Important Questions for Class 12

Biology
Chapter 7 – Evolution

Very Short Answer Questions 1 Mark

1. Name one fish-like reptile that evolved from a land reptile about 200 million
years ago?
Ans: Ichthyosaurs are fish-like reptiles that evolved from land reptiles about 200
million years ago.

2. For a long time, it was believed that life originated from decaying matter.
What is this theory known as? Name the scientist who experimentally disproved
this theory.
Ans: According to the theory of spontaneous generation life originated from
decaying matter however, Louis Pasteur disproved the theory.

3. If the abiotic origin of life is in progress on a planet other than earth, what
should be the conditions there?
Ans: If the abiotic origin of life is in progress on a planet other than earth then,
extreme high temperature, volcanic storms, reducing atmosphere containing CH 4,
NH3, H2, and water vapors should be the key conditions there.

4. Name the person who proposed that population tends to increase

geometrically while food production increases arithmetically.
Ans: Thomas Malthus proposed that population tends to increase geometrically
while food production increases arithmetically

Class 12 Biology www.vedantu.com 1

5. Name the scientist who had also come to a similar conclusion as that of
Darwin about natural selection as a mechanism of evolution. Which place did
he visit to come to conclusions?
Ans: Alfred Wallace was a naturalist and worked in the Malay Archipelago. He also
came up to a similar conclusion as that of Darwin about natural selection as a
mechanism of evolution.

6. Name any two vestigial organs found in the human body?

Ans: Vermiform appendix, wisdom teeth are the two vestigial organs found in the
human body.

7. What is the cause of speciation according to Hugo De Vries?

Ans: Mutations are the cause of speciation according to Hugo De Vries.

8. Name the phenomenon by which rapid speciation takes place?

Ans: Genetic drift is the phenomenon by which rapid speciation takes place.

9. Name the two scientists who set up a special experiment to prove Oparin’s
theory of the origin of life?
Ans: Urey and Miller were the two scientists who set up a special experiment to
prove Oparin’s theory of the origin of life.

10. Name the common ancestor of apes and man?

Ans: Dryopithecus is the common ancestor of apes and man.

11. Which period is known as the “Age of amphibians”?

Class 12 Biology www.vedantu.com 2

Ans: The Carboniferous period is known as the “Age of amphibians”.

12. What provided energy for abiotic synthesis on primitive earth?

Ans: Very high temperatures due to lightning or UV – rays provided energy for
abiotic synthesis.

13. Who showed that life comes from pre-existing life?

Ans: Louis Pasteur showed that life comes from pre-existing life.

14. What is meant by Gene pool?

Ans: Gene pool refers to the total of different kinds of genes pooled by all the
members of a population.

15. Which period is called the “Age of Reptiles”.

Ans: The Jurassic period is called the “Age of Reptiles”.

16. Name the species of human beings which is most closely related to modern
man.
Ans: Cro-magnon is the species of human beings that are most closely related to
modern man.

17. What is the “Founder’s effect”?

Ans: Sometimes a change in frequency of an allele is so different in the new sample
of a population that they become a whole new species altogether hence, the original
drifted population becomes founder and this effect is known as the Founder’s effect.

Class 12 Biology www.vedantu.com 3

Short Answer Questions 2 Marks

1. Explain the Oparin-Haldane theory of the chemical evolution of life.

Ans: The first life form could have come from pre-existing, non-living organic
molecules (such as the RNA, Proteins) and the formation of life was preceded by
chemical evolution. This theory suggests that life arose gradually from inorganic
molecules, with amino acids working as the building blocks. These then combine to
make complex polymers that might get assembled into structures that were capable
of sustaining and replicating themselves. Oparin considered these as colonies of
proteins that clustered together to carry out metabolism, whereas, Haldane thought
of them as macromolecules that were enclosed in membranes to build up cell-like
structures.

2. Distinguish between convergent and divergent evolution giving one example

of each.
Ans: The difference between convergent and divergent evolution are as following:

Divergent Evolution Convergent Evolution

Development of different functional Development of similar adaptive

structures from a common ancestral functional structures in unrelated
form. Homologous organs show this groups of organisms. Analogous organs
type of evolution. show this type of evolution.

Examples: Darwin's Finches. Examples: Many aquatic vertebrates

and wings of insects, birds, and bats.

3. What is adaptive radiation? Explain with an example.

Ans: Adaptive radiation is defined as an evolutionary process producing new species
from a single, rapidly diversifying lineage. This process occurs due to natural
selection. Example: Darwin finches, found in Galapagos Island. A variety of finches

Class 12 Biology www.vedantu.com 4

present in Galapagos Island arose from a single species, which reached this land
accidentally. As a result, innumerable new species evolved, diverged, and adapted
thus occupying new habitats. These finches developed diverse eating habits, and
various kinds of beaks suiting their feeding habits.

4. How did Louis Pasteur disprove spontaneous generation theory?

Ans: Louis Pasteur showed that in pre-sterilized flasks, life did not originate from
killed yeast whereas, in the other flask which was open to the air, new organisms
originated from the dead yeast.

5. Define homologous organs? Give one example of an organ homologous to the

hand of man?
Ans: Homologous organs are the ones that are similar in their basic structure and
embryonic development but function differently. Example: Bones of forelimbs of
whales, bats, birds, and humans.

6. What is the role of variation in evolution?

Ans: Variations are important for the survival of species in any environment. If a
population of reproducing organisms are suited to a particular niche and if it gets
altered, the population could wipe out; however, with certain variations, they can
survive in the changing environment as well.

7. Describe one evidence that decisively proves that birds have evolved from
reptiles?
Ans: The missing link between birds and reptiles is the evidence that proves that
birds have evolved from reptiles. Archaeopteryx showed that “Birds evolved from
reptiles”. These are organisms that show characteristics of both birds (such as the
presence of wings, feathers in the body) as well as of reptiles (jaws with identical
teeth, etc).

Class 12 Biology www.vedantu.com 5

8. What is the study of fossils called? Mention any three points how the fossils
throw light on past life?
Ans: The study of fossils is known as paleontology. It has been concluded that fossils
throw light on past life as:

 A cross-section of Earth’s crust shows the arrangement of sediments one over

another.

 Each sediment contains different life forms which most probably got extinct
during the formation of particular sediment.

 Connecting or missing links contain characters of different groups.

9. Why has natural selection not eliminated sickle–cell anemia?

Ans: Sickle cell anemia is not eliminated during natural selection as in some cases,
SCA is beneficial since it provides a natural defense system against malarial
parasites.

10. Life originated from the earth’s inorganic atmosphere in the post, but this
no longer happens today. Give two reasons?
Ans: Life cannot be originated in the present-day atmosphere because of the
following reasons:
(i) Temperature of the present-day atmosphere is much less than that of the primitive
atmosphere.

(ii) The present-day atmosphere is oxidizing and not reducing in nature due to the
presence of oxygen.

11. If you discovered a fossil bird with scales on the body and teeth in the beak.
What would you conclude about its position in the animal kingdom?

Class 12 Biology www.vedantu.com 6

Ans: Since the fossil bird shows both avian and reptilian characters, such as scales
on the body and teeth in the beak hence, it is more likely to be considered as a
connecting link between the reptiles and the birds.

12. What is speciation? List any two events that lead to speciation?
Ans: Speciation refers to the origin of new species or phenomena of development of
new species from pre-existing ones.

The two events which lead to speciation are – Genetic drift, mutation, and natural
selection.

13. Would you consider the wings of a butterfly and a bat as homologous or
Analogous and why?
Ans: Wings of butterflies and bats are said to be analogous because they originated
from different parts – for example, butterfly wings originated from skin, feathers and
in bats, wings originated from forelimbs; however, both of them perform the same
function which is flying.

14. Define natural selection? Who else along with Charles Darwin proposed it
as the mechanism of evolution?
Ans: Natural selection is a process of selection in nature in which individuals with
those characteristics which enable them to survive better in natural conditions would
outnumber others who are less adapted under the same natural conditions Alfred

Wallace also proposed the same mechanism of evolution and called it “survival of
fittest”.

15. A chimpanzee can hold objects by its hand and an elephant by the trunk.
Are these organs Analogous or homologous?

Class 12 Biology www.vedantu.com 7

Ans: These organs are analogous as they are performing the same function which is
holding objects but have originated from different parts, for example, forelimbs in
chimpanzees and nose in elephants.

16. Differentiate between convergent and divergent evolution?

Ans: The difference between convergent and divergent evolution is as follows:

Divergent Evolution Convergent Evolution

It is the evolutionary process of different It is the form of evolution in which
species producing new species diverged more than one adaptive radiation occurs
from a single ancestral form in an isolated geographical area

Example: Australian marsupials Example: Camels are found in Asia and

Llamas are found in South America

17. Bring out differences between De Vries mutations and Darwinian

Variations?
Ans: The difference between De Vries mutations and Darwinian variations are:

De Vries mutations Darwinian Variations

Mutations are heritable changes in the Darwinian variations are gradual

characteristics of a population that arise and occur due to variations over
suddenly and cause speciation. several generations.

Mutations are random, directionless. Variations are small and

directional.

Short Answer Questions 3 Marks

1. (i) State the Hardy-Weinberg principle.

Class 12 Biology www.vedantu.com 8

Ans: According to the Hardy-Weinberg principle, the allele frequency in a
population is stable and constant from generation to generation.

(ii) When there is a disturbance in the Hardy-Weinberg equilibrium, what

would it result in?
Ans: When there is a disturbance in the Hardy-Weinberg equilibrium, it would result
in evolution.

(iii) According to this principle, what is the total of all allelic frequencies?
Ans: According to this principle, what is the total of all allelic frequencies is one.

2. Classify the following as examples of homology and analogy

(i) Hearts of fish and crocodile
Ans: The hearts of fish and crocodiles are an example of homology.

(ii) Wings of butterflies and birds

Ans: Wings of butterflies and birds are an example of an analogy.

(iii) Eyes of Octopus and Mammals

Ans: The eyes of Octopus and Mammals are an example of analogy.

(iv) Tubers of potato and Sweet potato

Ans: Tubers of potato and Sweet potato is an example of analogy.

(v) Thorns of Bougainvillea and spines of Opuntia

Ans: Thorns of Bougainvillea and spines of Opuntia is an example of analogy.

(vi) Thorn of Bougainvillea and tendrils of cucurbits.

Ans: Thorn of Bougainvillea and tendrils of cucurbits is an example of homology.

3. Stanley Miller and Harold Urey experimented by recreating in the laboratory

the probable conditions of the atmosphere of the primitive earth.

Class 12 Biology www.vedantu.com 9

(i) What was the aim of the experiment?
Ans: Stanley Miller and Harold Urey experimented by recreating in the laboratory
the probable conditions of the atmosphere of the primitive earth. The experiment
aimed to prove Oparin's theory of the origin of life.

(ii) In what forms was the energy supplied for chemical reactions to occur?
Ans: Electric discharge using electrodes.

(iii) For how long was the experiment run continuously? Name two products
formed.
Ans: One week; amino acids and sugar.

4. Study the figures given below and answer the following question.

i) Under the influence of which type of natural selection would graph (a)
become like the graph (b).

ii ) What could be the likely reason for new variations arising in a population.

iii) Who suggested natural selection as the mechanism of evolution?

Ans:
(i) Graph (a) would become like the graph (b) under the influence of the
disruptive and elective type of natural selection.

Class 12 Biology www.vedantu.com 10

 (ii) Because individuals at the extremes contribute more offspring compared
to those in the center and produce two peaks in the distribution of a trait
which leads to new variations arising in a population.
(iii) Charles Darwin suggested natural selection as a mechanism of evolution.

5. Fill up the blanks left in the table showing Era, period, and organism.

Era Period Organisms

Cenozoic A Modern man, mammals, birds, the rise of monocot

B Tertiary Rise of first Primate, angiosperm

Mesozoic C Gingko, Gnetales

D Jurassic Conifers, cycads, Reptiles

Paleozoic E Early reptiles (extinct)

F Silurian Psilophyton

Ans. (A) Quaternary (B) Cenozoic (C) Cretaceous (D) Mesozoic (E) Carboniferous
(F) Paleozoic

6. (i) In which part of the world, the Neanderthal man lived?

Ans: The Neanderthal man lived near Eastern and Central Asia

(ii) What was his brain’s capacity?

Ans: Their brain capacity was 1400 c.c.

(iii) Mention the advancement which Neanderthal man showed over

Homoerectus.
Ans: The advancements were:
 More brain capacity
 Use of hides to cover body

Class 12 Biology www.vedantu.com 11

  Burial of the dead.

7. Figures given below are of Darwin’s finches?

Variety of beaks of Darwin's finches.

(a) Mention the specific geographical area where these were found.
(b) Name and explain the phenomenon that has resulted in the evolution of such
diverse species in the region.
(c) How did Darwin visit the particular geographical area?
Ans: (a) Galapagos Island.
(b) Adaptive radiation - The process of evolution of different species in a given
geographical area starting from a point and radiating to other areas of geography
(habitats) is called adaptive radiation.
(c) Through sea voyage in a sailing ship called H.M.S. Beagle.

8. Give examples to show evolution by anthropogenic action.

Ans: Excess use of herbicides pesticides etc. has resulted in the selection of resistant
varieties on a much lesser time scale. The same is true for antibiotic or drug-resistant
microbes.
Examples of pesticides are- Aldrin, Methomyl, and examples of herbicides are
Acetochlor, Dinosep.

Class 12 Biology www.vedantu.com 12

9. By taking industrial melanism as an example, explain the concept of natural
selection by evolution?
Ans: Natural selection is a mechanism through which populations of living creatures
adapt to changes to survive. It claims that because of the survival of the fittest,
species evolve rapidly. Minimal differences are preserved and transmitted, giving
rise to new forms over time.

A collection of moths was discovered in the year 1850. White-winged moths

outnumbered dark-winged moths in this collection. The population of dark-wringed
moths rose with industrialization. The explanation for this is because, throughout the
post-industrial period, tree trunks became darkened by industrial smoke, preventing
the white-winged moth from surviving. However, it is also known that before
industrialization, trees were coated with thick growths of off-white-colored lichens,
allowing white-winged moths to thrive while dark-colored moths were easily
identified by predators. As a result, it may be argued that nature chooses the best
species for the job.

10. Who were the two scientists that experimented to synthesize organic
molecules abiotically? How did they provide the probable condition of the
primitive earth in this experiment?

Class 12 Biology www.vedantu.com 13

Ans: Urey and Miller tried to create in the laboratory similar conditions which might
have existed in the early primitive atmosphere. A mixture of water vapors methane,
ammonia, and hydrogen is exposed to electric discharge in a closed chamber, this
fluid thus formed is allowed to stand for several weeks as a result, amino acids e.g.
glycerine and alanine are formed from the fluid. They suggested that electric
discharge produced during lightning in the primitive atmosphere of the earth might
have resulted in the formation of organic compounds.

11. What is Biogenetic law? How comparative embryology does provide

evidence for evolution?
Ans: It has become evident from embryological studies that there was one
developmental pattern. In all organisms, life begins with a unicellular structure. The
embryos of fish, frog, turtle, bird, and man resemble one another so closely that it
becomes difficult to distinguish them.
Mammalian embryo passes through fish–like, amphibian-like, reptiles like and bird-
like stages during the development of an organism (ontogeny), some of the
evolutionary steps (phylogeny) are repeated in different groups of organisms. This
leads Ernst Haeckel to formulate a famous theory – “Recapitulation Theory /
Biogenetic Law which states that “Ontogeny recapitulates phylogeny” The sequence
of embryonic development shows striking similarity e.g. appearance of gill cleft and
notochord in embryonic development of all vertebrates from fish to man.

12. Chemical insecticides remain useful only for a limited time. Explain
concerning evolution with a suitable example.
Ans: Chemical pesticides are used in agricultural fields to get rid of various pests
and insects that cause crop loss. These chemical insecticides affect some of the pests
metabolic characteristics, resulting in the pest's death.

However, these pests develop immunity over time as a result of various generations.
Pests that are resistant to these insecticides are born as a result of mutations. These
insecticides will thereafter be useless. As a result, you should avoid using these
insecticides.

Class 12 Biology www.vedantu.com 14

13. What are the facts that support Darwin’s theory of Natural selection?
Ans: The following facts that support Darwin’s theory of Natural selection

1. Overproduction: - All organisms tend to multiply at a high rate but all organisms
can’t survive.

2. Struggle for Existence: - Because of limitation of space and food all the offspring
resulting in overproduction will not survive and they will compete with one another
to grow. This develops a struggle for existence not only among individuals of
different species but also among the same species.

3. Variations: No two individuals of the same species are exactly alike even coming
out from the same parental stock.
4. Survival of fittest: The individuals with useful variation will survive during the
struggle of existence while those with less fortunate variation would perish.

14. Trace the important events or stages of human development?

Ans: The common ancestor of apes and man is the primate Dryopithecus that lived
about 15 million years ago the human evolution is as follows:

1. Australopithecus: They are 4ft, with a brain capacity – 500 to 650 cc. They have
bipedal locomotion, are omnivorous, and have an erect posture. They used stone
weapons for hunting and lived in caves.
2. Homo Erectus: They showed an increase in brain size They are good hunters, ate
meat domesticate animals, and discover fire.

3. Netherlands man: They were short with heavy brows retreating forehead large
jaws and stooped postures They wore clothes, good hunters, and tool makers.

4. Cromagnonman: They were completely erect and 6 ft tall. He used bones as tools
and was a cave dweller. They are excellent tool makers and fine artists.

5. Homo sapiens: They have a brain capacity of 1450cc. and skull much thicker. His
intelligence has enabled him to adapt and control the environment. He started
agriculture.

Class 12 Biology www.vedantu.com 15

15. What are the three different ways in which selection may occur.
Ans: The three different ways in which selection may occur are as below:

(i) Stabilising selection: Individuals with an intermediate value of heritable

phenotypic characteristics are favored over other individuals.

(ii) Directional selection: Individuals with one extreme of heritable

phenotypic characteristics have an advantage over individuals in a
population.

Class 12 Biology www.vedantu.com 16

 (iii) Disruptive selection: individuals with either extreme or heritable
phenotypic characteristics have an advantage over individuals with
intermediate phenotypes.

16. State in what ways Stanley miller simulated the condition of :

i) Primitive atmosphere on earth.

Ans: A fluid containing a mixture of methane, ammonia, hydrogen, and water vapor
in a closed flask.

ii) Energy source at the time of origin of life.

Ans: Energy source during the origin of life was Sun. This energy is provided by
electric discharge using electrodes in this experiment.

iii) Formation of organic molecules of life.

Ans: The organic molecules which are formed during the experiment are amino
acids.

17. What Is Biogeography? How Darwin’s finches provide biogeographical

evidence in favor of evolution.

Class 12 Biology www.vedantu.com 17

Ans: The branch of geography which deals with the study of the pattern of
distribution of plants and animals is called Biogeography.

Example- Galapagos islands- Charles Darwin during his voyage found that animals
of these islands resemble those of South American islands. For example birds of
Galapagos Island also known as Darwin’s finches do not resemble birds of South
America therefore, he stated that finches were derived from ancestral stock that had
emigrated from the mainland to the island and underwent profound changes under
different environmental conditions.

18. How did Louis Pasteur successfully demolish the popular theory of
spontaneous generation?
Ans: Louis Pasteur used a special swan-necked flask for the experiment. He took a
mixture of sugar and yeast powder, filled it in the flask, then boiled it as a steady
current of steam rushed out from the S-shaped tube –causing the death of all
microorganisms. After this, the flask remained unchanged, however, when the neck
of the flask was cut-off, a thick growth of microorganisms was observed which
presumed that there are microorganisms that could not reach the flask in the initial
stage, however, in the second phase, they came in direct contact with the solution.

Long Answer Questions 5 Marks

1. What does Hardy Weinberg’s principle state? What are the factors which
affect Hardy Weinberg’s equilibrium?
Ans: A. to Hardy Weinberg’s principle, allele frequency in a population is stable
and is constant from generation to generation i.e. total gene pool remains constant.
This is called genetic equilibrium e.g. In a diploid organism, suppose ‘p’ represents
the frequency of allele ‘A’ and ‘q’ represents the frequency of allele ‘q’.

p 2  2pq  q 2  1

Factors affecting Hardy – Weinberg Equilibrium :

(i) Gene flow: When the migration of a section of a population to another

place starts, gene frequency changes in both the original as well as in the
new population.

Class 12 Biology www.vedantu.com 18

 (ii) Genetic drift: If by chance a particular allele frequency decrease or
increases in a population.
(iii) Mutations: They are sudden changes in the genotype which are carried
over a generation.
(iv) Genetic recombination: Sometimes changes in the frequency of an allele
are different in a new sample of the population as they become new
species.
(v) Natural selection: Process by which individuals with particular heritable
characteristics survive and reproduce at a higher rate than other individuals
favored by natural selection tend to be more common in the next
generation than in the parent generation.

2. How do Darwin and Hugo de Vries think about the Mechanism of Evolution?
Ans: Darwin: Darwinian variations are gradual, small, and directional Hugo
deVries: put forth the idea of mutations, mutations are sudden random and
directional

3. With the help of a suitable diagram, represent the operation of natural

selection on different traits.
Ans: Natural selection is a basic mechanism of evolution, along with mutation,
migration, and genetic drift.

Darwin's idea of evolution by natural selection is simple but misunderstood. To

know the same, consider a population of beetles:
1. There is variation in traits: Example, some beetles are green while others are
brown.

Class 12 Biology www.vedantu.com 19

2. There is differential reproduction: Since the environment can't support unlimited
population growth, not all individuals get to reproduce to their full potential. For
example, green beetles are eaten by birds and survive to reproduce less than brown
beetles.

3. There is heredity: The brown beetles which survive have brown baby beetles since
this trait has a genetic basis.

4. result: The more advantageous trait, brown coloration allows beetles to have more
offspring, thus it becomes more common in the population. If this continues,
ultimately all the individuals in the population would come out to be brown.

4. What does Oparin – Haldane hypothesis about the origin of life suggests.

Class 12 Biology www.vedantu.com 20

Ans: According to Oparin and Haldane’s Biochemical hypothesis, the origin of life
occurs in three stages.

The first life form could have come from pre-existing, non-living organic molecules
(such as the RNA, Proteins) and the formation of life was preceded by chemical
evolution. This theory suggests that life arose gradually from inorganic molecules,
with amino acids working as the building blocks. These then combine to make
complex polymers that might get assembled into structures that were capable of
sustaining and replicating themselves. Oparin considered these as colonies of
proteins that clustered together to carry out metabolism, whereas, Haldane thought
of them as macromolecules that were enclosed in membranes to build up cell-like
structures.

5. What is chemogeny?
Ans. Chemogeny or chemical evolution suggests that most of the primitive forms of
life would have been generated spontaneously from some inorganic matter as a result
of the action of special external forces e.g. electric charge, UV-light, etc.
1. Saturated and unsaturated hydrocarbons were feasted when temp cooled to 900
Celsius or even below this.

2. From hydrocarbons, small chain compounds of carbon, hydrogen, and oxygen are
formed which condense to form sugar.
3. Ketones and aldehydes condense, polymerizes to form fatty acids.

4. Ammonia, hydrocarbon, and water reacted to form amino acids.

5. Hot sea water rich in primary organic compounds reacted to form nucleotides.

6. What is biogeny?
Ans: Biogeny or biological evolution is a stage that consists of
i) Formation of nucleic acids by polymerization of nucleotides.

ii) Giant molecules of nucleoproteins tend to be aggregated in various combinations

to form large colloidal particles called coacervates.

Class 12 Biology www.vedantu.com 21

iii) The development of the plasma membrane resulted in the accumulation of
different substances inside coacervates and the occurrence of certain internal
reactions leading to the development of the cell.

7. What is Cognogeny?
Ans: Cognogeny involves the differentiation and diversification of living beings
from the simplest first living cell. The first organism that evolved was
chemoautotrophic bacteria which later converted to tree autotrophic bacteria
example- green algae.

Class 12 Biology www.vedantu.com 22