
Lake Malawi is a long narrow lake formed by the East African Rift where the African
tectonic plate is splitting in two. This makes the lake relatively young in geological
terms, about one million years old. Initially it was a swampy area and not suitable for
supporting fish life but later developed into a lake.
Map to show position of Lake Malawi
Lake Malawi is one of the Great Lakes of Africa, the others being Lakes Victoria and
Tanganyika.
As they are isolated from each other and the rest of the world, they are ideal places
to study speciation as geographical separation (isolation) is considered to promote
speciation. The enormous diversity of cichlids in these lakes (about 1 300
scientifically described species) has become important in the study of speciation
during evolution.
If only fourteen Galapagos finch species inspired Darwin and resulted in his
theory of natural selection, maybe the thousand plus cichlid fish species will have a
great deal more to reveal about the processes of speciation.
In Lake Malawi, sometime between 570 000 ya and 1 mya a single ancestral group
arrived and diversified extremely quickly, eventually giving rise to as many as 600
cichlid fish species. They have a wide diversity of body shapes, ranging from
strongly laterally compressed species through to species that are cylindrical and
highly elongated. They range in length from about 2.5 centimetres to 1 metre.
Some examples of cichlid fish
How did the different species arise?
The evolution of the different cichlids is a good example of sympatric

speciation. One possible reason for this extraordinary diversification is that the
ancestral group remained permanently isolated and was free to evolve easily
because:
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the lakes provided a variety of empty ecological niches, each with its own type of
food.
with no other fish there was no competition.
there was an absence of pre-existing predators.
The cichlid fishes of Lake Malawi and the other lakes have undergone one of the
most rapid adaptive radiations or cladogenesis of any known vertebrate group.
Because diversification has been so recent, and rapid, scientists are able to study:
very early stages of diversification
the process of speciation
patterns in the speciation processes. Such studies have suggested a three-stage

pattern, each with its own selective forces. These patterns may apply generally to
the evolutionary origins of many other vertebrate species.
Modern genetic techniques are uncovering a great deal more than was previously
understood about the cichlid speciation processes.
What are the stages in the speciation process?
1.Division of habitat
A single cichlid ancestral species diverged into two major lineages each occupying
different habitats, the sandy bottoms and patches of rocky outcrops –
the sand and rock-dwellers. As there was enough food for the early cichlids there
was little interspecific competition.
2.Division of food resources
The ancestral cichlid species probably had a varied diet, eating whatever was
available.
As the cichlid populations grew, competition for the food resources increased.
In the newly formed lake there was, however, a large variety of unoccupied feeding
niches.
Therefore fish with adaptations for getting food from different resources, e.g.
algae, plankton, insects, other fish and snails became the next basis of selection.
Feeding adaptations of some cichlids
It is generally considered that trophic (feeding) specialisation is at the heart of

the enormous cichlid diversification, with each species showing great
specialisation for a distinct, fairly narrow food niche.
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What enabled the cichlid fish to adapt to such narrow food niches?
The cichlids have a unique and strange characteristic; they have two pairs of
jaws – the usual outer jaws as well as a second pair (pharyngeal jaws) that are
invisible and lie within the throat area. The outer, highly specialised jaw collects the
food while the inner jaw chews it.
It has been proposed that the jaw adaptations were the ‘key-innovation’ that set off
their explosive radiations. The jaw adaptations allowed cichlids to take advantage of
every possible food resource and evolve into a great variety of feeding
specialists. ‘Key innovations’ are often linked to a remarkable diversification of
species, e.g. flight in birds and insect pollination in angiosperms.
3.Division by sexual selection
The radiation of cichlid into diverse species was initially due to adaptation to habitat
and then adaptation to different food resources. Subsequent diversification was due
to sexual selection.
This last stage includes numerous reproductive strategies (methods), all based on
behaviours and colours that communicate reproductively important information.
These have significantly contributed to the extraordinary variety of cichlid species.
Sexual selection leads to the evolution of male traits for the attraction of females and
of female preferences for these traits. These strategies include:
–complex mating behaviours, for example:
➢elaborate male courtship displays, whereby male cichlid build intricate nests,
known as bowers, which females inspect in order to decide which males they should
best mate.
➢females being polyandrous, i.e. having multiple male partners.
–differentiation of male breeding colouration. In this way, the females select not only
the best male, but also a male of her same species. Many closely related species
differ mainly in male colour pattern.
Learning activity 5
Speciation
Question 1
1.Why is it important that populations have genetic diversity for speciation to occur?
(1)
2.Is the most common form of animal speciation geographic or sympatric? (1)
3.What does the term ‘viable’ mean? (1)
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[3]
Question 2
Places where geographic speciation can be studied easily.
Answer either the question on the Galapagos Islands or Lake Malawi
Galapagos Islands
1.Why were the finches isolated from their ancestral species? (2)
2.Why could the finch speciate so rapidly on the islands? (2)
3.How did the finch species first diverge? (1)
4.How many finch species are there on the islands? (1)
5.After the initial divergence, what probably acted as a stimulus for further
speciation? (1)
6.How did the finches adapt to this? (2)
7.Why can the 14 Galapagos finch species not interbreed? (1)
8.Why is this type of speciation called adaptive radiation? (2)
[12]
Lake Malawi
1.Why did speciation take place so recently, geologically speaking, in Lake Malawi?
(2)
2.Why was the ancestral group isolated? (1)
3.Approximately how many cichlid fish species are there in Lake Malawi? (1)
4.What was probably the first stage of speciation? (1)
5.Why would there initially have been plenty of food for the fish? (1)
6.As food resources became more limited, the fish needed to adapt if they were to
survive. What unique characteristic allowed this? (1)
7.Why did this allow the fish to diversify? (2)
8.Why is this type of speciation called adaptive radiation? (3)
[12]
Total [15]
Reproductive isolation
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Reproductive isolation is a mechanism that prevents two or more species from
exchanging genes (interbreeding) and producing viable, fertile hybrids even though
they are not geographically separated. Such species that live together are called
sympatric species.
As has been explained, geographic barriers often start the development of new
species, especially in the case of animals. If the isolated groups never come into
contact again, they will almost certainly accumulate enough genetic differences over
time to become separate species. This can take 3 000 to 250 000 years for complete
reproductive isolation.
Once these separate species come into contact again most will not interbreed. This
is probably because some of the differences accumulated during speciation will
prevent breeding it.
These differences were probably incidental adaptations to local conditions during

geographic isolation (allopatry). They did not arise for the purpose of preventing
breeding between different species.
These ‘by-products’ of allopatric speciation, which cause reproductive isolation

and are probably the final stage of speciation.
Mechanisms of reproductive isolation
There are several mechanisms (methods) of reproductive isolation, which can

operate either pre-zygotically (pre-mating) or post-zygotically (post-mating). Most
prevent mating or fertilisation from taking place.
1.Breeding at different times of the year
2.Species-specific courtship behaviour
3.Adaptation of plants to different pollinators
4.Infertile offspring
1. Breeding at different times of the year
Different animal species often have different mating seasons and plants flower at
different times of the year, which prevents mating opportunities.
What are some examples of this?
Two parrot species, the critically endangered Cape Parrot and the Grey-headed
Parrot occur in areas quite close to each other. Both species share similar breeding
habitats but there has been no record of hybridisation as they breed in different
seasons – the Cape Parrot breeding from August to February and Grey-headed from
April to August.
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Grey-headed parrot
Cape parrot
Two species of eagle that live in the same territory, the Tawny Eagle and the
Bateleur, breed in different seasons: the former in winter, the latter in summer.
Tawny eagle
Bateleur
Two fish species of the kob family both spawn in the water off the Kwa-Zulu Natal
coast; silver kob spawns between August and December and the squaretail kob
between June and September.
2. Species-specific courtship behaviour
Courtship behaviour is an animal activity to signal sexual readiness for pair

formation, mating and reproduction. It is important as an isolating mechanism as it
prevents different species from interbreeding even though their territories overlap.
Specific courtship behaviour
Examples of this courtship behaviour include:
breeding display, e.g. soaring and calling with occasional claw grappling of the
well-known African fish eagle.
stridulating songs by male cicadas (Christmas beetles), during pair formation and
courtship.
stridulating = to make a chirping or grating sound by rubbing certain parts of the body
together
secretion of pheromones(chemical compounds that bring creatures together to

mate), which may be secreted by special glands or incorporated into other
405
substances, e.g. urine. Pheromones are widespread among insects and vertebrates
but not birds.
breeding plumage, metallic green of the male malachite sunbird.
3. Adaptation by plants to different pollinators
Plants and their flowers have groups of traits (pollination syndromes) that are an
adaptation for particular pollinators.
These traits are floral features that attract particular animals to visit the flowers to
receive and deposit pollen. The features include flower shape, size, colour, scent,
reward type (nectar and/or pollen), timing of flowering, etc.
The flower is designed so that only one specific pollinator can get to the pollen.
For example, some orchids attract their pollinators by sexual deception and mimicry,
e.g. oils that mimic sexual pheromones and flower shapes that imitate the female of
an insect species so that they may attract the males, which, in the process, pick up
and deposit pollen.
Sole pollinator of Disa uniflora - the Mountain Pride butterfly
Flowers that are visited by flies can be:
–foul smelling, e.g. Stapelia gariepensis, a carrion flower that attract flies by
mimicking smell of rotten meat.
–tubular flowers with the narrow opening just wide and long enough for a pollinator’s
tongue to reach the nectar, e.g. Erica irbyana. Horse flies and bee flies with a long
proboscis are examples of such pollinators.
406
Dull-coloured flowers with strong, fruity or musty scents open at night e.g.
baobabs, bananas or mangoes attract pollinators such as bats or mice.
Baobab and bat
The African Lily (Massonia depressa) of the Succulent Karoo region is pollinated by
nocturnal rodent species. Its ground level flowers are adapted to support non-flying
mammal pollinators by being very sturdy. They also have a strong yeasty odour and
vast quantities of sucrose-rich nectar that is very viscous (jelly-like), which the
rodents lap up easily but insects cannot. It is thought that M. depressa co-evolved
with its pollinators.
Rodent on an African Lily
Birds such as sunbirds with long beaks are attracted to unscented flowers that are
large, red, often tubular, have copious nectar and stigmas and stamens that project
to touch bird’s head or beak, e.g. many ericas and aloes. Some strongly curved
tubular corollas, e.g. many ericas, match the bill shape of their chief pollinator, the
orange-breasted sunbird. This ensures that the bird will have less competition for
that flower. The flower is thus assured that the specific pollinator will carry the pollen
to flowers of the same species, increasing the likelihood of fertilisation. This
efficiency prevents wasted pollen and effort as well as interspecific reproduction,
further isolating the plant species.
4. Infertile offspring
Even if two different species mate and produce hybrid offspring that are vigorous, the
species are still reproductively isolated if the hybrid offspring are sterile, i.e. they
cannot produce offspring. This is an example of post-zygotic reproductive isolation
as it occurs after fertilisation.
What is an example of this?
The classic example is the mule, which is the result of a cross between a donkey
stallion and a horse mare. Mules are vigorous, healthy animals, but they are sterile,
i.e. they are unable to reproduce successfully because they are unable to produce
normal gametes as the chromosomes do not pair and cross over correctly during
meiosis. Female mules sometimes produce viable eggs but males are infertile.
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Learning activity 6
Short questions
1. Multiple choice
answer below.
1 2 3 4 5 6 7 8 9 10
1.Cladogenesis is: (a) the evolution of a new species from an ancestral species. (b)
the diversification of a species into two or more species as groups adapt to different
environments. (c) the process by which ultraviolet radiation causes mutations that in
turn result in evolution. (d) non-random natural selection within populations and
species.
2.The evolution of one species into two or more species as a result of different
populations becoming reproductively isolated from each other is: (a) geographic
speciation; (b) creationism; (c) photosynthesis; (d) cloning.
3.The process by which a population becomes better suited to its environment is

known as: (a) accommodation; (b) adaptation; (c) variation; (d) acclimation.
4.Populations of the same species living in different places: (a) do not vary; (b)
become increasingly different as each population becomes adapted to its own
environment; (c) are genetically identical to each other; (d) all three.
5.Bird populations that do not interbreed because they cannot recognise each
other’s mating calls are examples of: (a) ecological isolation; (b) geographic
isolation; (c) isolation by species-specific courtship behaviour; (d) post-zygotic
isolation.
6.A change in the genetic composition of a population over successive generations

is called: (a) emigration; (b) mutation; (c) natural selection; (d) evolution.
7.A hummingbird would be considered a specialist species because: (a) it can only
eat one certain type of food; (b) it can live in a variety of habitats; (c) it can tolerate a
wide range of temperatures; (d) only a and c are true.
8.Which of the following statements is false? (a) Genetic diversity helps prevent a
species from becoming extinct. (b) The phenomenon in which animals with
favourable adaptations reproduce more rapidly is called differential reproduction.
(c) Geographic isolation is a common mechanism contributing to speciation. (d) By
definition, the fittest animals are the largest and strongest animals.
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9.Geographic isolation may result from: (a) a volcanic eruption; (b) a river; (c) a
mountain range; (d) all of these answers.
10.Which selection is correct? Mechanisms of reproductive isolation that may

contribute to speciation include:
1Species-specific courtship behaviour
2Breeding at similar times of the year
3Adaptation to different pollinators (plants)
4Fertile offspring
(a) 1 and 2; (b) 1 and 4; (c) 3 and 4; (d) 1 and 3
[10]
2. Terms
Give the correct term/word for the following descriptions.
Description Term
1.The type of evolution when one species gives 1_________________________

rise to a large variety of new species,
2_________________________
particularly when there are many vacant
ecological niches. 3_________________________
2.A group of organisms able to breed among 4_________________________

themselves and produce viable offspring. 5_________________________
3.Type of evolution by which unrelated or
distantly related organisms evolve similar body
forms, coloration, organs and adaptations.
4.A behaviour in animals that signals sexual

readiness.
5.The most common type of speciation.
[5]
3. True and false

incorrect term. In the space, write the correct term.
Statements T/F Correct term
409
1.Populations that become isolated by means of 1_________________________
a geographic barrier will differ from their
2_________________________
ancestral species.
3_________________________
2.Somatic mutations have a strong influence on
evolution. 4_________________________
3.Genetic barriers, e.g. seaways, mountains, 5_________________________

divide populations causing them to diverge.
4.Beak-size variation in Darwin’s finches is a

classic example of speciation in action.
5.Reproductive isolation prevents two or more

populations from exchanging genes.
[5]
4. Mix and match
Match each description in column A with one in column B and write the correct letter
in the space provided.
Column A Answer Column B
1.Individuals that can 1._________________________ A.evolution

interbreed
2._________________________ B.adaptation
2.Competition, predation,
3._________________________ C.division of
climatic factors and
habitat
disease and parasitism 4._________________________
D.selective forces/
3.Formation of numerous 5._________________________
environmental
species from a single
6._________________________ pressures
ancestor
7._________________________ E.adaptation to
4.Adjustment of a living
various pollinators
organism to its 8._________________________
environment 9._________________________ F.geographic
(river, mountain,
5.The process by which 10.________________________
desert)
new organisms develop as _
a result of changes in G.anagenesis
genetic material H.adaptive
6.Place from which radiation
members of an ancestral I.species
species disperse to form a
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new species J.point of origin
7.Possibly the cause of the

first stage of speciation
8.Mechanism of
reproductive isolation
which may contribute to
speciation in plants
9.Change within a single

evolutionary line (lineage)
with no branching
10.Primary isolating
mechanism for speciation
[10]
Total [30]
Hominid Studies
There are two important questions that many of us humans have always pondered
on.
where do we come from?
what is our relationship to all organisms that live, and have lived?
411
Characteristics that humans share with African apes
To trace the evolutionary development of modern humans from an ancestor shared

by all hominids, it is helpful to consider their anatomical similarities, and of course,
their differences. The differences point to the existence of different species, while the
similarities point to a possible common ancestor.
Key terminology
arboreal living primarily in trees
opposable thumb a thumb that can be placed opposite the fingers of the same
hand
sexual distinct differences in size or appearance between the sexes of
dimorphism an animal in addition to the sexual organs themselves
412
bipedalism ability to walk on two legs
quadrupedalism use of four limbs for locomotion (quadrupeds)
diurnal active during the day rather than at night.
foramen magnum hole in the base of skull through which the spinal cord passes
ridge running across the top of the skull that served to attach
cranial ridge
large jaw muscles to the head
prognathous protruding (projecting forward) upper / lower jaw
Similarities that humans share with African Apes
Hominids (members of the Family Hominidae, including humans) share a number of

characteristics. Scientists argue that these arose from their adaptation to arboreal
living (life spent mostly in trees). The main similarities are given in Figure 3 below.
large brain
eyes in front
freely rotating arms
long upper arms
rotation around
elbow joints
opposable
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Large brains: relative to their body size, hominids have larger brains than
other species in the Animal Kingdom. This allows them to process and store
information.
Two eyes in the front of the head (Figure 4): this provides good binocular
vision as both eyes work together. The eyes have cones for colour vision that
gives greater clarity.
Figure 4: the eyes of a chimpanzee in the front of the head.
Freely rotating arms: arms can be lifted above the head to swing from
branch to branch, or to pick fruit hanging relatively high above the
ground.
Long upper arms / front limbs: apes are normally quadrupeds, and this
requires longer front limbs. Longer front limbs also make it easier to grasp and
swing from branches.
Rotation around elbow joints: this allows the limb to extend or flex to grasp
and reach for objects. It also enables the flexing and rotation of the wrists.
Bare fingertips or nails instead of claws: Digits (finger and toes) have soft,
broad and very sensitive pads. The flat finger nails or toe nails protect these
pads.
Opposable thumb: the thumbs of hominids are positioned so that it can

oppose other digits, enabling the hand to grip an object. See Figure 5 below.
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Upright posture: the back limbs of hominids are generally stronger than their
front limbs, enabling them to stand erect (upright) and use their hands for
grasping; standing erect also gives a better view of surroundings and
exposure of genitals to attract the opposite sex (Figure 6).
Sexual dimorphism (Figure 7) – this refers to differences between males and

females of the same species. Humans and apes are sexually dimorphic. This
is linked to competition.
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Figure 5: Figure 6: Figure 7:
opposable thumb upright posture sexual dimorphism
Hominids share some other characteristics as well. They …
lack a tail (that other primates – baboons, monkeys, etc. use for balancing or
sometimes as an extra limb), and
are diurnal – active during the day rather than at night
Note: Scientists hypothesise that humans and modern apes share a common
ancestor. They do NOT believe that a chimpanzee is our direct ancestor.
Anatomical differences between African apes and humans
Many of the anatomical differences between modern humans and other apes are
related to habitual bipedalism. All apes are capable of upright posture and at times
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walking on two feet (gibbon in Figure 8 below). Usually however, the other apes are
knuckle-walkers, moving or scampering (run with quick light steps) on all four limbs.
A B C
Figure 8: Modes of walking: A – a chimpanzee walking on all four

legs, B - a man walking upright on two legs and C - a gibbon
scampering on two legs
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Advantages of bipedalism
Humans can also crawl on all fours but tend to stand erect and walk on two legs in
an upright position. This is known as bipedalism. The trend in human evolution has
been towards bipedalism.
Bipedalism brings with it a number of significant advantages.
Hands are free to pick or carry food, to use tools and handle weapons
Standing upright, with eyes higher off the ground, gives a better, wider view of
surroundings, a timelier warning of approaching predators or of potential prey.
Movement becomes easier and more energy-efficient.
A more vertical posture reduces the body’s exposure to sunlight when in an open
area (60% less than for quadrupeds). It also raises a large percentage of the
body away from the hot ground, where it is exposed to cooling breezes.
In courtship behaviour, the male sex organ is readily displayed.
Anatomical differences as a result of bipedalism
The position of the foramen magnum – the hole in the base of the skull where
the spinal cord leaves / enters the skull – has changed position. As human
evolution has progressed, Quadrupeds have the foramen magnum is in a
backward position. Humans, walking upright have it in a forward position
(Figure 9 below). As a result, humans have their skull balanced on top of the
spinal column, hence allowing bipedalism.
foramen magnum
Chimpanzee skull Human skull
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Figure 9: Position of the foramen magnum in chimpanzee and human skull
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The curvature (shape) of the spine – as shown in the Figures 10A and B:
Figure 10A: the human spine is Figure 10B: The chimpanzee’s spine is
curved so the upper body (and much less curved. As a result, when
the centre of gravity – the red standing erect, the ape’s weight pulls it
line) is directly above the pelvis forward, making an upright stance
when standing erect – a more unsteady – a less curved spine (C-
curved spine (S-shaped spine) shaped spine)
The shape of the pelvic girdle (see Figures 11 and 12 below):
Figure 11A: a chimpanzee pelvis, long

and narrow, is adapted to quadrupedal
knuckle walkin
Figure 11B: The human pelvis

(short and wide) is better able
to support the vertically stacked
human organs.
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Other anatomical differences include: the brain, brow ridges, jaws, teeth,
palate shape and cranial ridge.
Cranial
ridge
Figure 13: Anatomical differences between the skull of a chimpanzee and human
Brain / cranium size (see Figure 13) – as early humans evolved, the brain
grew in size and complexity. Over the course of human evolution, brain size
tripled. Humans have a larger brain (cranium size) than chimpanzees
(apes)
Brow ridges: (as illustrated in Figure 13):
chimpanzees have a well-developed brow ridge above the eye socket.
In humans, the brow ridges are very small or non-existent. As the

human cranium increased in size, the forehead flattened and became
more vertical. As a result, the human brow ridge slowly became
smaller and smaller.
Jaws, teeth and palate shape
As human beings evolved, their diet changed too. The mainly vegetarian diet
gave way to a more varied one, including the meat of animals they caught.
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Once they learnt to control fire and cook their food (making it softer and
easier to chew), the jaws, teeth and palate shape changed, as shown in
Figure 14.
Figure 14: the palate shape and size of canines for chimpanzees and humans
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Palate shape:
a chimpanzee / ape palate is long, and rectangular
the human palate is smaller, almost semi-circular
Canines (sometimes called ‘pointed tooth’, or eye tooth) as illustrated:
The canines for chimpanzees are quite large and pointed.
Human canines are small. Eating softer, cooked foods, the need
for large canines and strong jaws to tear and chew food slowly
disappeared, leading to the reduction in size we see today.
Jaws: as is clear from Figure 14 above
the jaws of chimpanzees and apes protrude forward beyond a

vertical line through the eye. We use the term prognathous to
describe this. Thus, chimpanzees have more protruding jaws,
they have prognathous jaws.
By comparison, humans have relatively small jaws that are

less protruding, less prognathous.
Cranial ridge – a ridge running across the top of the cranium as shown in
Figure 15 below.
A cranial ridge serves as attachment for the muscles involved with chewing.
Adult animals who rely on powerful biting and the clenching of their teeth
have a very large cranial ridge.
In the evolutionary development of modern humans, with a change in diet to

cooked foods that were easier to chew, their jaws became much smaller
and they no longer needed large jaw muscles. And so, the cranial ridge
became redundant and disappeared.
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Figure 15: Cranial ridge on a Paranthropus skull and on a gorilla skull
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Table 1: Summary of differences between modern humans and African apes.
Feature Humans (Homo sapiens) African apes
cranium large cranium / brain small cranium / brain
brow ridges not well developed well developed, prominent
spine more curved (S-shaped) less curved (C-shaped)
pelvic girdle short and wide long and narrow
canines small large
arrangement of
small gaps between teeth big gaps between teeth
teeth
palate shape small, semi-circular long, rectangular
jaws small, less prognathous large, more prognathous
cranial ridges none across top of cranium
foramen magnum in a forward position in a backward position
Activity 2: Anatomical differences and similarities between African apes and

modern humans
Name five characteristics that all hominids share, and name three differences
between humans and chimpanzees. (8)
2. Explain the meaning of the term ‘opposable thumb’ in your own words. (2)
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Explain bipedalism in your own words. Is bipedalism simply the ability to
stand on two feet? (3)

4. Name four advantages of bipedalism. (4)
5. Explain the meaning of binocular vision and depth perception. (4)
6. Use a sketch to illustrate the meaning of the term ‘prognathous’. (3)
Draw a labelled diagram to illustrate the evolution of the palate shape and
teeth from chimpanzee to modern human. The diagram should include at
least three visible differences. (6)
The diagram shows the skulls of two different primate species.
The arrows point

to the position of a
crucial part of the
skull. Answer the
questions below.
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a) What part of the skull are the arrows pointing to in both cases? (1)
Which species, A or B, is more likely to be a quadruped? Explain. (3)
Tabulate 4 directly observable differences between the two skulls. (5)
Explain how the change in the skulls pictured above might indicate a
change in intelligence. (3)
The diagram below gives parts of the skeletons of a human and an ape.
a) Which letter, A or B, best represents a bipedal organism? (1)

b) Explain how the shape of the pelvis contributes to bipedalism. (2)
Which other characteristic shown in the diagram below contributes to
bipedalism? (2)
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(47)
Lines of evidence that support the idea of common ancestors for living
hominids including humans
Here we focus on the progressive evolution of the above characteristics from the
ape-like beings to the humans, using fossil, genetic and cultural evidence to support
the idea of common ancestors for living hominids including humans. Before studying
the major phases of human (hominin) evolution, some terminology, associated with
human evolution must be explained first.
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Fossil evidence
Key terminology
hominin The group consisting of modern and early humans
pithecus Greek word of ‘ape’
Biological classification ranking between family and

genus species, consisting of structurally or phylogenetically
related species
A group of organisms that are genetically similar, can

species
interbreed and produce fertile offspring
For all entries below, the first name: Ardipithecus, Australopithecus and
Homo refers to the genus, the second name, e.g. ramidus, refers to the
species.
Ardipithecus – ardi means ‘ground’, or ‘floor’, and

Ardipithecus ramidus ramidus means ‘root’: the name refers to the closeness
of this species to the roots / origins of humanity
Australophitecus Australis is the Latin for ‘southern’, thus southern ape.
A. afarensis afarensis – from Afar, a location in Ethiopia
A. africanus africanus – from Africa (thus southern ape of Africa)
A. sediba Sediba – Sotho word, meaning ‘natural spring’ or ‘well’
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A. robustus robustus – meaning robust, strong, sturdy, heavy set.
Homo Latin word for human
H. habilis habilis – meaning skilful, or handy
H. erectus erectus – meaning erect, walking upright
Sapiens – wise, thus H. sapiens the wise human (a

H. sapiens
reference to the large brain)
H. ergaster* ergaster – the Greek word for ‘work’, thus working man
H. heidelbergensis* The names of these species are derived from two towns
H. neanderthalensis* in Europe where these species were first discovered
H. naledi* naledi – meaning star.
The major phases of hominin evolution
Human evolution was driven in part by climate change. Climate has always been
variable and organisms could adapt to slow changes. More rapid changes however,
with a scarcity of resources, placed enormous pressure on all organisms to adapt.
Hominins (humans) survived, and flourished, because of their ability to walk

upright, their larger brain’s ability to communicate, to problem-solve, and to make
tools.
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Here we trace the development of hominins from the genus Ardipithecus that
lived about 5 million years ago, to Homo sapiens, the only hominin species
currently living. This development is traced in Figure 16 below.
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Figure 16: The evolution of modern humans – timeframes for the
existence of various hominin species and genera
Understanding human evolution is complex – there is no straight and continuous

line from one species to the next. We only look at a few fossil ‘snapshots’ that
suggest the evolutionary foundations of modern humans.
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Genus: Ardipithecus (Table 2 and 3) – the earliest hominin species (Figure 17)
A small hominin, weighing about 50 kg; 17

fossils found; an intermediate between
apes and humans
Figure 17: Ardipithecus
ramidus
Table 2: Ardipithecus - stats
Species When existed Fossil site (year) Discovered by
A. ramidus 5 – 4 mya Ethiopia (1993) Tim White
Table 3: Ardipithecus ramidus characteristics
Height 1,2 m tall, with a weight of about 50 kg
Brain size 300 – 350 mL, the same size as adult chimpanzee
Foramen magnum a forward position
Brow ridges large / heavy, as in Figure 17 above
Jaws very protruding, prognathous
Canines smaller than for chimpanzee
Pelvis Adapted for bipedal walking and for climbing trees
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Genus: Australopithecus (Figure 18, Table 4
and 5)
Figure 18: The Rift Valley in East Africa.
Fossils for this genus have been discovered only

in Africa, specifically along the Rift Valley and in
South Africa.
Australopithecines lived approximately 4 to

1,6 million years ago.
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Table 4: Australopithecus - statistics
Ethiopia (1974)
A. afarensis 3,9 – 2,8 mya Donald Johansen
Kenya and Tanzania
A. africanus 3,2 – 2 mya Taung (1924); Sterkfontein Raymond Dart
A. sediba 2,0 – 1,6 mya Malapa Cave (2009) Lee Berger
Famous specimen
A. afarensis:
Lucy, discovered 1974, lived 3,2 mya – well adapted for arboreal living, but
had ability to walk upright with proper bipedalism
Laetoli footprints, discovered in 1976 by Mary Leakey – clear evidence for

bipedalism (Figure 19)
Figure 19:
Laetoli
footprint
s
A. africanus: (Figure 20)
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Taung child, discovered 1924 by R. Dart – not initially accepted as
hominin Mrs Ples, lived 2 mya – discovered by Robert Broom at
Sterkfontein caves
Little Foot, lived 3,9 – 4,2 mya – a complete skeleton, found in 1997 by
Ron Clarke
A. sediba: (Figure 20)
Karabo, discovered by Lee Berger – a possible ancestor to the genus Homo
Figure 20: Fossils of (from left to right): Taung child, Mrs Ples and Karabo
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Table 5: Australopithecus – characteristics
A. afarensis A. africanus A. sediba
Height 110 – 150 cm 110 – 135 cm 120 – 130 cm
Brain size 375 – 550 mL 420 – 620 mL 420 mL
Foramen magnum forward position forward position forward position
present, smaller present, smaller

Brow ridges large / heavy
than A. afarensis than A. africanus
Cranial ridge none none none
Jaws very prognathous prognathous less prognathous
Canines large, pointed not very long not very long
intermediate –
fully adapted for fully adapted for
Pelvis bidpedal & tree
bipedal walking bipedal walking
climbing
Australopithecus robustus (dated 2,0 – 1,2 mya)
Fossils from this particular species have been found only in South Africa. The
classification as Australopithecus is uncertain, and the species, together with
another similar species (A. boisei) from Tanzania, are now identify as of the
genus Paranthropus.
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Genus: Homo (2,2 mya to present) (Figure 21 and Tables 6 and 7)
The genus Homo consists of the one still-living species, Homo sapiens – that all
modern humans belong to, and between 15 – 20 extinct species, including
Homo habilis, Homo erectus and Homo naledi.
The most significant difference between this genus and Australopithecus – a

much larger brain (about 30% larger)(see Figure 22 below)
Table 6: Homo stats (Figure 21)
Louis & Mary

Homo habilis 2,2 – 1,6 mya Olduvai, Tanzania (1960)
Leakey
Java, Indonesia (1891)

Homo erectus 2 – 0,4 mya Eugene Dubois
also in SA and Kenya
0,2 mya to
Homo sapiens Omo, Ethiopia (2005) Richard Leakey
present
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Figure 21: Fossil of (from left to right): Homo habilis, Homo
erectus, and Homo sapiens.
Table 7: Characteristics of the three Homo species
Homo habilis Homo erectus Homo sapiens
Height 110 – 130 cm 160 – 180 cm 160 – 180 cm
Brain size 650 mL 900 – 1000 mL 1200 – 1800 mL
Foramen magnum forward position forward position forward position
present, but not none (see Figure

Brow ridges distinct, but small
pronounced 21 above)
Cranial ridge none small none
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Jaws less prognathous less prognathous not prognathous
Canines small small, short small teeth
fully adapted for fully adapted for fully adapted for

Pelvis
bipedal walking bipedal walking bipedal walking
Phylogenetic trees of hominin evolution
We conclude this section by a short review of another example of a phylogenetic tree
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Figure 22:
Phylogenetic
tree of
human
evolution
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4,5
This phylogenetic tree shows aspects of the evolution of Homo sapiens. It shows
very clearly that a number of evolutionary branches, e.g. H. rudolfensis, P.
robustus, etc., became extinct, and more or less when this extinction happened.
The diagram might suggest that there is a single evolutionary line of development
from Ardipithecus ramidus, through A. afarensis, A. africanus, H. Habilis, H. ergaster,
and H heidelbergensis to H. sapiens. However, the process of evolution leads to a
branching pattern of relationships among organisms, not a linear progression.
As the late evolutionary biologist Stephen J. Gould put it, “evolution is a bush, not a
ladder.”
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Genetic evidence to support common ancestry for living hominids,
including humans
Studies comparing the nuclear DNA shared by humans and apes reveal that:
The genetic difference between modern-day humans is very small. There is on

average only a 0,1% difference – they share 99,9% of the same genes.
Between humans and apes there is a slightly larger genetic difference, but
they still share the large majority of their genes: between 96,9 and 98,8%
Studies show that, of the African apes, the chimpanzee is the closest relative of
humans. Chimps and humans share 98,8% of the same genes – there is a
1,2% difference (10 – 12 times larger than the difference between humans).
The analysis of mitochondrial DNA (mtDNA) and the differences that exist between
the mtDNA of two different species enables scientist to determine how long ago the
species separated. Based on such analysis, the following relationship diagram may
be drawn (see Figure 23 below)
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Figure 23: Diagram of relationships based on mtDNA comparisons
The study of genetics has proved invaluable in gaining a better understanding of

human evolution and of the origins of hominids. Given the amount of genetic
material shared between humans and other hominids (the apes), they must have
had a common ape-like ancestor who lived approximately 5 – 6 million years
ago.
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Cultural evidence
A very important aspect of human evolution, separating humans from

other hominids, is the development and use of tools.
Figure 24: A monkey using a stone to crack a nut; chimpanzee using a stick to
get at fruit in a box
The use of tools is not exclusive to humans, as illustrated in the images above.
(see Figure 24). Chimpanzees have been observed in the wild using simple tools,
e.g. using a piece of grass or a stick to fish for termites or, using a stone to crack
open nuts.
The manufacturing of tools is unique to humans – belonging to the genus Homo.

The type of tool, and the gradual development of more sophisticated tools, is
illustrated in the diagram below (Figure 25).
Oldowan tools (from Olduvai Gorge where these tools were first found).
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These are the earliest tools, from about 2,6 mya (million years ago), and
are associated with Homo habilis. They consisted of sharp flakes chipped
off a larger core – probably not sharp enough yet to cut raw meat.
Hand axe: These tools appear around 1,7 mya, and have been found at sites in
Kenya and South Africa. They are mostly associated with Homo erectus.
Flakes: About 250 000 years ago, early humans began to make smaller,
sharper, knife-like tools and scrapers. These tools, and all further
development, is associated with Homo sapiens.
About 40 – 50 000 years ago, longer blade-like tools appeared. About 20 000
years ago, humans began to make spears with stone (or bone) tips attached
to a shaft. They also made tools with microliths (small stone chips) fastened
to a shaft with animal sinew.
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About 5000 years ago, this stone industry came to an end, and was replaced by
copper, bronze, tin and eventually iron in tool-making.
Microliths / stone
tips in shafts
complexity
20 000 years ago

increasing
Longer blades 50
000 years ago
Levallois flakes
250 kya – early Homo sapiens
Hand axe
1,7 mya – Homo erectus
Oldowan tool
2,6 mya – Homo habilis
Time (years ago)
Figure 25: A brief history of early human tool making
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Two other aspects of culture had a significant impact on human evolution.
The first is the control of fire (being able to make a fire) to provide warmth, to
allow for the cooking of food, and contribute to social cohesion.
Art also contributed. The earliest known art dates from about 100 000 years
ago, and the earliest cave paintings (see Figure 26 below), of which we have
an abundance in South Africa, were made some 40 000 years ago.
The purpose of art? Some speculate that art bonded individuals, sustained
relationships for greater reproductive success, and was an attempt at
spiritual development.
449
Figure 26: San / !Kung rock paintings – the eland (right) was of
great spiritual significance to the San people and often featured in
their rites of passage
Activity 3: Fossil evidence
1.Explain why our understanding of the sequence of human evolution based on
fossil evidence might change in the future. (2)
2.The image below is of Mrs. Ples.
a) Name three ape-like features of this skull. (3)
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b) What clues are there in the image to the brain size of Mrs. Ples. (2)
c) Where was Mrs. Ples found, and by whom? (2)
What species did Mrs. Ples belong to, and when did this
species live? (2)
3. The species Mrs. Ples belonged to is extinct. What does this mean?
(1)
4. Which genus of early human lived on Earth for the longest time span? How
does this relate to the time span for the other two genera considered? (3)
5. Name three Australopithecine species that lived. For each species, give the
timeframe in which they lived, an example / specimen of the species, and
where, when and by whom the specimen were found. (12)
6. If asked to decide whether a complete skull with jaw-bones was that of

Ardipithecus or Australopithecus, what four features would you examine? (8)
451
1.Study the skulls shown in the image below.
a) Identify the species represented. Species include: H. habilis, A.
afarensis, A. robustus, H. sapiens, H. erectus. (5)
b) List four characteristics of the skull and brain size that you used to
make your selection. (4)
2. Draw a line graph to show the development of brain size from Ardipithecus
through to Homo sapiens. Use the following data.
Species Time frame (mya) Brain size (mL)
Ardipithecus ramidus 5 350
Australopithecus afarensis 3,4 460
A. afarensis 2,6 520

A. sediba 1,9 420
Homo habilis 2 650
H. erectus 1,2 950
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H. sapiens 0,2 1500
3. What conclusion/s can you draw from the graph? (8)
1. The diagram below shows possible relationships between members of the

family Hominidae. Study the diagram, then answer the questions that follow.
453
a) What is the name given to this type of diagram? (1)
b) How many genera, and how many species, are represented? (2)
Explain why A. robustus and A. boisei are more closely related than A.
boisei and A. afarensis. (2)

(57)
‘Out of Africa’ hypothesis
The ‘Out of Africa’ hypothesis states that all modern humans originated in
Africa, and then migrated out of Africa to the rest of the world.
454
Figure 27: Migration out of Africa into the rest of the world.
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Fossil sites in South Africa
There are many different fossil Hominid sites found in South Africa; but we will only
focus on the Cradle of Humankind.
The Cradle of humankind includes different sites (see Figure 29 below).

These sites have yielded more hominin fossils than any other site.
The Cradle of Humankind is situated in Gauteng Province, north-west of

Johannesburg which includes 15 different sites
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: Important fossil sites in South Africa
The discussion will only focus on 5 of the 15 sites:
Sterkfontein caves: First hominin discovery in 1936, and since then,

about 500 hominin fossils have been found there. This represents almost
40% of all hominin fossils found world-wide. Famous fossils:
o In 1947, Robert Broom (Figure 30) discovered Mrs Ples, the most
complete skull of the species Australopithecus africanus.
o In 1997, Ron Clarke (Figure 30), working with Stephen Motsumi and
Nkwane Molefe, discovered Little Foot, about 4,2 – 3,9 million years
old – the oldest fossil remains from the Cradle of Humankind.
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o In 2013, Lee Berger and his team excavated about 1550 fossils (at
least 15 individuals) of Homo naledi, a species of hominin not
known previously.
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Figure 30: Eminent SA palaeontologists (from left to right) –
Raymond Dart, Robert Broom, Ron Clarke.
Swartkrans – largest sample of Paranthropus robustus fossils anywhere,

with numerous homo fossils as well. The oldest fossils date from 2,1 – 1,9
mya.
Kromdraai – in 1938, the first discovery of Paranthropus robustus,

identified by Robert Broom. 29 hominin specimen, dated 2 – 1,8 mya
have been found there, with stone tools from around 1 mya.
Malapa – Karabo (Homo sediba), dated 2 mya – a transitional species

linking A. afarensis and the earliest form of the genus Homo.
Other sites: Drimolen, Plover’s Lake, and Gladysvale.
The importance of the Cradle of Humankind
The Cradle of Humankind is a world’s heritage site for these reasons:
Australopithecus africanus
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The first adult skull was found at Sterkfontein in 1936. A
virtually complete skeleton (Little Foot) was found there in 1997.
The fossils found at Sterkfontein are spread over a longer

timeframe than elsewhere (1 million years from 3 – 2 million years
ago). The species is only found in South Africa.
It is an early ancestor of the genus Homo.
Paranthropus robustus
Found at Kromdraai in 1938, and subsequently at Swartkrans. This

species has only been found in South Africa.
Lived in the same time period as Homo habilis, and fossils of these two
species have been found together at the Cradle of humankind. Could
this point to a speciation event occurring at the Cradle of Humankind?
460
Homo erectus
The first fossils were found by Robert Broom at Swartkrans. At

Sterkfontein, there is the first and only association of the Homo
erectus with early stone tools such as the hand axe.
Other South African sites
Taung (North-West Province): Taung child discovered here. It was the first
ever specimen of Australopithecus africanus, and suggested that hominin
originated not in Asia, as previously thought, but in Africa.
Makapansgat Valley (near Mokopane, Limpopo Province): Research at

Makapansgat was initiated by Raymond Dart in 1947.
Florisbad: In 1932, T. Dreyer discovered a reasonably complete skull, 260

000 years old, near Florisbad. The skull shows features linking it to both H.
heidelbergensis and to early Homo sapiens – probably a transitional fossil.
Other South Africa sites include the Border Cave in the Lebombo Mountains,
the Blombos Cave and the Klasies River Cave along the Cape coastline.
Other African fossil sites
The Great Rift Valley is a 2000 km long geological feature across Ethiopia, Kenya
and Tanzania. There are numerous fossil sites in the Rift Valley.
461
Figure 31: Location of the Rift Valley
in East Africa.
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Ethiopia (Hadar and Middle Awash)
In 1974, Donald Johansen discovered the first specimen of the

species Australopithecus afarensis at Hadar. Over 360 other skeletons
have been found there since.
Homo habilis fossils and Oldowan tools were also found there.
A large number of fossils of the species Ardipithecus ramidus was

found at Middle Awash in the Afar Depression in Ethiopia by Tim
White in 1994.
Kenya (Turkana and Omo)
The most complete skeleton of the Homo erectus (the Turkana boy,
dated 1,6 – 1,5 million years ago) was found at Turkana in 1984, by
Richard Leakey.
Richard also discovered the Omo fossils, remains of modern

Homo sapiens from about 195 000 years ago.
Tanzania (Olduvai Gorge and Laetoli)
Louis and Mary Leakey discovered fossils of Homo habilis (dated to

between 2,1 – 1,5 million years ago) here in 1960.
Mary Leakey discovered fossils – about 1,75 million years old – of

Paranthropus boisei (Nutcracker man) in 1959. In 1976, she found 3,5
million year old hominin footprints at Laetoli, evidence that our early
hominin ancestors walked with a bipedal, free-striding gait.
Activity 4: Out of Africa hypothesis
1. State the ‘Out of Africa’ hypothesis. (3)

2. Explain why we speak of an ‘Out of Africa’ hypothesis, not theory. (4)
3. What evidence is there to support the ‘Out of Africa’ hypothesis? (9)
4. What is mitochondrial DNA? (3)
What factors make mtDNA a useful tool in the exploration of human

evolution? (4)
In your own words, describe the importance of the Cradle of Humankind. (4)
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List two sites in South Africa, but not part of the Cradle of Humankind, where
important fossils remains were discovered. Provide some detail of the fossils
found. (4)
(31)
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Alternatives to evolution
Evolution is a well-established scientific theory based on real-world observation.
Nevertheless, various alternative explanation are proposed. These include:
Creationism
Creationists believe that all life was created individually by a supreme being using
supernatural powers. They do not believe that an existing species evolved from an
earlier species.
Intelligent Design
Proponents of intelligent design do not accept stages of natural selection since

nothing can evolve out of something simple to become more complex. The
complexity of things points to an intelligent cause.
Theistic Evolution
Theistic evolutionists believe in a divine being that created the material world through
the natural processes that we refer to as evolution. Evolution is simply the tool that
the supreme being uses to create the diversity and complexity of life around us. For
theists, science and religion can co-exist.
Literalism
Literalists interpret their scriptural texts literally. Christian literalists take the creation
accounts in the Book of Genesis literally. Literalists embrace a very narrow, more
restricted version of creationism.
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We will not be able to answer these questions unless we have an understanding and
knowledge of our evolutionary roots. Since the Darwinian revolution, we have come
to see ourselves as a result of several billion years of earth’s history rather than a
unique life form unrelated to other organisms on the planet. Like all other organisms,
we have evolved over time from earlier species, and share a genetic relationship to
all other forms of life on earth.
The study of human evolution involves understanding the similarities and differences
between humans and other species in their genetic make-up, body form, physiology
and behaviour.
Humans are mammals and members of the mammalian order known as primates.
The primate order
The order primates with its 300 or more species, is the third most diverse order of
mammals, after rodents and bats.
Primates can be divided into six subgroups: lemurs, lorises, tarsiers, New World
primates or Platyrrhini, Old World primates or Catarrhini, e.g. monkeys and baboons,
African apes (e.g. chimpanzee) and humans. Although there are some important
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differences between some primate groups, they share several anatomical and
functional characteristics showing their common ancestry, which had its beginning
about 85 million years ago.
Lemur
Tarsier
ape = any of the large, intelligent primates, including monkeys, chimpanzees,

gibbons and orangutans
A bit of trivia – primates and all their descendants lost the ability to make
Vitamin C which is why we as a primate have to include fruit and vegetables in our
diet. Other non-primate animals make their own.
What evidence is there that primates have a common ancestor?
There is biogeographical evidence of a common ancestor as all wild primates are

found in lands that previously were part of the southern continent, Gondwanaland. If
the latest research which indicates that primates originated about 85 mya is correct,
then continental drift, which broke up the super continent Gondwanaland (about 180
to 200 mya), probably played an important part in initial geographical subdivisions
within primates.
The common ancestor probably looked like a small-brained version of today's

dwarf lemur.
Map to show where old and new world primates are found
Most present-day primates are arboreal, i.e. living in trees; this characteristic
suggests that they evolved from an ancestor that was arboreal. This ancestral group
then diversified in arboreal habitats. Many, especially the new world monkeys of
South America, have remained totally arboreal while others have become at least
partly terrestrial, e.g. baboons (one of the old world primates).
Primates have many characteristics that are adaptations to this arboreal way of
life.
They have kept the clavicle or collarbone, which forms an important part of the
shoulder joint. Most other mammals have lost this bone.
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This bone helps to stabilize the shoulder, allowing a primate to support its weight by
hanging from its arms alone—something that few other mammals can do.
They have long, slender limbs that rotate freely at the shoulders and hips. This
helps their movement in the trees.
Many have mobile opposable thumbs. It is only the catarrhines (Old World
monkeys, apes, and humans) and a few of the lemurs and lories that have dextrous
hands. Note that it is only some of the new world primates that have a prehensile tail.
Hands with an opposable thumb and separate fingers are able to grasp and hold on
to branches effectively.
The following are other characteristics that all primates share:
an enlarged and complex brain relative to body size.
a flattened face and reduced snout with reduced sense of smell. This is possibly
because primates have come to rely on vision more than on smell.
eyes that face forward so that the eyes' visual fields overlap to give stereoscopic
vision. What is the value of this?
This feature is not limited to primates, but it is a general feature seen among
predators.
digits with flat nails. All other mammals have claws or hooves on their digits. Nails
probably allowed for manipulation that is more sensitive.
molar and premolar teeth with cusps that are low and rounded. Other placental
mammals have high, pointed cusps or elaborate ridges. This distinction makes
fossilized primate teeth easy to recognize.
complex social behaviour, usually only one offspring at a time and extended
care for the young.
Genetic evidence of a common ancestor for primates is slowly emerging.

Primates:
share a large percentage of their DNA. It is well known that humans share about
98.5% of their DNA with chimpanzees and 93% with rhesus monkeys. This suggests
that they must have had a common ancestor at some stage.
have a larger number of olfactory-receptor pseudo-genes than non-primates.

This is consistent with the deterioration of the sense of smell in primates. Humans
have about 60% and non-human apes 30% more pseudo-genes than non-primate
mammals.
pseudo-genes = remnants of genes that are no longer functional
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have full trichromatic colour vision (ability to perceive red, green, and blue),
which is found only in the primate order, e.g. humans, apes and old world
primates. These primates all have the same opsin genes that provide this type of
vision.
This topic could become a favourite of the examiners.
Learning activity 1
Evidence of a common primate ancestor
1.What biogeographical evidence suggests that primates have a common ancestor?

(2)
2.Complete the following table to show the arboreal features that primates have in
common. In the blank space devise very simple diagrams to show the value of these
to the early primates. (3 + 3)
Arboreal Value to early primates (diagrams)

characteristic
3.Devise a simple, clear learning diagram to show features, other than arboreal, that
all primates share. Number the features but use no words. (9 x 2)
Total [26]
Sequence of human evolution
Humans belong to the order primates, which is divided into two super families.
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Prosimians (meaning ‘before apes’), e.g. the bush baby (Lesser Galago) of
southern Africa.
Hominoidea (great apes), which typically have large brains when compared to body
size. Monkeys, African apes (bonobo, gorillas and chimpanzee)
and humans belong to this family. The hominoidea group gave rise to
the hominidae family. This in turn gave rise to two subfamilies, the homininae and
ponginae.
Due to differing characteristics, homininae has been further divided into two tribes.
Gorillini (gorillas)
Hominini – Hominins (living humans and their extinct ancestors) and Pan
(chimpanzee and bonobos)
Phylogenetic tree with the hominidae (grey box) as the ancestral family
Genetic analysis combined with fossil evidence indicates that:
Hominidae family split (speciated) into the subfamilies, homininae and ponginae
about 15 mya.
Homininae subfamily split into two tribes, hominini and gorillini about 7.5 mya
Hominini tribe split into the genera, Homo, australopithecines and Pan about 6 mya.
The above information is roughly shown in the phylogenetic tree below. Speciation
times vary in different reference sites.
Phylogenetic tree showing the relationship between primates
How do the hominidae relate to other animals?
A phylogenetic tree depicts a hypothesis about evolutionary relationships among

organisms.
The phylogenetic tree on the next page illustrates the evolutionary relationship of
hominidae (also known as great apes) among other vertebrate animals. The tree is
based upon similarities and differences in their physical or genetic characteristics.
As can be seen on this tree hominidae branched off from their closest vertebrate
relative a very long time ago, 85 to 65 mya (A). These were the early mammals and
the extant reptiles and birds, and the extinct reptiles. This time period, 85 to 65 mya,
is when the primate order arose.
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The cut-off lines indicate vertebrates that became extinct.
It is worth noting that modern humans and extinct anthropoids are genetically very
closely linked.
Phylogenetic tree to show the evolutionary relationship of hominidae and

other vertebrates
Evidence for a common ancestor for living hominids
Living hominids include the African apes and humans. Why do we want to show that
hominids have a common ancestor? If there is a common ancestor we will be able
to trace the evolution of humans from this ancestor through the series of early
hominin species to today's humans.
To try and find the common ancestor, scientists use the fossil record and genetics
(chromosomal DNA and mitochondrial DNA). The common ancestor should have
traits that are found in both African apes and humans. Knowing the similarities and
differences of African apes and humans will give us a starting point when looking
at fossils of early man and enable us to follow the trend in human evolution. This is
done below. Much of this information will be repeated later.
African apes and humans – compared
Physical and genetic similarities show that the modern human species, Homo
sapiens, very closely resembles the African apes, i.e. chimpanzee, bonobos and
gorillas.
However, it must be stressed that humans did not evolve from African apes. Rather
the two groups evolved from a common ancestor. Based on the estimated rates of
genetic change, this common ancestor is thought to have existed about 6 million
years ago. After splitting into two lineages, one that led to the chimpanzee (an
African ape) and the other to humans both species have undergone 6 million years
of separate evolution.
Chimpanzee (Pan troglodytes)
What are their anatomical similarities?
All living hominins:
have an upright posture
lack external tails.
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have freely rotating arms
have hands with an opposable thumb that, with the other fingers, allows them grasp
and handle objects. The thumb sticks out sideways.
have digits (fingers and toes) with flat nails. All other mammals have claws or hooves
on their digits. Nails probably allowed for manipulation that is more sensitive.
have eyes that face forward so that the eyes’ visual fields overlap to give
stereoscopic vision. What is the value of this? This feature is a general feature of all
predators.
have molar and premolar teeth with low and rounded cusps. Other placental
mammals have high cusps. Look at those of a cat or dog. Where fossil teeth are
found, this feature makes it very easy to identify the fossil as a hominin or not.
have eyes with cones for colour vision.
are sexually dimorphic (male and female vary in some physical trait), e.g. males are
about 5 to 10% larger and have an upper body with larger muscles.
have a large brain compared to body mass.
What are their anatomical differences?
As mentioned before humans and African apes have been evolving separately for
about 6 million years. During that time, humans experienced different selection
pressures, such as climate change, different diet and effect of bipedal locomotion.
These different pressures resulted in various physical differences developing.
It is the physical differences that one must be aware of when looking at hominin
fossils. They will help trace the evolution of humans.
Skeletal differences
The anatomical differences between humans and African apes are largely related to
the evolution of habitual bipedalism in humans. The African apes are tree
climbers, but when on the ground, they are quadrupedal knuckle-walkers. Apes can,
however, walk briefly on two legs but humans do so habitually.
bipedalism = ability to walk upright on two legs
Habitual bipedalism is the most important adaptation that started humans on their
evolutionary path. It has resulted in many differences between the skeletons of
humans and the African apes.
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Skeletons of African ape and human
Apes have:
arms that are usually longer than the legs.
fingers and toes that are long and curved for grasping branches.
big toes that are divergent.
ilia (hipbones) that are large, elongated and parallel to the spinal column. This is to
support the legs and trunk in the bent-over posture necessary for quadrupedal
knuckle-walking.
a bow-shaped (less curved) spine.
Humans have:
arms that are shorter and weaker than the legs. If long arms were no longer needed
for climbing they would not have been selected.
fingers and toes that are short and straight.
thumbs that can grasp objects precisely and firmly between the tips of the fingers
and thumb.
This has greatly increased humans ability to manipulate objects. The African apes do
not have this advanced manipulating ability. They can only grasp between the thumb
and sides of the other fingers.
a shorter, broader and more bowl shaped pelvis, which supports the legs and trunk
in an upright position. Thus provides greater stability for walking and running. See
alongside and below.
longer femurs (thighbones) that are set farther apart at the hips than they are at the
knees and slant toward the midline to keep the knees close together. This angle
allows anthropologists to diagnose bipedalism even if the fossil is only the knee end
of a femur.
The femur arrangement makes walking and running more efficient.
From L to R, hip bones and femur of chimpanzee, early human and modern
human
Notice in the two humans how the femur increases in length and slants towards
midline, and how the pelvis changes in shape in all of these hominids.
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feet that have:
–a large strong heel.
–tiny toes with the large big toe moved into line with the others, i.e. convergent.
–longer feet with a stable arch, which supports the body better. An African ape’s foot
is mobile.The human foot is adapted to support the whole weight of the body and for
walking or running.
a spine curvature that has two major curves, the thoracic (where the back curves
away from the chest) and the lumbar (where the spine curves towards the stomach).
These S-shaped curves keep the trunk of the body, and the weight of it, centred
above the pelvis, which is crucial for efficient upright walking.
Brain differences
Humans have a much larger brain than that of the African ape, especially the
cerebral cortex. The average capacity of an adult chimpanzee brain is 395 cc while
that of a modern human brain is 1 350 cc. Humans have relatively far more white
matter in the cortex than chimpanzees. This means that there are more connections
between nerve cells and therefore a greater ability to process information.
Comparative brain sizes of human (top) and chimpanzee (bottom)
The larger more complex brain is responsible for the development of the unique
behavioural qualities of humans, which include:
using their hands with greater dexterity to make simple tools. After bipedalism, tool-
making was the next major evolutionary step in human development.
the use and control of fire.
the use of a highly developed language.
Skull differences
Humans do not have the pronounced brow ridges of an African ape. See next
column.
The foramen magnum in humans is found centrally under the skull, unlike apes that
have it at the rear of the skull.
Therefore the spine of a human connects with the skull underneath and near the
centre so that the head is held firmly upright and the body's centre of gravity is
directly over the legs. This reduces the energy needed to balance.
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To show spine and skull connection of human and African ape
However, the spine of an African ape connects with the skull at the back to allow
for the attachment of strong neck muscles and to place the head at an angle; the
proper position for walking on all fours.
Humans have a large braincase, small jaws, a nearly vertical face and chin, but
African apes have a small braincase, large jaws, a sloping face but no chin. See
below and alongside.
These features suggest that the cranial capacity of the African apes is smaller than
of humans and that their diet is different.
The canine teeth of humans are relatively small, whereas those of apes are large
and pointed and project beyond the other teeth.
Humman skull
Chimpanzee skull
Learning activity 2
African ape and human comparison
Question 1
1.Using simple diagrams complete the table:
physical features that African apes and humans share. (6)
value of the features to each species. (6) [12]
Common features Value to apes and humans (diagrams)
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2.Devise a simple, clear learning diagram or diagrams to show the physical
differences between African apes and humans. Number the differences but
use no words. [20]
Question 2
1.Which hominid was bipedal, A or B? (1) ____
2.Mention two features in A or B that indicate bipedalism. (2)
3.Which leg, C or D, belongs to a human? (1) ____
4.Mention two features that indicated the leg mentioned in Question 1 is from a
bipedal animal and give the advantage of each. (2 x 2=4)
5.Name a living hominid that could have a leg like that in the alternative illustration.
(1)
6.Which foot, E or F, is from a bipedal animal? Name two anatomical features it has
for bipedalism. (3)
7.Explain why the other foot is structured as it is. (3)
8.1The limbs of the two hominids have similar characteristics that show they are a
product of descent from a common ancestor rather than a product of a similar
environment. What is the term for such characteristics? (2)
8.2What is the term used for the make-up (plan) of the limbs of all vertebrates? (1)
[18]
Total [50]
Human evolution from ape-like ancestors
What is the evidence?
The story of human evolution began in Africa about 6 million years ago and where it
continued until about 2 million years ago. The forces of natural selection have
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directed it. Environmental factors such as climate change causing alterations in
habitat and food supply, as well as fast-running prey and fierce predators, acted on
the gene pool.
Those hominins with adaptations that allowed them to survive to breed successfully
over time formed new species.
For much of the first 4 million years there were more than one hominin species living
in Africa at the same time. Over time, with the exception of the human
species, Homo sapiens, they all became extinct.
The main sources of evidence to show humans have evolved from an ape-like
ancestor are:
A.Fossil evidence, i.e. the fossil record of early hominins
B.Genetic evidence, specifically analysis of mitochondrial DNA (mtDNA)
C.Cultural evidence such as tool-making
A. Fossil evidence
A large number, approximately seven thousand, hominin fossils have been found
worldwide. These represent about 6 million years of evolution.
The most common fossils are teeth and lower jaws, and the facial and upper cranial
bones of the skull. Skulls are almost never found intact but can be reconstructed
from fragments. Femurs are the next most common, while remains of the feet,
hands, pelvis or spine are very rare. In a later section you will find out why the
hominin fossil finds in South Africa are so remarkable.
By studying fossilised bones, scientists learn about the physical appearance for
example of earlier hominins and how they changed over time. Bone size, shape and
markings left by muscles show how hominins moved around and held tools.
Although the hominin fossil record is far from complete, there is enough evidence to
give a good outline of the evolutionary history of Homo sapiens, i.e. humans. To try
and work this out, palaeontologists look at the following key features of the fossils:
Bipedalism (spine and pelvic girdle)

Brain size
Teeth (dentition)
Prognathism (having a jaw that sticks out markedly)
Palate shape (roof of mouth)
Cranial (sagittal) and brow ridges
Bipedalism (spine and pelvic girdle)
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As mentioned earlier habitual bipedalism, walking upright was the most important
adaptation that started humans on their evolutionary path. It is therefore very
important to be able to trace the gradual transition from walking on four legs to
walking on two legs.
Some of the early hominids (hominins and African apes) were probably pre-adapted
to bipedalism; they had freed arms that they used for climbing trees and stretching
for fruit. About ten million years ago, when the climate changed and Africa was
drying up, the habitat changed from near continuous forest to wooded savannah.
This had great consequences for human evolution as our ancestors would have
been forced to move partially upright across open ground to find new sources of
food. With time those early hominids that could successfully move about upright on
the ground survived to breed and in time formed a new species.
Natural selection in action!
Bipedalism, therefore, gave them a crucial advantage in the struggle for survival. It
enabled early hominins to:
live in a greater variety of areas, e.g. forested areas, open savannah, deserts and
coastal areas.
see danger from predators.
gather food and make and use tools with their completely free arms and more erect
stance.
reduce the risk of over-heating as a large surface area is exposed for losing heat to
the surroundings.
Bipedals only need two shoes.

Therefore saves shoe leather.
What are the disadvantages of bipedalism?
The backbone no longer acts like a cantilever bridge between the hind and
forelimbs and is put under a lot of stress. How many of you have parents that
suffer from backache?
Bipedalism removes the shock-absorber function of the shoulder blade that

front-legged animals benefit from when they take a leap. The reshaping of the
pelvis narrows the birth canal, so children are born when they are smaller and
relatively helpless. Discuss whether this premature birth was an advantage or
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disadvantage in hominin evolution. Perhaps it compelled more parental care and
opened opportunities for learning from parents during the long childhood.
How do we know if a fossil was bipedal?
Generally, palaeontologists decide if a fossil hominin was bipedal by looking for the
following:
a foramen magnum that is positioned further forward; the skull weight is born by
the shoulders while walking upright with the skull balanced on a vertical spine. See
the diagram below that shows the spinal column vertical and directly under the head.
Position of foramen magnum in an ape, early hominin and Homo sapiens
Under-surface of hominid skulls
Foramen magnum is positioned:
near the back of the skull in apes (left)
under the skull in humans (right)
in intermediate position in fossil hominids (two middle)
a shorter, broader pelvis; allows for efficient weight distribution in an upright

position. See page 262.
an S-shaped spine; this acts like a spring enabling an upright posture to be easily
maintained. See page 261.
Learning activity 3
Bipedalism
1.Why has it been suggested that hominins were pre-adapted for bipedalism? (1)
2.What ecological change took place that caused these early hominins to start
leaving their natural habitat, the forests? (2)
3.What was the possible selection pressure that allowed habitual bipedalism to
evolve by natural selection? (1)
4.In ape-like beings mention three features that indicated they were bipedal? (3)
5.Devise a learning diagram to show three features of a fossil spine and pelvic girdle
that show evidence of bipedalism. (3)
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Total [10]
Brain size
Throughout human evolution there were drastic climate changes. This caused the
environment to alter and be unpredictable. To enable our ancestors to survive, a
larger, more complex brain, capable of processing new information, was selected.
This trend of an increase in braincase size (and bigger brain) over time can be
observed in fossils. See the series of skulls below.
The average brain capacity of African apes (395 cc) is close to that of very early
hominins (435 cc). Brain size continued to increase in the later hominins (700 cc
then 850 cc), and finally Homo sapiens (1 350 c).
Cranial capacity increase from very early to latest hominin, i.e. modern man
Note:
The larger brain made the following possible:
better co-ordination of movement.
large amount of information could be processed.
the development of speech and ultimately a written language for communication.
Teeth (dentition)
Fossil teeth are important as they give an indication of which specific hominin
species one is looking at, what they ate, and in what type of environment they might
have lived.
The tooth remains show a general decrease in size, particularly of molars and
canines, through the ages. There is an exception, Paranthropus robutus that had
massive grinding teeth (molars and premolars) in its large lower jaw when compared
to the incisors and canines. This would indicate that its diet probably would have
been mostly coarse, tough food that needed a lot of chewing.
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The tooth enamel, thin in African apes, gradually thickens in early and later hominins
until in humans it is thick.
In African apes and early hominins the canines are larger and project above the
tooth row. Over time they gradually have got smaller until in humans they are the
same size as the other teeth and no longer stick above the others.
The canines of the African apes are so large that a gap (the diastema) develops
between the canine and incisors to make room for the opposing canine so the jaw
can close. In early hominins this can still be seen. However, in the later hominins it
disappeared.
Learning activity 4
Hominid dentition
By making a series of simple diagrams, show the changes in hominid teeth from
African apes through early hominins and finally to humans.
Prognathism
African apes have large and prognathous jaws, i.e. jaw sticks out beyond the upper
part of the face.
This condition is still seen in the early hominins, the Australopithecines. Partly
because the teeth and the muscles for chewing become smaller the trend is towards
a smaller and less sloping face until finally in humans the face is small and flat.
L to R – Prognathism of an African ape, an Australopithecine, H.

erectus and H. sapiens
Palate shape
The palate, sometimes called the dental arch, is the bone separating the mouth and
nasal cavities.
The chewing trend is away from crushing and tearing to crushing and grinding. For
this to happen, the palate shape changed from a roughly rectangular palate in
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African apes to u-shaped in early hominins (australopithecine) and finally, in Homo
sapiens, to a parabolic curve. Notice the diastema on the chimpanzee and
australopithecine palate.
Palate shapes, L to R, of a chimpanzee, an australopithecine and H. sapiens
Cranial and brow ridges
Cranial ridge (sagittal crest), found on the top of the skull, can be seen in hominids
that have protruding (prognathous) jaws and well-developed chewing muscles, e.g.
gorillas.
Skull of a gorilla
The photograph below of a Paranthropus robustus (an early hominin) skull has a
sagittal crest. This indicates that the chewing muscles were powerfully developed. In
later hominins the ridge is absent.
Skull of an early hominin (Paranthropus robustus)
Brow ridges, i.e. bony ridges over the eye sockets, are very big in African apes (see
the gorilla skull alongside) and are also well developed in some early hominins. They
get smaller in later hominins until in humans they are greatly reduced or usually
absent. They may have served as buttresses against the stress exerted by jaw
muscles or as protection for the eyes.
Skull of Homo ergaster showing brow ridges
How does the change in teeth and skull show a change in diet?
Another trend evident in human evolution is the change in diet from raw food to
cooked food. The first and most important trend was bipedalism followed by tool-
making.
The following suggests that the ape-like beings ate raw food, plant matter and meat,
which required a great deal of processing, i.e. tearing, biting and chewing.
The teeth, especially the canines, were larger.
Jaws were large and protruding.
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Cranial and brow ridges served as attachment for large chewing muscles.
Early Homo species used tools to cut and grind food before eating. Therefore, large
teeth became unnecessary. In addition the later hominin species (H. ergaster,
erectus, heidelbergensis and sapiens) began to cook their food, which meant that it
did not need the same amount of processing. Teeth were needed to only bite and
crush food. This is seen by:
smaller teeth, including the canines.
smaller jaws and a less prognathous skull.
the absence of cranial and brow ridges, which were not needed for muscle
attachment, as the muscles for chewing were much smaller.
Therefore the reduction in cranial and brow ridges, jaw size and tooth size show a
change in diet from raw to cooked food.
Learning activity 5
Difference between African apes and humans
You can now consolidate the differences between African apes and humans by
completing the following table.
Characteristic Feature African apes Humans
1._____________ 2._____________ back of skull centrally placed
Spine single bow- 3._____________

shaped curve
Pelvic girdle 4._____________ short and wide
Big toe Divergent 5._____________
Brain size 6._____________ larger, more

developed
Head cranium flatter 7._____________
Chin poorly developed 8._____________
Skull ridges Cranial ridge pronounced absent
9._____________ pronounced usually absent
Teeth Space between 10._____________ no space
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teeth (diastema)
11._____________ large smaller
Palate shape 12._____________ 13._____________
14._____________ Jaws more protruding less protruding
Face 15._____________ 16._____________
Forehead slopes backwards 17._____________
Total [17]
B. Genetic evidence
The strong similarities between humans and the African great apes led Charles
Darwin in 1871 to predict that Africa was the likely place where the common
ancestor of African apes and humans came from. As will be explained, both
chromosomal DNA and mitochondrial DNA (mtDNA) evidence supports this daring
prediction made almost 150 years ago, as do the fossils.
The comparison of nuclear DNA (or genes) of two hominoids shows how
related they are. The more genes they share the more closely they are related.
–All humans share about 99.9% of the same genes, showing their obvious close
relationship.
–Humans and apes share between 96.9% and 98.8% of the same genes.
–Of the apes, the chimpanzee (African ape) shares the most genes with humans
(98.8%), making them the closest relative to humans.
This close relationship shows that humans and apes must not only have had a
common ancestor, but that this ancestor must have been ape-like.
Comparison of hominid mtDNA shows how long agohumans and African apes
shared a common ancestor.
The number of differences in the mtDNA of two species tells scientists not only how
related the species are but how long ago they separated. If there are few
differences, the species separated recently. If there are many differences, the
species separated long ago.
A cladogram based on a comparison of mtDNA of living hominids, Asian and

African apes, and humans
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The preceding cladogram shows that the common ancestors for all apes and
humans lived about 15 mya, and the common ancestor of humans and chimpanzees
lived about 6 mya. From that common ancestor, African apes and hominins diverged
along two separate lineages.
For practical reasons the cladogram was drawn up using mtDNA from living
hominids as after death, DNA starts degrading immediately so no or very little DNA
is available from fossils
To sum up:
Genetics are proving invaluable in gaining a better understanding of human

evolution. Geneticist can:
by comparing the nuclear DNA of hominids see how related they are.
by comparing the mtDNA of hominids show:
–that humans evolved from ape-like ancestors.
–the approximate age when the evolutionary paths of the various hominids diverged.
Learning activity 6
Evidence from genetics that humans
evolved from ape-like ancestor
1.The table below shows a comparison of the DNA differences between members of
the hominoid family. Study it and answer the questions that follow. Do you remember
that hominoids include humans, apes and monkeys?
Hominoid family DNA

differences
Human and human 0.1%
Human and chimp (African ape) 1.2%
Human and gorilla (African ape) 1.6%
Human and orangutan (Asian ape) 3.1%
Hominid and monkey 7%
1.1Which African ape has the most similar DNA to us? (1)
1.2What percentage of our genes do we share with the chimpanzees? (1)
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1.3What information in the table suggests that we are more closely related to African
apes than we are to monkeys? (1)
2.By referring to the cladogram, on the previous page, answer the following
questions.
2.1What information was used to draw up this cladogram? (1)
2.2According to this cladogram how long ago did the common ancestor of
chimpanzees and humans live? (1)
2.3Which hominids fall under the grouping of ‘African apes’? (1)
2.4Which species is most closely related to the chimpanzees? (1)
2.5Which of the hominids is most distantly related to humans? (1)
Total [8]
C. Cultural evidence
Fossils and genetic evidence are not the only evidence of human evolution. Early
hominins very gradually began to control their environment; to use it to alter their
way of life because of the unique combination of:
a larger brain, especially the cortical area.
specialised physical features such as more dexterous hands.
This non-genetic means of adaptation, called cultural evolution, improved the

success of early hominins.
Tool-making
African apes use objects such a stones (to crack nuts) and thin sticks (to pull
termites out of termite mounds). This behaviour is learnt from their parents and it is
likely that the common ancestor of chimpanzees and humans used tools similarly.
However, they did not make tools. Therefore, the remains of manufactured tools are
evidence of human cultural evolution.
After the evolution of bipedalism (4.2 mya) in the earliest genus of

hominins, Ardipithecus, tool-making was the next major step in human evolution.
It marks the first trait that is unique to the genus Homo. Hominin hands are well
adapted for tool-making as they are capable of fine manipulation and coordination.
Tool-making (modification of rocks and later bone, metals, wood, etc.) and the use of
the tools lead to:
new ways of getting food, e.g. the ability to crack open long bones and get at the
marrow, to dig and to sharpen or shape wooden implements.
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efficient hunting in organised groups with the later more sophisticated tools.
Hunting also required the development of good communication.
Gradually as the learned skills and behaviours were passed on to offspring

cultural evolution occurred.
By dating stone tools, a clear pattern of tool evolution can be seen. The earliest
tools were large, simple and crude while the most recent were small, complex and
elegant. See below. Put simply, much less skill was needed to make the early tools
than the later tools. The greater the evidence of skill the more the brain, particularly
the cerebral cortex and thus the species, must have evolved.
Homo habilis Homo ergaster, Homo Homo sapiens

erectus
chopper and flakes hand-axe blade, point and scraper
Simple core and Tools shaped on both sides Small tools, part of tool
flakes kits
2.5 2.0 1.5 1.0 0.5 0.25 0.01 mya
Stone tool evolution
1. Beginning 2.5 mya to 0.2 mya – very static over a very long period of time
The first evidence of the intentional manufacture of any stone-tool comes 2.5 mya
from the Ethiopian Rift Valley. The early humans, probably Homo habilis, used
hammerstones to strike stone cores and produce sharp flakes. These large simple
tools represent the simplest form of stone tool technology and are known as
Oldowan tools. They show little if any control over the end design. None-the-less
they are evidence that the early humans had intellectually evolved beyond their
earlier hominin ancestors, the australopithecines, who did not appear to make
tools. Paranthropus robustus might have made bone tools for gathering plant foods.
For more than 2 million years, early humans used these tools to cut, pound, crush
and access new foods—including meat from large animals.
There were two groups of tools.
Choppers (the remains of the core), which were for crushing nuts and seeds, or
bones to get the marrow and for softening vegetable material.
Scrapers (the flakes chipped off the core), which being sharp could cut the meat off a
carcass killed by other animals.
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These unsophisticated tools suggest that the early Homo species, Homo habilis,
were scavengers and not hunters.
The most basic of all tools, an Oldowan stone tool chopper with a simple edge,
and scrapers
2. From 1.5 mya until about 250 kya – basically static
At about the same time as Homo ergaster appeared archaeologists found that there
was a major change in the stone-tool industry.
These more advanced tools of the Archeulian industry showed a preconceived

design, not just a random hammering of a core stone. This provides evidence of the
intellectual evolution of their probable makers, H. ergaster. These large tools had a
central core of a stone with larger flakes chipped off and edges that were sharpened
all round and had a more regular ‘tear-drop’ shape. For well over a million years
these double-faced hand-axes, cleavers and picks (collectively known as bifaces)
were made and used. During this time they showed little variation.
With these multi-purpose sharper tools H. ergaster became an efficient hunter of

small mammals, and was able to live on a mixed diet of meat and plants.
Hand-axes made by Homo ergaster
3. Beginning 250 kya to recent times – not static, pieces of art
The Acheulian tool industry ended only about 250 000 years ago, which may be
associated with the rise of Homo heidelbergensis (archaic Homo sapiens).
Technological and cultural evolution really accelerated from about 250 kya. The
stone tools became more diverse, smaller and more refined, e.g. knives,
scrapers, slicers and needles. Some tools had engravings with symbolic markings.
These changes required thoughtful actions, fine motor control and co-ordination, all
of which showed further cultural evolution.
Elegant stone flake tools
Bone tools dated to about 80 000 years ago have been found in Blombos Cave, on
the southern Cape coast of South Africa. Showing more cultural evolution.
By about 40 000 years ago, humans had learned to craft small flakes and blades that
became part of a lightweight, sophisticated composite toolkit. The tools were
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used for an even greater variety of specific tasks, e.g. micro-blades and other points
were probably hafted on to shafts to make spears, darts and arrows, which allowed
the hominins to catch fast and dangerous prey. All of this is further evidence of
hominin evolution.
Stone spear
About 20 000 years ago the development of a far more complex tool kit,
with microliths, bone and wooden tools with an infinite variety of uses, from
stitching to harpooning fish, was further evidence of the evolution of modern human
behaviour. These later tools were also things of beauty, something not seen in
earlier tool cultures, which showed an aesthetic appreciation – a human trait.
Microliths
About 5 000 years ago stone was replaced by copper, bronze and tin in tool-making
as more complex societies evolved.
Other indications of cultural evolution
There are other practices that showed the cultural evolution of hominins. These
include the following.
Co-operative hunting, which enabledearly hunters to catch large prey that

otherwise would not have been possible.
Fire-making, this provided a means of keeping warm, deterred predators from the
camp site and helped drive prey during a hunt. During the evenings, fires probably
also encouraged socialization. All signs of cultural evolution.
What can the use of fires tell us about the lifestyle of H. erectus?
The control and use of fire is highly significant as it enables anthropologists to

determine a fair amount about the lifestyle of the early hominins – H. erectus / H.
ergaster (African H. erectus).
Fire could have:
led to social behaviour with the warmth and extended ‘daylight’ hours.
encouraged conversation and teaching.
offered more permanent (but still temporary) dwelling sites.
given a measure of protection from predators at night.
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helped in co-operative hunting by herding animals away from fire.
provided humans with roast meat making it more appetizing. This could have
resulted in more protein being eaten, which may have aided brain development.
a wider choice of food, including smoked and dried fish and meat, and led to the
invention of cooking.
been a sign of intelligence, as keeping a fire going showed forward planning.
enabled better, stronger tools to be made that would have led to more successful
hunting.
been a factor that enabled H. erectus to migrate out of Africa and into colder climates
in Europe and Asia.
The controlled use of fire marked a crucial change in human behaviour as it showed
they had the ability to adjust the environment to suit their needs.
About 5 000 years ago stone was replaced by copper, bronze and tin for tool-
making
Learning activity 7
Stone technologies in Africa
1.Do you think the common ancestor of chimpanzees and humans could make stone
tools? Give a reason for your answer. (2)
2.By completing this table the rather complex history of stone technologies should
become simpler for you. Remind yourselves that the type of diet of early Homo was
changing along with the evolution of these tools; from fruit and nut eating, to
scavenging and finally to hunting. Also remember that it was an enlarged brain that
allowed these hominins to make the more sophisticated tools. Enjoy! (3 + 3 + 6 + 3 =
15)
Time range of tool First hominin Types of Simple diagram(s)

use to use tools (6) of
(3) tool (3) tool(s) (3)
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3.Describe the broad uses and changes in type of tools made by Paranthropus
robustus, Homo habilis, Homo ergaster and Homo sapiens (humans). (4 x 2 = 8)
Total [25]
Major phases in hominin evolution from 6 mya to the present
The first 4 million years or so of human evolutionary history took place exclusively on
the African continent. Over the passage of time, from the common ancestor of the
hominids to modern humans there have been jumps in human evolution. What
caused these? A current hypothesis is that extreme shifts of climate where it swung
wildly from hot and wet to dry and cold were a key factor in driving human evolution.
These dramatic changes presented powerful selection pressures for all living
organisms. Many plants and animals became extinct. However, hominins survived
mainly as nature selected for survival those variants with the ability to walk
upright and with larger brains. These hominins being more intelligent and
physically adaptable could deal with different environments and changing food
sources. The successful hominins then bred to form populations of new species.
The Tribe Hominini (humans and fossil hominins) and the African apes separated
about 6 mya in Africa. By comparison, dinosaurs died out 65 mya, the earth was
formed about 4 6oo mya and the universe was born about 14 ooo mya.
So, that does make us relative newcomers to planet earth, doesn’t it?
What are the genera of Tribe Hominini?
A.Orrorin and Ardipithecus – the earliest hominins, from Ethiopia
B.Australopithecus, from East and South Africa
C.Homo, from various sites in and out of Africa
All members of the hominini tribe walked habitually on two legs, i.e. they were (or still
are) bipedal.
When tracing the changes over time, one will see a great transition from an
arboreal, long-armed, short-legged, small-brained creature to a terrestrial one with
short arms, long legs and a big brain.
Within these genera there are 15 to 20 different species of early hominins. There is
not agreement on how these species are related but there is only one living hominin
species, i.e. us humans, H. sapiens.
The large amount of fossil evidence shows that:
humans were preceded for millions of years by other hominins.
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at times many hominin species co-existed. See time-line graph below.
there was no ladder-like progression in which one species gave rise to the next.
Time line graph (or phylogenetic tree) to show one interpretation of the origin
of humans
Drawings to show the different species and relative sizes of the hominini tribe
Note: In the following information about hominins, under the sub-

sections ‘Diagnostic features’, both physical and behavioural features of each
example are given.
A. Ardipithecus
In this genus bipedalism is evident. Bipedalism is the earliest major trait of

hominins and the single most important difference between humans and apes.
Ardipithecus ramidus (5.8 to 4.4 mya)
Ardipithecus ramidus is one of the earliest examples of what one would expect the
most recent common ancestor of humans and African apes to be like. It lived in
North-East Ethiopia.
Diagnostic features – Ardipithecus
Height is 1.2 m high, weight about 50 kg.
Brain case is small (350 cc).
Arms and fingers long. Similar to African apes.
Foramen magnum more forward than apes therefore could walk upright. Divergent
big toe helped grasp branches therefore could move through trees.
Skull has brow ridges and lower face projects.
Has ape-like teeth but molars are smaller and narrower and canines reduced.
Skeleton of Ardipithecus ramidus
Well known example
‘Ardi’ (4.4 mya) – an almost complete female skeleton
B. ‘Australopithecines (4 mya to 1 mya)

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Between 4 and 1 million years ago, several different species of ape-men, the
australopithecines, inhabited the African landscape – in the Rift Valley (Ethiopia,
Kenya and Tanzania) and in South Africa. While there was much variation in
different areas two dominant australopithecine forms emerged, probably as a result
of habitat and dietary changes.
A gracile (thin/slender) form, with smaller teeth and chewing muscles, is likely to
have led to the first humans. Examples of these were Australopithecus
africanus and Au. sediba.
Skull of Australopithecus africanus
A robust form, with very large jaws and teeth, which became extinct about 1 million
years ago. It is now more commonly placed in the
genus Paranthropus. Paranthropus (Australopithecus) robustus is a well-known
example of this form.
Skull of Paranthropus robustus
Diagnostic features – australopithecines
Quite short (1 m – 1.5 m) and upright.
Face strongly projecting (prognathic), low sloping forehead, large brow ridges,
sometimes cranial ridges, no chin.
Palate is u-shaped. The trend is for a reduction in canine size in later

australopithecines and the disappearance of the diastema.
Brain capacity is small, 435 cc to 530 cc.
Walked bipedally – main way of moving.
Position of foramen magnum (more forward), human-like pelvis and leg and foot
bones confirm this.
Arms long and strong, hands curved, legs relatively short, feet short with long toes.
All suggest they still climbed trees.
Probably omnivores, scavenging food from carcasses killed by lions and other
predators and feeding off fruits and leaves. Why do you think they scavenged rather
than hunted? And, why would meat-eating be important in the evolution of hominins?
Examples of australopithecines
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1. Australopithecus afarensis (4.0 – 3.0 mya)
Australopithecus afarensis is key species in human evolution as it had both ape and
human characteristics and is probably ancestral to the Homo genus. They are one of
the best understood of the early hominins as hundreds of fossils from dozens of
individuals have been found. Their adaptations for living both in the trees and on the
ground helped them survive for almost a million years as the climate and
environments changed. They lived for over four times as long as our own species
has been around.
Diagnostic features – Australopithecus afarensis
Short, about 1.0 – 1.5 m tall.
Small cranial capacity (435 cc), about 1/3 that of a modern human brain.
Light build, long arms, curved fingers and toes.
Ape-like features – skull has low forehead, brow ridge, flat nose, sloping face, no
chin.
Dentition primitive with a diastema and canines sticking beyond other teeth.
Sexual dimorphism evident, males 45 kg and females 29 kg.
Has only been found in Ethiopia, Kenya and Tanzania. Well known examples
Well known examples
‘Lucy’ (3.2 mya) – a fossil that started major revisions in the understanding of
human evolution.
Lucy skeleton
Laetoli fossil footprints (3.7 mya) – trace fossils that show bipedal walking as the
big toe is in line with the other toes.
Laetoli footprints
2. Australopithecus africanus (2.0 – 3.0 mya)
Between 2 and 3 million years ago, a hominin with a mixture of ape and human
characteristics lived in the Gauteng highveld. This ape-man, Australopithecus
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africanus (the ‘southern ape of Africa’), was less ape-like than earlier
australopithecines. It may well have been the ancestor of our own genus Homo.
Diagnostic features – Australopithecus africanus
Quite short, about 1.1 – 1.4 m.
Brain capacity of 450 cc. See skull on p 278.
Slight build, probably with long arms and shorter legs.
Skull with less prominent brow ridges, higher forehead and shorter face than earlier
australopithecines.
Teeth and jaws much larger than humans, a u-shaped palate, reduced canine teeth
and no diastema.
Has only been found in South Africa.
Lived in small social groups and ate fruits and leaves and probably scavenged on
the remains of animals killed by predators. Why do you think they scavenged rather
than hunted? And, why would meat-eating be important in evolution of hominins?
Well-known examples
‘Taung Child’ (2.5 mya) – a remarkably well-preserved 3-year-old child’s skull and
an endocranial cast of its brain. Found in 1924, but it took over 20 years before
scientists accepted that Africa was the major place of human evolution.
‘Taung’ child’
Left skull: notice human-like teeth
Right skull: notice rounded dental arch, human-like teeth, absence of large canines,
lack of a large gap (diastema) between incisors and canines, and a brain that was
proportionally larger than that of an ape
‘Mrs Ples’ (2 mya)– the most complete skull ever found in South Africa of an Au.
africanus specimen.
Mrs Ples (adult)
On the left is a view of the base of the skull, clearly showing the position of the
foramen magnum or ‘large hole’. This is the point at which the spinal cord passes
through to the brain and the skull articulates with the vertebral column. Its position
indicates these creatures were fully bipedal.
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‘Little Foot’ (2.2–3.3 mya)– an amazingly complete fossil of an australopithecine.
What features of Australopithecus africanus show evolution towards Homo?
A larger brain than A. afarensis (450 cc)
Upright and fully bipedal, as evidenced by the position of foramen magnum
Human-like teeth (no large canines and no diastema between canines and incisors)
Rounded dental arch
Recent isotope studies of teeth have suggested they ate quite a lot of meat, which
they probably scavenged. Why do you think they scavenged rather than hunted?
And why would meat-eating be important in evolution of hominins?
Larger body, 45 kg – heavier than A. afarensis
According to archaeological evidence this species might have made primitive stone
tools such as stone choppers. The first stone tool used and made was at least 2.6
mya; such tools have been discovered at sites that are the same age as these
Australopithecus africanus fossils.
A. africanus also has some ape-like features; longer arms relative to legs, flattened
nose and forward projecting jaw. If the nose was flattened, what sense do you think
had become more important?
3. Australopithecus sediba (2.0 – 1.7 mya)
sediba = wellspring, a Sotho word
Australopithecus sediba is a proposed new species of Australopithecus, which lived

at about the same time as the oldest Homo ergaster fossils. It is an odd blend of
primitive and modern hominin traits that makes it a possible candidate for the
immediate ancestor of Homo sapiens.
Diagnostic features – Australopithecus sediba
Height 1.2 m.
Skull has brow ridges, no cranial ridge.
Less prognathous.
Australopithecine traits – small brain capacity, long arms, short strong hands suitable
for climbing.
Homo traits – wider and shallower pelvis, long legs capable of striding and possibly
running like a human and relatively small premolars and molars, short canines.
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Skull of Australopithecus sediba
Two partial skeletons of a new australopithecine species, Australopithecus sediba (2

mya) were found Malapa in the Cradle of Humankind and identified by Professor Lee
Berger of the University of the Witwatersrand in 2008. The skeletal remains of one,
an 11 to 12 year old boy, includes the most complete undistorted pelvis and ancient
hand ever yet found.
Berger with an almost complete skull and partial skeleton of Australopithecus

sediba
Assembled hand bones
Au. sediba may be a ‘key transitional species’ between Au. africanus and the
early Homo species. This is because it is more similar to Homo than to any other
australopithecine, which makes it a possible candidate for the ancestor of Homo. If
this is correct, these fossils could yield a great deal of information about the origins
and ancestor of the genus Homo.
4. Australopithecus (Paranthropus) robustus (2.0 – 1.2 mya)
These bipedal, small-brained australopithecines are not regarded as ancestral to

humans. They are now usually called Paranthropus.
Diagnostic features – Paranthropus robustus
Height 1.1 – 1.3 m.
Brain capacity of about 530 cc.
Face long, broad and flat with very small forehead, heavy brow ridges and sagittal
crest (for the attachment of chewing muscles). See next column.
Heavy build with relatively long arms.
Small incisors and canines, huge molars in a large, lower jaw. Indicates a vegetarian
diet. Possibly an adaptation to the drier African environment.
The most common hominin fossil in southern Africa.
Paranthropus robustus– front and side view
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Learning activity 8
Australopithecines
Question 1
1.The Tribe Hominini has four genera; Australopithecus is one, what are the other
three? (3)
2.The australopithecines are in some ways similar to the African apes. What is the
one significant anatomical and behavioural difference? (1)
[4]
Question 2
This skeleton is of an australopithecine. After studying it, answer the questions that
follow.
1.What could an anthropologist determine about its way of life by looking at this
skeleton? Give reasons for your answers. (6 x 2 = 12)
2.What species of Australopithecus does this skeleton represent? (1)
[13]
Question 3
1.Give the popular names of the two very famous A. africanus examples and by
whom and when they were discovered. (6)
2.By looking at the photographs of the skull of Mrs Ples what one feature shows this
hominin was bipedal? (1)
3.What is so significant about the finding of the skeleton of ‘Little Foot’, an

australopithecine? (1)
[8]
Total [25]
Learning activity 9
Australopithecines
Question 1
The following diagrams, A, B and C, represent pelvises and lower limb bones of an
australopithecine (Australopithecus afarensis), a chimpanzee and a modern human.
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1.Name the top leg bone. (1)
2.What do you notice, in each of A, B and C, about the relationship of this bone to
the midline (M)? (2)
3.In which are the foot and knee further from the midline? (1)
4.In which is/are the pelvis(es) adapted to support the weight of the body in an
upright position? (2)
5.What is the essential difference between the two types of pelvises? Use the letters,
A, B and C in your answer. (2)
6.Explain the trend in the position of the big toes of each. (3)
7.In diagram A explain, with a reason, what the big toe tells you about the habits of
this species? (2)
8.Which foot would enable an efficient upright bipedal stride? (1) Why? (1)
9.Which diagram represents Au. afarensis? Give reasons for your answer. (1 + 4)
10.Why do you think chimpanzees waddle when trying to walk upright? (3)
11.Underline the correct word from between brackets.

The femur of the human is (angled/not angled) and knee and foot are (further
from/nearer) the midline of the body. (2)
12.What do you notice about the femur of Au. afarensis? Did it waddle or stride? (2)
[27]
Question 2
This is a reconstructed australopithecine skull. After studying it, answer the

questions that follow.
1.Give three ape-like features of this skull. (3)
2.What can you assume about its brain capacity? Why? (1 + 1)
3.Giving one reason suggest what species of Australopithecus this skeleton

represents. (2)
[7]
Question 3
1.For what time period did australopithecines live? (1)
2.Give the popular names of the two very famous Au. africanus examples. (2)
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3.Why do the Laetoli fossil footprints show that the hominin was bipedal? (1)
4.Which australopithecines
4.1probably ate large quantities of coarse plant material? (1)
4.2had the smallest brain capacity? (1)
[6]
Total [40]
C. Homo
The genus Homo, to which we belong, began to appear about 2.4 mya. Some of
the Homo species co-existed with the australopithecines for about 1 million years.
These early Homos have been found at many fossil sites in Africa. It seems a
possibility that dramatic climate change between 2 and 3 million years ago created
evolutionary pressure on the ape-men (australopithecines) living in the Cradle of
Humankind.
Speciation occurred and a certain group of the australopithecines,

possibly Australopithecus africanus, may have started resembling the earliest
members of our own genus.
Unlike the Australopithecus species, fossils of some of the later Homo species are
found in places other than Africa, e.g. China, Java and Europe.
Diagnostic features – Homo genus
Height 1.3 m – 2 m, posture erect.
Foramen magnum centrally placed under skull.
Hands (long thumbs) smaller than its feet.
Brain large and more complex (700 cc in early homo to 1 350 cc in modern man).
This lead to noticeable new behaviours, e.g. sophisticated tool-making, more
advanced hunting methods, etc.
Dexterous hands enabled tool-making.
Skull with:
–less prominent brow ridges
–flatter face
–no skull ridge (sagittal crest)
–human teeth (small molars and no large canines)
–parabolic palate (dental arch).

500
Omnivorous, meat a large part of their diet.
Some examples of Homo
The hominins of the genus Homo include the following species.
Homo habilis
Homo ergaster (African Homo erectus)
Homo heidelbergensis (archaic Homo sapiens)
Homo neanderthalensis
Homo sapiens (anatomically modern Homo sapiens)
1. Homo habilis (2.4 to 1.6 mya)
Homo habilis is regarded as the first species of the genus to which we belong.
Appearing about 2.4 mya, H. habilis, also known as ‘handy man,’ was a turning point
in human evolution because its brain is about 20% larger than its ancestors. This is a
huge increase, and because of this H. habilis developed a characteristic that is
uniquely human, the making of tools. H. habilis survived for about 800 000 years,
becoming a taller, stronger, smarter species of hominin.
Diagnostic features – Homo habilis
Robust skeleton with relatively long arms and shorter legs.
Brain capacity about 700 cc.
Cranium rounded, large brow ridges, no forehead and a slightly projecting face.
Molars large and narrow with strong jaw.
First hominin tool-maker used tools to scavenge kills. Tools possibly necessary for
survival as climate change probably reduced choice of plant foods.
Lived in East Africa.
Skull reconstruction and artist’s impression of Homo habilis
An incident two million years ago
Question 1
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Read the following text that describes how scientists imagined an incident in the life
of Homo habilis two million years ago. Then answer the questions that folow.
The robust (Australopithecus robustus) duo are so intent on consuming a delicacy of

white termite larvae that they are oblivious to the lions and to a group of four or five
other bipedal creatures that have emerged from the riverine bush and are walking
steadily towards the lions. These hominins are different from the robusts. Although
they are not much larger they walk with more confidence. Their heads are bigger, yet
more refined, without the more pronounced jaws of the robusts.
These habilines, among the first of our own genus, Homo, are more man-ape than
ape-man. Their focus is not the big cats, but their kill, the bloody zebra carcass that
still has some meat on the bones. The lions, aware of their approach, rise from their
positions and circle their kill. The male lion roars a warning, but the hominins do not
waver until they are 20 metres away. Then they suddenly start making a big noise,
leaping up and down, shouting and brandishing a big stick. This behaviour clearly
confuses the lions, which are used to most other animals running away from them.
One of the habilines reaches down and picks up a river cobble from the ground.
Holding it in his right hand, he somewhat clumsily casts the rock at the largest male
lion, which flinches back from the near miss. Almost immediately all the other man-
apes join in the activity and a torrent of stones rains down on the lions, several
stones finding their mark. The lions, who had eaten their fill, retreat quickly,
disappearing into the thick galley forest, glancing angrily back at the now triumphant
man-apes who have claimed the kill and are jumping, hooting and slapping each
other in what might be interpreted as a victory dance.
The man-apes approach the carcass. One of them picks up two stones that were
hurled at the lions, and begins striking them against each other to create a sharp
edge on an impromptu stone blade.
The clicking of rocks ends quickly and the members of the small troop gather around
the toolmaker, pick up small flakes and the large cobble remains and they walk over
to the carcass. With amazing speed and efficiency they slice the skin with sharp
flakes and bash open bones with the larger cobbles to extract the juicy marrow. They
exchange sounds in what may, at a stretch of the imagination, be called language
rather than animal communication. Some of the individuals pick up pieces of bone
and meat and walk off into the woods, maybe carrying food back to the troop.
Excerpt from Cradle of Humankind (Brett Hilton-Barber & Prof. Lee R. Berger), p
9125
1.In line 12 what does the term ‘habilines’ refer to? (1)
2.What in the text suggests that, due to an ice age, the tropical forests had retreated
to the extent that trees were only found on the edge of the rivers? (2)
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3.What one term describes the landscape of open grassland with fewer trees? (1)
4.What do you think the text in lines 7 to 9 means by ‘These hominins... walk with
more confidence’? (2)
5.Pretend you are an anthropologist; by using information in the text give five
reasons why you think the habilines had a more highly developed brain than the
australopithecines. (8)
6.Archaeological evidence has shown that these habilines were tool-makers. Using
information from the text explain in your own words how they made these simple
tools and how they used them. (3)
7.Would this type of food gathering be called scavenging or hunting? Validate your
answer. (3)
8.What positive effects could the eating of meat have on this species? (2)
9.Write down at least three characteristics of this species that an anthropologist

would use to show signs of this hominin evolving towards a modern human. (3)
[25]
Question 2
Using the information you gleaned from the whole of this section on Homo habilis,
including the learning activity, list five features that show evolutionary progress
towards H. sapiens.
[5]
Total [30]
2. Homo ergaster (2.0 – 1.4 mya)
About 2 mya a new species arose, Homo ergaster. This species is more near-human
than man-ape and is now widely accepted to be the direct ancestor of modern
humans. They lived in East and Southern Africa.
Diagnostic features – Homo ergaster
Height about 1.85 m, same as modern humans.
Skeleton robust, the earliest hominin to have human-like body proportions, i.e. the
legs are longer and arms relatively shorter. This allowed long distances walking and
maybe even running.
Brain capacity is 850 cc, about three quarters the size of human brain. Sophisticated
tool-making and more advanced hunting methods therefore possible.
Face more vertical, chinless, brow ridges, smaller teeth.
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Efficient hunter of small mammals.
First species to use and control fire, about 1.5 mya.
Skull reconstruction and artist’s impression of Homo ergaster
Well-known example
‘Turkana boy’ – 90% complete skeleton, the best preserved early Homo fossil yet
found.
3. ‘Homo erectus (1.8 to 0.3 mya)
It is thought that Homo ergaster was the first to venture out of Africa and go to Asia.
Here it possibly gave rise to a very similar hominin known as Homo erectus, found in
Java, Indonesia. This species had a larger brain capacity (1 000 cc) than H.
ergaster.
What features of Homo erectus show that it had progressed towards Homo sapiens?
The following features of Homo erectus show evolutionary progress.
The males were as tall as modern humans, 150 to 180 cm.
They were both powerful and graceful, and perfectly adapted to bipedal locomotion.
Their adult brain capacity was about 1 000 cc; about three quarters of a modern
human’s brain.
They were tool-makers and tool-users.

At H. erectus sites archaeologists found slightly more advanced tools known as
Acheulian (1.5 mya to 200 000 years ago). Their complexity showed for the first time
in the fossil record a central core of a stone, with bits chipped off.
The main tools were hand-axes and cleavers. The hand-axe, a bifacial teardrop-
shaped tool, was probably used for a very wide variety of tasks.
Bifacial hand-axe
With their tool kit Homo erectus became an efficient hunter of small mammals, and
was able to live on a mixed diet of meat and plants.
Homo erectus was the first species to use and control fire, about a million and a
half years ago.
At the Cradle of Humankind, anthropologists found 279 fragments of burnt bones
that on analysis showed they had been burnt at high temperatures in the hearth of a
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campfire, not just in a natural fire. This is so far the oldest evidence in Southern
Africa for the controlled use of fire, though in East Africa there is slightly older
evidence.
Fire was probably initially gathered from fires caused by lightning strikes.
Swartkrans Cave – oldest evidence of controlled use of fire
What can the use of fires tell us about the lifestyle of H. erectus?
The control and use of fire is highly significant as it enables anthropologists to

determine a fair amount about the lifestyle of these early hominins – H. erectus / H.
ergaster (African H. erectus).
Fire could have:
led to social behaviour with the warmth and extended ‘daylight’ hours.
encouraged conversation and teaching.
offered more permanent (but still temporary) dwelling sites.
given a measure of protection from predators at night.
helped in co-operative hunting by herding animals away from fire.
provided humans with roast meat making it more appetizing. This could have
resulted in more protein being eaten, which may have aided brain development.
a wider choice of food, including smoked and dried fish and meat, and led to the
invention of cooking.
been a sign of intelligence, as keeping a fire going showed forward planning.
enabled better, stronger tools to be made that would have led to more successful
hunting.
been a factor that enabled H. erectus to migrate out of Africa and into colder climates
in Europe and Asia.
The controlled use of fire marked a crucial change in human behaviour as it showed
they had the ability to adjust the environment to suit their needs.
Advantages of fire
Design one simple diagram, no words, to show eight aspects of the ‘new’ lifestyle
that fires offered.
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We take so much for granted, don’t we?
4. Homo heidelbergensis (700 000 to 200 000 ya)
Homo heidelbergensis shows traits similar to both Homo ergaster and modern Homo
sapiens suggesting that ergaster might have given rise to H. heildelbergensis. It is
often referred to as archaic Homo sapiens, and existed until the appearance of
anatomically modern H. sapiens 200 000 ya.
Diagnostic features – Homo heidelbergensis
Skeleton robust, as tall as or taller than modern humans.
Brain capacity about 1200cc.
Cranium rounded, large brow ridges, flatter face than earlier Homo species.
First species to hunt in groups, often with wooden spears, and build simple wood
and rock dwellings.
Possible ancestor of modern humans. The human remains, mostly from the Cape
coast of South Africa, are thought to be of this species.
An artist’s impression of Homo heidelbergensis and its skull
5. Homo neanderthalensis (235 000 to 30 000 ya)
Some extinct species of the genus Homo found in Europe probably gave rise to the
Neanderthals (Homo neanderthalensis) in Europe and western Asia. They existed
during an ice age. Even though H. sapiens and H. neanderthalensis were
contemporaries for approximately 10 000 years recent mtDNA studies indicate that
there was no interbreeding between these two species.
Neanderthals are not the direct ancestors of modern humans; they were a dead end.
However, they are our closest extinct relatives.
Diagnostic features – Homo neanderthalensis
Height about 1.6 m, heavy skeleton.

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Large brain (1450 cc) but forebrain smaller than modern humans.
Skull with low cranium, smaller brow ridges, forehead that slopes back, long face.
Little evidence of technological development as hunting was done with simple tool
kits.
Shares some cultural traits with modern humans, e.g. burial of the dead.
Disappeared, possibly out-competed by Homo heidelbergensis who had more

advanced skills.
6. Anatomically modern Homo sapiens – (from 200 000 ya to present)
About 200 000 ya a new type of Homo, anatomically equivalent to modern humans,
began to emerge in Africa. It is known as modern Homo sapiens – ‘the symbol user’.
There is archaeological evidence of cultural activities, e.g. art and human burials,
from about 100 000 years ago. It is assumed that the increase in brain size was
responsible for those activities.
Diagnostic features– modern Homo sapiens
Height (1.6 -1.8 m), taller than earlier Homo species.
Build slender, upright.
Brain capacity about 1350 cc.
Foramen magnum placed centrally under skull.
Skull well-rounded, forehead flat and near vertical, face small and flattened, small or
no brow ridges, small jaw with smallest teeth of the Homo species.
Legs are longer and arms shorter.
Chin is strong, possibly created a larger space below the tongue for the development
of language.
Feet have parallel toes – big toe enlarged and others are small, heel bone large and
longitudinal arch rigid. Arch absorbs shock and gives propulsive spring while
walking.
A skilled hunter, tool-maker and artist.
Emerged in Africa.
Skull of Homo sapiens
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What anatomical features do anatomically modern H. sapiens have that show
evolutionary progress?
Anatomical features that show evolutionary progress from archaic Homo

sapiens are:
a more slender build
a dome-shaped skull with a large sharply rising forehead. The increased frontal lobe
area contains amongst other features the centre for speech.
eyebrow ridges that are very small or more usually absent
a large brain (1360 cc)
a small flattened face. Their nose is small, implying less dependence on smell.
smaller teeth in an arched lower jaw
eye teeth the same height as other teeth
a prominent chin. It has been suggested that the chin created a larger space below
the tongue, allowing the development of language.
Not all the features can be seen in the picture below.
Anthropologists consider that the use of more complex tools, language and co-
operative behaviour are all mutually-dependent. All these qualities together would
have promoted and necessitated the larger brain found in anatomically
modern Homo sapiens.
Hominin skull identification
Question 1
Act as a palaeontologist and give the name of the species for each of the hominin
skulls illustrated below. With reference to the following list, give a description of up to
four key features that help in its identification. You will have to go through your
notes carefully looking at pictures and drawings and reading the text – enjoy!
Shape of skull
Size of braincase compared to rest of skull
Sloped or flat facial angle
Presence or absence of snout
Presence or absence of brow ridges

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Robustness of jaw
Size of teeth
Development of chin
Species include: modern Homo sapiens, Homo ergaster, Homo heidelbergensis,

Paranthropus robustus, Australopithecus africanus, Australopithecus afarensis
Skull number 1 1.Species________________
Features________________
________________
Features________________
________________
Features________________
________________
Features________________
________________
Features________________
________________
Features________________
________________
[25]
Question 2
1.Fill in the approximate greatest age and brain capacities for the following
species. Various sources give slightly different brain capacities.
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Hominin Greatest known age Brain capacity/cc
Australopithecus afarensis
Au. africanus
Homo habilis
H. ergaster
modern H. sapiens
(10)
2.Draw a bar graph to represent the average brain capacities in the above hominins.
The graph must be labelled to make it fully understandable.
(9)
3.Mention six general observation(s) or conclusion(s) that can be drawn from the
graph.
(6)
[25]
Total [50]
Evolution of hominin features in Africa
Complete the table below to show how physical features evolved in hominins over
time. In order to find all the information, you will need to think and refer to different
places in this unit.
Au. africanus H. habilis H. ergaster H. sapiens
Age – mya
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Skull
brain capacity
brow and cranial ridge
shape of face (prognathism)
foramen magnum position
teeth
Skeleton
robustness
overall size
posture
length of limbs
hand features
foot features
Negative marking
Total [30]
Worldwide distribution of hominin fossils
Africa is the only continent where Homo fossils earlier than 2 mya have been found.
Later homo fossils from about 2 mya to recent times have been found in Africa, Asia
and Europe.
Diagram showing where and when the main Australopithecine

and Homo fossils have been found
What does the above information suggest about the point of origin of the Homo
species?
African hominin fossil sites
The many fossil sites in Africa have made an enormous contribution to the
understanding of human evolution.
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However, it is from two main areas that almost all the early hominin (Ardipithecus,
Australopithecus and Homo) fossils have been found. These areas are East Africa,
in the Great Rift Valley, and South Africa, particularly the Cradle of Humankind.
Great Rift Valley
The 2 000-kilometres-long Great Rift Valley is a very distinctive and dramatic

geological feature in East Africa (Kenya and Tanzania) and Ethiopia. The rift opened
up approximately 65 million years ago, shortly after the dinosaurs became extinct.
The very steep sides of the rift valley produced a lot of sediment. This sediment
landed in the rivers and lakes where hominins or their remains became trapped and
eventually fossilised. The sediment formed a number of layers of sedimentary rock
or beds many of which contain fossil hominins.
Rift Valley (Olduvai Gorge) showing sedimentary layers
There are many important sites. See the map below. These sites have produced a
greater variety of fossil hominins than anywhere else in the world. While the fossils
are largely found in the sedimentary rocks, hominin traces, e.g. footprints, have been
preserved in ash from active volcanoes.
Map to show position of Great Rift Valley fossil sites
Great Rift Valley fossil sites, their fossils and paleontologist(s)
Fossils Name of fossil (genus and Fossil site Palaeontologist/s who

age (mya) species) and common and country found fossil
name
4.4 Ardipithecus ramidus / ‘Ardi’ Aramis in Tim White

Ethiopia
3.7 Australopithecus afarensis Laetoli in Tim White

Tanzania
3.2 Australopithecus afarensis / Hadar in Donald Johansen

‘Lucy’ Ethiopia
2.4 Homo habilis Olduvai Louis and Philip Tobias
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Gorge in
Tanzania
2 Homo ergaster Olduvai Louis and Mary Leakey

Gorge in
Tanzania
1.7 Homo ergaster / ‘Turkana Turkana in Richard Leakey

boy’ Kenya
0.195 Homo sapiens’ / Omo Omo site in Richard Leakey

remains Ethiopia
Cradle of Humankind
Sterkfontein, Swartkrans and Kromdraai are part of a set of about 500 limestone
caves of special interest to palaeo-anthropologists as they are among the most
prolific fossil sites in the world.
Sterkfontein was declared a World Heritage Site in 2 000 and the area in which it is
situated was named the Cradle of Humankind. It lies in Gauteng province near the
town of Krugersdorp.
Map of South Africa to show the Cradle of Humankind and other Homo fossil
sites
The Sterkfontein fossils are found in limestone caves embedded in a mixture of

limestone and other sediments called breccia that fossilised over time. This is unlike
the East African fossil sites, which are laid down in beds.
breccia = a rock type formed from mineralised sediment that has fallen into caves
It is from the breccia that fossil bones, plant remains and stone tools (artefacts),
which tell us about life around the caves from 3.5 to 1.5 mya, have been (and are still
being) excavated. About 500 hominin fossils have been found at Sterkfontein. This
represents about 40 percent of all hominin fossils found so far making it the richest
site in the world for finding ancestors of modern humans.
It seems that early hominins did not live in the caves; their remains probably were
dropped by leopards from kills stored in trees or washed into the cave with rains, the
bones becoming preserved within the breccia. Most of the fossils are disarticulated
because the hominins were either partly eaten or because porcupines dragged the
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hominin remains into the caves. The animals chewed the bones to sharpen their
continuously growing teeth.
Limestone cave
Some important fossil and archaeological finds in the Cradle of Humankind
The first adult Australopithecus – Mrs Ples (2 to 3 mya).
The only almost complete Australopithecus skeleton – Little Foot.
The oldest stone tools from the Oldowan culture indicating that Homo habilis might
have lived in the area.
The largest number of Australopithecus africanus fossils.
A new fossils species announced in 2010, Australopithecus sediba that has a mix of
primitive features typical of australopithecines and more advanced characteristics
typical of later hominins.
Note:
Maropeng, the visitors’ centre of the Cradle of Humankind tells the story of the
origin of humankind, and their continuing journey into the future. Maropeng means
‘returning to the place of our origins’.
A visit to Maropeng is a must for all – it tells us so much about our human
origins.
Why are the Cradle of Humankind fossils so important?
While the Cradle of Humankind fossils have already told us many, many things about
our pre-history, new findings will teach us even more. So far, from these fossils, we
have learnt the following important aspects about human evolution.
An early ancestor of H. sapiens existed in South Africa

Between 2 and 3 mya years ago a 1.3 m tall hominin with a blend of ape and human
characteristics lived on the Gauteng Highveld. The ape-man (Australopithecus
africanus) may well have been the ancestor of our own genus, Homo.
Australopithecus africanus seems to be endemic to South Africa as no remains of
this species have been found anywhere else in the world supports the Out of Africa
hypothesis.
A hominin speciation event took place in South Africa

The climate changed between 2 and 3 mya which put evolutionary pressure on the
ape-man. As a result between 2 and 2.5 mya years ago speciation occurred and the
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ape-men started taking on different characteristics that eventually would lead to two
separate species. One with a flatter face and larger teeth, a robust ape-
man, Parathropus robustus and another, Homo habilis that started to look like the
earliest members of our own species.
Two closely related hominin species co-existed in South Africa
Around 2 mya Australopithecus africanus disappeared from the fossil record and the
two ‘new’ species co-existed for hundreds of thousands of years, using basic tools
and living in different ecological niches. P. robustus possibly used bone tools and
was vegetarian while H. habilis used stone tools and had a varied diet that included
meat and plants. Meat may have given H. habilis an advantage as its brain could
have developed further helping it evolve into the Homo line that exists today.
A hominin genus became extinct
The robust Paranthropus species, while living for about 1 million years became
extinct 1 mya. It is not known what caused this. It could well have been direct
competition with Homo, which was becoming skilled in extensive bone and stone
technology, or it could have been a variety of other issues, including a slower
reproductive rate.
The hominin brain evolved
By about 1.5 mya a new species started emerging, African H. erectus(H. ergaster).
The evidence of this is the more sophisticated stone tools, e.g. million-year-old hand
axes at the Gladysvale and Plover’s Lake sites. The improved stone tools showed
evolution of the brain. In turn it enabled these hominins to catch fast moving prey
and thus live in the harsh, drier African environment.
Homo neanderthalis disappeared about 30 000 years ago
African fossil sites
By referring to relevant parts of this unit answer the questions that follow.
Question 1
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1.On the map, fill in the names of the two major fossil sites (A and B) and the
countries where they are found (C, D, E, and F) (6)
2.Give the name and age of the oldest hominin fossil. Name the country in which it
was found. (3)
3.How old was Australopithecus afarensis (also known as Lucy)? Write down the
letter of the country in which it was found. (2)
4.Provide the popular names of the two famous Australopithecus africanus fossils
found by Robert Broom and Raymond Dart. How old are these? Write down the
letter of the country in which they were found. (4)
5.Name the first Homo species. Write down the letter of the country in which it has
been found. (3)
6.Write down the letters of the countries in which fossil remains of H. sapiens have
been found. (4) No marks for obvious guessing.
7.Having answered the previous questions comment on:
7.1the distribution of the oldest hominin species. (1)
7.2the obvious differences between the fossils found in F and D. (2)
8.Who were the palaeontologists who first discovered and named a Homo
habilis fossil? (2)
9.Who was the American palaeontologist who was involved with the discovery of one
of the earliest hominins, Ardipithecus ramidus as well as the footprints
of Australopithecus afarensis? (1)
10.Describe simply the difference in fossilisation of hominin remains in the Great Rift
Valley and in the Cradle of Humankind. (6)
11.Which cave in the Cradle of Humankind is probably the richest hominin site in the
world? (1)
12.At which site and by who was the most complete Homo ergaster (African Homo
erectus) fossil discovered? What was the common name of this fossil? (3)
13.In 2008 Professor Lee Berger discovered what seems to be a new hominin
species. Name the fossil site where this species was found and give its scientific
name. (3)
14.In which country were the Omo fossils found. What hominin species are these
and how old are they estimated to be? (3)
15.Give the letter of the country where Australopithecus africanus is exclusively

found. (1)
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Total [45]
Have you learnt quite a lot from doing this activity?
How can bipedalism, fire making, tool-making, language and culture be seen as
interdependent?
About 20 million years ago the climate became drier and the forests in Africa started
shrinking. This environmental change brought new selection pressures. Any ape-like
beings that could walk upright and move easily across the open areas with fewer
trees were selected for survival as they could adapt better to the new environment.
Bipedalism is considered the major feature that enabled ape-like men to evolve into
modern man. From this arose the development of the other qualities such as fire-
making, tool-making, language and culture.
The upright stance freed the hands, which made possible a variety of new activities
such as carrying and tool-making. The initial tools, in stone, were made by Homo
habilis. With these tools they could successfully collect (scavenge) meat from
animals killed by other animals. The extra protein acquired this way helped with the
development of the brain, which over time led to the making of more diverse and
sophisticated stone tools by the hominins. This enabled them to change from
scavenging to hunting.
At the same time these hominins discovered the use of fire. This led to great
changes in their way of life. Fire hearths lead to the development of integrated
groups living in camps which stimulated co-operative behaviour, e.g. organized
hunting, which needed technical skill, planning, division of labour and a simple
system of communication which later developed into speech. Social living and a
more complex brain, the capacity of which increased over time from about 775 cc to
1225 cc, lead to more complex behaviour which led to the development of the
human cultures such as clothing, the building of shelters, rock engravings and
paintings and religious rituals surrounding the burial of the dead.
Fires also led to another important change. Diet switched from raw to cooked food
with more extensive meat-eating. It is commonly agreed that cooked food yields
more nutrients resulting in further development of the cerebrum.
These characteristics are all interdependent and increased the hominin’s ability to
adapt to and to modify their environments.
Interdependence of bipedalism, fire making, tool-making, language and culture
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Design a clear mind map to show how bipedalism, fire making, tool-making,
language and culture be seen as interdependent.
Spread of modern humans around the world
There are two main hypotheses. They both agree that Homo erectus evolved in
Africa and spread to the rest of the world around 1 to 2 million years ago; it is
regarding the more recent history where there is disagreement.
Multiregional view
The multiregional hypothesis suggests that Homo sapiens evolved independently in

different regions from distinctive populations of archaic forms (such as Neanderthal
and Homo erectus). Only a few scientists support this hypothesis today.
Scientists believe modern humans first appeared in North Africa between 200 000
and 150 000 years ago.
The ‘Out of Africa’ (OOA) hypothesis proposes that modern humans evolved in
Africa from early humans, i.e. archaic Homo sapiens (H. heidelbergensis), and then
dispersed to other regions, where they replaced existing hominin species. This small
population of modern humans then spread into Europe and Asia about 60 000 years
ago and afterwards around the world. Over time these humans displaced and
eventually replaced, without genetic mixing all other early human populations
(Neanderthals and Homo erectus), probably because of their superior technology
and communication skills.
The hypothesis of a single origin of modern humans in Africa is today the one
accepted by most scientists.
The evidence for this hypothesis comes from a combination of sources.
1.Fossils
2.Genetic links, mtDNA
3.Archaeology
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1. Fossils
It is in Africa that the oldest modern Homo sapiens fossils have been found, e.g. the
Omo H. sapiens fossil remains, which date to 195 000 years ago. Fossils of all other
modern H. sapiens found outside of Africa date to more recent times. This suggests
strongly that modern H. sapiens originated in Africa. This is supported by genetic
evidence.
2. Genetic links
Until recently the only way of learning about early Homo sapiens was through fossil
remains and stone tools. Now geneticists use DNA, nuclear and mitochondrial, to
propose where H. sapiens probably evolved and work out when this might have
happened. Geneticists preferably use mitochondrial DNA (mtDNA) to study human
origins and migrations. This is because it:
is a shorter molecule than nuclear DNA.
mutates more quickly than nuclear DNA.
passes unchanged from mother to offspring.
These properties make it easier to detect any changes or variations that occur in
the mtDNA molecule. It is the variations that are important for these studies. Each
variation (a mutation) is called a marker. As mtDNA mutates at a known rate the age
of a lineage can be worked out. Therefore races with the greatest number of markers
are the oldest populations, and the least, the youngest population.
How does genetics show where modern Homo sapiens originated?
Geneticists compared markers from mtDNA that had accumulated in humans from
around the world. They found that the indigenous African people have the greatest
number of different markers, nearly double that of any other group anywhere in the
world. The large number of variations could only have evolved over a long period of
time. Therefore the African populations must be the oldest. Thus, H. sapiens must
have originated in Africa. This can be seen in the cladogram in the next column.
How does genetics show when modern Homo sapiens originated?
The differences in markers between two population groups tell scientists how long
ago they separated.
As mentioned earlier if there are few differences (markers), they separated recently.
Many differences indicate that they separated a long time ago.
By comparing mtDNA genetic markers geneticists have concluded that the last
female common ancestor, with a genetic marker found in all living humans, must
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have lived roughly 150 000 years ago in Africa (Ethiopia or Sudan) –
a ‘Mitochondrial Eve’.
While 150 000 years ago is not exactly the same as the dating of the earliest
modern H. sapiens fossil (195 000) it is remarkably similar. So evidence from both
genetics and fossils tell us the same thing, modern Homo sapiens had its origin in
Africa between 195 000 and 200 000 years ago.
The cladogram below of the mtDNA relationships among various humans shows
that:
The original common ancestor of Homo sapiens lived about 200 000 years ago.
Bushmen (San) and indigenous African people have the greatest number of mtDNA
markers and are therefore the oldest populations on earth.
All non-indigenous African populations are descended from an African ancestor.
It is astonishingly to realise that all 7 billion people alive today have inherited the
same mitochondria, with its mtDNA, from this one woman, our most recent common
female ancestor.
Cladogram to show mt DNA relationships among humans
There probably were other lineages but they either died out or the mothers only
produced sons who could not pass on mtDNA.
When and to where did modern human migrate?
It is also possible using mtDNA to trace migratory dates and patterns. See the map
on the next page. All markers seen in non-Africans show the date of the earliest
successful ‘Out of Africa’ migration as being about 60 000 years ago. According to
the genetic markers the route was into the Middle East and then across the world
to Eurasia (50 000 years ago), Australia (40 000 years ago), Europe (40 000 years
ago) and the Americas (20 000 years ago). These dates can be very variable,
depending on the source used. However, the route and relative dates are correct.
The further one goes from Africa where there are fewer differences in genetic
markers between groups. This means these are ‘newer’ populations.
‘Out of Africa’ model
How are human populations linked genetically?
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By examining mtDNA sequences in different populations, geneticists can determine
the closeness of relationships between populations (or within populations). Certain
similarities in the genetic makeup of humans let genetic anthropologists determine
whether or not different groups of people came from the same geographical area.
This is significant because it allows anthropologists to trace patterns of migration and
settlement, which gives helpful insight as to how contemporary populations have
formed and progressed over time.
Note:
Each of us living today has mtDNA that contains the story of our ancient ancestors'
journeys.
Mitochondrial DNA extracted from bones of 38 000 year-old Neanderthal individual is

quite different from that of modern humans, strongly suggesting that modern humans
replaced Neanderthals in Europe without interbreeding.
The ‘Out of Africa’ hypothesis states that all modern humans originated in
Africa, and then migrated out of Africa to the rest of the world.
521
Figure 27: Migration out of Africa into the rest of the world.
522
Approximately 150 – 200 000 years ago, ancestors of Homo sapiens (such as
Homo erectus) evolved into Homo sapiens in eastern and southern Africa.
About 70 000 years ago, these modern humans spread out, into Europe, Asia
and across the world as illustrated in the map above (Figure 27).
Out of Africa hypothesis is supported by:
genetic evidence
the fossil record
Genetic evidence (mitochondrial DNA studies)
Using our current understanding of DNA, its structures and properties, scientists
have analysed human DNA to explore the relationships between humans across
the world.
Figure 28: Mitochondrial DNA found

inside mitochondria within a cell
523
Geneticists use mitochondrial DNA (mtDNA – Figure 28) to study human origins and
migrations since mtDNA is passed unchanged from mother to offspring. However,
during a person’s life, mutations (changes) to the mtDNA do occur.
Scientists can determine the rate at which such mutations (or markers) take
place, and can then use them as a type of molecular clock to determine the age of
a particular maternal mtDNA lineage. From the studies, we can conclude:
African populations of Homo sapiens have the greatest number of mtDNA

markers and are thus the oldest.
The most recent common ancestor whose genetic marker is found in all living
humans, must have lived in eastern Africa approximately 150 000 years ago.
Based on markers in non-African populations, scientists believe that modern

humans moved out of Africa about 60 – 70 000 years ago. It would have been an
ideal time.
524
‘Out of Africa’ Hypothesis
1.What is mitochondrial DNA (mtDNA)? (1)
2.How is mitochondrial DNA passed through generations? (1)
3.Who is the Mitochondrial Eve? (1)
4.Where and when did she live? (2)
5.What is the scientific basis that a ‘real’ Eve existed? (1)
6.How many years ago did the first Homo begin to appear? (1)
7.When did modern Homo sapiens migrate out of Africa? (1)
8.What was their migration route from Africa? (2)
9.When did modern humans first migrate into what is now Europe? (1)
10.In the ‘Out of Africa’ hypothesis, modern humans moved out of Africa to populate the
world. Describe the fate of the other human populations already inhabiting the regions
they moved into. Identify one example of such a population. (4)
11.What caused humans to evolve into different races with unique characteristics? (1)
12.Explain how mitochondrial DNA can be used to give evidence that modern humans
originated in Africa? (4)
Total [20]
Where do the San fit in?
The San (!Kung or bushmen) people of Southern Africa, who have lived as hunter-
gatherers for thousands of years, are likely to be the oldest extant population of
humans on earth.
!Kung = member of the San people who live in eastern Namibia and western Botswana
525
extant = living
Scientists have found that the San people have the oldest mtDNA lineage, shown by
their having the most genetic markers on their mtDNA. They are therefore the oldest
continuous population of humans on the continent – and on earth.
According to their genes they branched off from the original modern H. sapiens line very
early in human history, about 160 000 years ago.
Therefore they are directly descended from the original population of early human
ancestors who gave rise to all other groups of Africans and, eventually, to the people
who left the continent to populate other parts of the world.
It can be said that the San are remnants of human’s ancient ancestors and have a
unique place in the history of the world. Sadly, this uniqueness has been largely
overlooked. It is to the great discredit of other groups who moved into the San’s
homeland region, i.e. Southern Africa that the San have lost so much; they have been
killed, mistreated, moved out of their territory and discriminated against.
3. Archaeological evidence
One possible hypothesis about how modern Homo sapiens originated is that a
population of H. heildelbergensis (archaic H. sapiens) became isolated along the
southern coast of South Africa approximately 200 000 years ago. This group was cut off
from the interior by high mountains and the Karoo and Kalahari deserts. In this area
there were fewer of the animals they normally hunted. They therefore had to rely largely
on a seafood diet. Evidence of this is extensive shell middens at numerous places along
the southern coast. It is known that seafood contains high protein levels and omega-3
oils, which are essential for brain growth and development. This could have contributed
to the development of a more advanced human brain like that found in modern H.
sapiens.
The enlarged brain could be the reason H. sapiens developed to become a fully sensate
being that could think and communicate symbolically, was adaptable, self-aware and
creative and formed complex social and cultural groups.
What evidence is there in South Africa of early modern H. sapiens?
526
In recent years there have been amazing discoveries of human remains and their
artefacts in South Africa. They are the world’s oldest remains of our own species,
modern H. sapiens. If the dates below are correct then there were modern humans in
South Africa about 60 000 years before they went to Europe and Asia.
At Langebaan in the Western Cape, a set of human footprints, ‘Eve’s Footprints’,

dated as being made 117 000 years ago, was found recently.
Eve’s Footprints
At the Klasies River Caves near the Tsitsikamma River mouth, human remains with
anatomically modern human features were found dating back 115 000 years. These
remains were buried showing a modern human trait.
H. sapiens remains
In Border Cave in KwaZulu-Natal, the remains of an infant were found dating back to
about 100 000 years. It was buried in a grave with shell ornaments and has a red stain
possibly signifying that the body had been painted. This type of burial, like that in
Klasies River Caves, suggests early H. sapiens were capable of abstract and symbolic
thought and probably communicated in a fairly complex language.
Since the 1990s a team of archaeologists, lead by Christopher Henshilwood, have been
working at Blombos Cave on the southern coast of South Africa.
The finds at Blombos are revealing a great deal about the lives of H. sapiens about
75 000 ya. The site is famous for the discovery of the following artefacts.
–Pieces of engraved ochre that are 75 000 years old. The crisscross patterns are
almost certainly symbolic; members of the community must have understood the
meaning behind the designs.
527
Engraved ochre
–Beads made from shells that were deliberately pierced and probably strung together in
a necklace.
–Sophisticated bone tools 80 000 years old.
–An ochre tool kit 100 000 years old; with the first evidence of planning, making and
storage in a container (abalone shell) of substance, i.e. ochre powder. This is a good
example of evolution of cognitive functioning in early H. sapiens.
–Evidence for possibly the earliest shell fishing and fishing dating to 140 000 years ago.
While the preceding artefacts are evidence of modern humans living in the cave no
human remains apart from a few human teeth have been found.
Shell beads and tools
Pinnacle Point Cave (Mossel Bay)
Another cave of archaeological importance and interest is Pinnacle Point Cave near
Mossel Bay. It was occupied by humans between 170 000 and 40 000 years ago. This
site has the oldest evidence for:
collecting shellfish for food.
the heat treatment of rock to make stone tools.
using fire to make ochre artefacts.
Conclusion
All the finds from the coastal sites are evidence of modern human traits such as
symbolic thought and culture. They also provide the earliest evidence of modern human
behaviourshown for example by:
production of art (e.g. Blombos Cave)
burial of the dead (e.g. Klasies River Caves)
a complex hunting tool kit – pointed stone flake tools, long flake blade, finely worked
stone scrapers, blades for fishing (e.g. Blombos Cave)
528
The most interesting fact is that this happened in Southern Africa many, many
thousands of years earlier than similar sites in Europe. This could suggest that modern
forms of Homo sapiens evolved in Africa, maybe even in South Africa.
What an amazing history we have! Instead of complaining about a myriad of things

we should be proud and honoured to be South Africans.
Short questions
1. Multiple choice
1 2 3 4 5 6 7
8 9 10 11 12 13 14
[14]
1.African races are the oldest in the world because they have: (a) the greatest mtDNA
diversity of all human races. (b) more mtDNA than other races. (c) less than 95 percent
of the same DNA as other races. (d) have never moved from the continent.
2.Which is the incorrect answer for the following statement?

Although researchers agree on the general trends of hominin evolution, no complete
answers can be given. This is because: (a) the number of fossil examples from some
genera is very small. (b) the fossils that they have are often very incomplete. (c) there
are large time gaps in the fossil records. (d) living forms look exactly like fossil forms.
3.Homo species have: (a) hands with short thumbs. (b) centrally placed foramen
magnum. (c) a sloping face. (d) brains with a capacity of 500 cc.
4.The most complete Australopithecine fossil yet found has the nickname of: (a) Mrs
Ples; (b) Turkana Boy; (c) Taung Child; (d) Little Foot.
529
5.The diagnostic features of a modern human skull are: (a) flat face, brow ridges, dome-
shaped skull. (b) chin, dome-shape skull, flat face. (c) sloped face, chin, dome-shaped
skull. (d) sloped face, large canines, flat cranium.
6.Human evolution shows the transition from a: (a) long-armed, short-legged to short-
armed, long-legged hominin. (b) long-armed, long-legged to short-armed, short-legged
hominin. (c) short armed, long-legged to long-armed, short legged hominin. (d) none of
these options.
7.The earliest australopithecines evolved from apes about _________ million years ago.
(a) 1-2; (b) 2-3; (c) 3-5; (d) 5-7
8.Which hominid had a powerful bite, specially adapted to eating tough vegetation?
(a) Australopithecus (Paranthropus) robustus; (b) Homo ergaster; (c) Homo
sapiens; (d) Homo erectus.
9.Which hominin do scientists believe was the first to make stone tools? (a) Homo
habilis; (b) Homo erectus; (c) Homo sapiens; (d) one of these.
10.Which of the following trends seen in Hominin fossils over time is not correct? (a)
The hominin becomes taller and has a more erect posture. (b) The pelvis becomes
longer and narrower for attachment of walking muscles. (c) The foot forms more of a
platform with a rigid shape. (d) The big toe comes into line with other toes, i.e. not
opposable.
11.The oldest stone tools discovered so far that were made by our ancestors are: (a)
4.6-million years old; (b) 2.6-million years old; (c) 1.6-million years old; (d) 0.6-million
years old.
12.Which hominin species has the biggest brain? (a) Homo

sapiens; (b) Australopithecus africanus; (c) Australopithecus afarensis; (d) Homo
erectus.
13.The loss of cranial crests in hominids over time represents: (a) a reduction in the
protection of eye orbits. (b) a reduction in the size of the muscles that support the head.
(c) a de-emphasis on heavy chewing. (d) a reduction in protection of the brain.
14.Blombos Cave has the world’s oldest artefacts and art which include: (a) shell beads,
a gold rhino and engraved ochre. (b) engraved ochre, shell beads, stone tools. (c) iron
arrow heads, stone tools, clay pots. (d) stone tools, clay pots, glass beads.
530
[14]
2. Terms
1.The species of Homo that appeared about 200 000 years ago.
2.A stone tool that has been flaked on two faces or opposing sides.
3.Any animal that walks only on two legs.
4.The opening of the skull through which the spinal cord leaves the brain.
5.The space in the tooth row that allows the canine of the lower jaw to slide past
the third premolar in apes and early hominids.
6.The tribe (or group) to which Australopithecus and Homo belong.
7.The species of Homo that has a flattened face, prominent chin and dome-
shape skull.
8.The outward projection of the face in hominoids.
9.Tear-drop shaped stone tools associated with Homo erectus and

archaic Homo sapiens (Homo heidelbergensis).
[9]
3. Mix and match
Match each description in Column A with an item in Column B. Write the letter next to
the relevant number.
1.broad, shallow pelvis A.Animals adapted to life in the trees
2.parabolic dental arch B.98.5 % of same genes as Homo sapiens
3.chimpanzee C.Used to determine ancestry of races
531
4.arboreal D.Possibly the earliest hominin genus (4.4 – 5.6
mya)
5.Ardipithecus E.Shape of Homo dental arch
6.mtDNA. F.Brains expand and cheek teeth get smaller
7.Homo ergaster G.Probable user of stone hand axes and cleavers
8.evolution of H.Feature of bipedalism

hominins
[8]

word word
1.Australopithecus africanus has a large, complex brain

capable of creative thought, language, making of
symbols.
2.Homo sapiens’ success over the other Homo species

was probably due to their good hunting skills, which
greatly improved their carbohydrate intake, leading to
stronger bodies and bigger brains.
3.Homo sapiens is today the only living hominin.
4.A large brain was not considered to be a big

advantage during times of dramatic climate change.
5.The Homo species were carnivores, which enabled

them to eat both plants and animals making them very
adaptable to a variety of habitats.
532
6.Although the world has a vast number of different
human races we all share 99.9 % of the same DNA.
7.The species name ‘habilis’ means ‘hard worker’.
8.Features that show an animal is bipedal include a

foramen magnum that is further forward and a narrower
pelvis.
9.The forehead of Homo sapiens was much steeper

than that found in Homo ergaster, which hinted at
increased brain size.
10.Apart form fossil evidence, archaeological evidence

points to Homo sapiens originating in Africa about 180
000 years ago.
11.Homo neanderthalensis is the direct ancestor of

modern humans.
12.Homo habilis and African Homo erectus co-existed,

from about 2 mya to 1.6 mya.
13.Modern humans have small faces tucked under

small brain cases.
14.The earliest users of Oldowan or pebble tools

were Homo erectus.
15.DNA shows that our species and chimpanzees

diverged from a common ancestor that lived about 6
million years ago.
[15]
statement.
533
Items Statements Answer
1. 1.only species with the freedom A.Characteristics of Homo sapiens

to say ‘No’
2.is a problem solver
2. 1.Blombos caves B.Engraved ochre tablets found here
2.Sterkfontein caves
3. 1.longer, narrower pelvis C.Aids bipedal walking
2.divergent big toe
4. 1.Homo erectus D.Moved out from Africa about 60

000 years ago
2.Homo habilis
[4]
Total [50]
Homo ergaster caught faster prey with improved stone tools
NO
4.5 Evolution in present times
In our modern world, evolutionary principles have become very relevant and are used
for example in:
534
Resolving legal issues, by ‘DNA fingerprinting’.
Tracing evolutionary origins of diseases and developing treatments.
Selective breeding of plants and animals.
Understanding resistance of insect pests to insecticides.
Modern warfare, by the use of biological pathogens and mutation-inducing chemicals.
Is evolution happening now?
Evolution is always happening, but for many species, including humans, it occurs
extremely slowly over thousands of years, which makes it difficult, if not impossible, to
observe. However, evolutionary change can be:
demonstrated in a laboratory using rapidly reproducing life forms such as single-celled

organisms and certain invertebrates. See the examples below.
seen as a result of the breeding of new varieties of plants and animals by artificial
selection.
noticed in a situation where resistance:
–to TB drugs developed in the TB bacterium
–to an insecticide developed in insects.
seen in the alarming adaptation of HIV to drugs.
shown by development of new species of plants by polyploidy and hybridisation.
Why can the use of antibiotics and insecticides be risky?
Populations of pathogenic organisms, e.g. bacteria and insects can evolve quickly as:
they have natural variation.
mutations occur often because the individuals breed very rapidly.
In the process of evolving they can gain resistance to many chemicals that should kill
them. The antibiotics or insecticides therefore cease to be useful.
1. Resistance to antibiotics in bacteria
535
Antibiotics are important medicines as they help fight infections caused by bacteria. The
incorrect use of antibiotics, however, has become a serious threat to public health. This
is because bacteria can develop resistance to the antibiotic, making it ineffective. For
example, once-powerful drugs such as penicillin have become ineffective against new
drug-resistant bacterial strains, such as those that cause tuberculosis and
staphylococcal infections. As a result, the incidence of these once-controllable
infections is steadily increasing.
Antibiotic resistance is a serious problem in hospitals as some bacteria are now

resistant to almost all known antibiotics. These bacteria, which carry several resistant
genes, are called multi-drug resistant or, informally, ‘superbugs’.
Antibiotic resistance is the ability of bacterium to survive the effects of antibiotics and
to continue living and reproducing.
How does resistance develop?
A typical scenario is as follows:
A person with a bacterial infection starts a five-day course of antibiotics – a period

calculated to be long enough for all bacteria to be destroyed either by the antibiotic or
by the body’s immune system.
What often happens, however, is that after three days the person feels well and stops
taking the antibiotic. Bacterial resistance to the antibiotic can now develop as follows.
–Due to natural variation (which exists in all populations) and chance mutations
(common in rapidly producing populations) some bacteria have a ‘new’ gene that offers
resistance to the antibiotic. These will survive the initial doses of the antibiotic.
–As bacteria reproduce rapidly the bacteria with the resistant gene could soon form a
new antibiotic-resistant population. In the course of 12 hours one bacterium can multiply
to become a billion.
Therefore, using an antibiotic incorrectly can cause the rapid evolution of an antibiotic
resistant bacterial strain.
536
Learning activity 1
Antibiotic resistance developed by natural selection
The process of natural selection resulting in evolution can be easily demonstrated over
a 24-hour period in a laboratory Petri dish, using bacteria in a nutrient medium.
Evolution of antibiotic resistant bacteria
Fill in the missing words in the text below.
There is genetic 1. __________________ among the individuals in a colony of bacteria.

This is partly caused by random mutations (as happens in all populations).
A dose of antibiotic is added to the Petri dish. Thus the 2. __________________

changes. As a selection force (environmental pressure) is introduced, bacteria with less
3. __________________ characteristics die off. A few bacteria with more 4.
__________________ characteristics survive because they are adapted to the new
environment. They are mainly the ones that will reproduce. Thus the 5.
__________________ characteristic is passed on and eventually the 6.
__________________ of the population will have an altered 7. __________________.
8. __________________ proposed the theory of evolution by natural selection, which

underlies the development of antibiotic resistance in bacteria.
Total [8]
How have resistant strains of TB developed?
As you will have learnt in Grade 11 tuberculosis (TB) is a chronic bacterial

infection caused by Mycobacterium tuberculosis (also called the TB bacillus).
Pulmonary TB in South Africa is of extreme concern as the number of cases keeps
increasing, especially as so many people have HIV/AIDS.
Treatment for TB in the form of antibiotics was first developed about 50 years ago and
the incidence, frequency and mortality rates of humans with TB declined sharply.
However, over time TB has become more common again.
This is because many patients fail to complete the full course of antibiotic treatment and
resistant TB bacteria survive. In terms of the process of evolution, the antibiotic exerted
an environmental pressure on the TB bacilli. Due to natural genetic variation that exists
537
in all populations, some TB bacteria were resistant (less susceptible) to the effect of the
antibiotic. This results in resistant TB bacilli surviving the shortened treatment. They
would then pass on this trait of antibiotic resistance to their offspring and soon most
bacteria would be resistant and the patients would inevitably develop TB again.
The resistant TB bacillus was increasingly forming the major part of TB populations. To
manage this problem, TB patients were given two medications simultaneously. This was
done in the hope that the TB bacillus would not develop resistance to both drugs at the
same time.
However, as improbable as it seemed, this did happen, and multi-resistant TB bacteria

evolved, causing the emergence of multidrug-resistant TB (MDR-TB).
MDR-TB is particularly dangerous because it can give rise to extensively drug-

resistant TB (XDR-TB), which requires aggressive treatment using a combination of
five different drugs. XDR-TB is very dangerous and is often fatal.
The emergence of MDR-TB and XDR-TB is a direct consequence of incomplete

treatments and evolutionary processes. Lack of human discipline created an
environment that selected for the survival of drug-resistant mutant TB bacteria.
2. Resistance to insecticides in pest insects
Pest insects can cause huge problems to humans as they:
destroy food crops, e.g. locusts
act as vectors of disease-causing pathogens, e.g. mosquitoes.
To manage these problems, scientists have developed various insecticides to destroy

the insects. However, it has repeatedly been found that a particular insecticide will not
be effective for long as the pest insects become resistance to it. As a result, crop losses
increase and diseases like malaria become extremely difficult to control.
By 1990, more than 500 species (including 114 kinds of mosquitoes) had acquired
resistance to at least one pesticide each. What happens then? Another poison is
developed, and then another, and so the cycle continues.
How did resistance to the insecticide DDT develop in insects?
DDT, a strong nerve poison, was widely used to:
kill the pest insects of crops in agriculture and forestry.
538
control some human diseases which have specific insect vectors, e.g. malaria, that is
transmitted by mosquitoes.
The use of DDT was initially very effective. Resistance to the poison, however,
developed in the following way:
Like all populations, the insect population has genetic variability. A few individuals have
a trait that allows them to detoxify DDT, making them resistant to the poison.
DDT, a selective force, selects for survival those insects with this favourable trait. This
trait is passed on to succeeding generations. As insects breed quickly, the genes for
resistance spread rapidly among the insect population.
With repeated use of DDT, new DDT-resistant populations with an altered genotype,
develop.
This is another good example of evolution by natural selection – the best adapted are
selected for survival while the less adapted die.
Note:
Because of widespread environmental contamination and resultant ecological threats

posed by DDT and its breakdown products, most industrialised countries banned its use
in the early 1970s. Once the selective pressure (DDT) was removed, insect populations
that are not resistant to DDT have re-emerged. For this reason, in South Africa,
renewed spraying with low-dosage DDT is again proving effective against the malaria
mosquito.
Learning activity 2
Insecticide resistance
Complete the diagrams so that they show how insecticide resistance develops. Your
labels must be relevant to evolution by natural selection:
Total [8]
To end off with ….
A few years ago the World Health Organization published this anonymous bit of
doggerel titled ‘The History of Medicine.’
539
540

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LIFE SCIENCES

Science indicates it is necessary to use certain methods in our study of the

We approach this using careful methods that can be copied by others.

o % proposing hypotheses (the predicted outcome of an

o % carrying out investigations and experiments to test these

Scientific knowledge changes over time as more is discovered and understood

Why choose Life Sciences as a subject?

% provide an awareness of the ways biotechnology and a knowledge of Life

% build an appreciation of the unique contribution of South Africa to Life Sciences -

Life Sciences Strands for Grade 12

Knowledge Strand 1: Life at a Molecular, Cellular and Tissue Level

Knowledge Strand 2: Life Processes in Plants and Animals

Knowledge Strand 3: Diversity, Change and Continuity

The Purpose of studying Life Sciences

There are three broad purposes, which will expand as we continue:

Aim 1 - knowing the content (theory);

Aim 3 - understanding the applications of Life Sciences in society - both present

Aim 1: Knowing the content of Life Sciences

Learning content involves understanding and making meaning of scientific ideas,

Aim 2: Doing practical work and investigations

During a practical investigation it is important for you to be able to make

Planning an experiment would begin with identifying a problem, and then

Aim 3: Understanding the history, importance and modern applications of Life

Our search of knowledge is shaped by our world view. Therefore, an important

A final word on using this textbook

Remember, good learning begins in the classroom so always pay

Take note of sections you do not understand and revisit them

Ask questions to make sure you understand

Practice re-sketching the given diagrams

 How it should be used

Population and community ecology

Population ecology is concerned with fluctuations in the size of a population and

Individuals live together in populations. Different populations together

An ecosystem is made up of groups of different species of organisms that

An organism is an individual form of life, such as a bacterium, protest,

A community is a group of different species that inhabit and interact in a

A species is a group of closely related organisms that are very similar to

An individual is a single organism capable of independent existence.

A population is a group of organisms of the same species that occupy

What affects the size of a population?

Natality – birth rate in animals or the production of seeds in plants

Mortality – death rate

Immigration – individuals move into a population and stay

Emigration – individuals leave a population and do not return

For humans the:

birth rate is the number of births per 1000 people in a year.

Populations will therefore:

grow when birth and immigration exceed death and emigration.

decline when death and emigration exceed birth and immigration.

In a closed population, with no immigration or emigration, the only parameters

Learning activity 1 Population parameters

How is the growth of a population regulated?

If a few individuals enter an unoccupied area where there is no shortage of

exponential = increasing more and more rapidly

environmental resistance = the total number of factors that stop a

Eventually a balance is reached and the population stabilizes at a

The population fluctuates around the carrying capacity until the

The population size in an ecosystem is self-regulating. All negative-

Graph to show carrying capacity