Cambridge IGCSE™

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BIOLOGY 0610/42
Paper 4 Theory (Extended) February/March 2024

1 hour 15 minutes

You must answer on the question paper.

No additional materials are needed.

INSTRUCTIONS
● Answer all questions.
● Use a black or dark blue pen. You may use an HB pencil for any diagrams or graphs.
● Write your name, centre number and candidate number in the boxes at the top of the page.
● Write your answer to each question in the space provided.
● Do not use an erasable pen or correction fluid.
● Do not write on any bar codes.
● You may use a calculator.
● You should show all your working and use appropriate units.

INFORMATION
● The total mark for this paper is 80.
● The number of marks for each question or part question is shown in brackets [ ].

This document has 20 pages.

DC (DE/SG) 328326/4
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1 Enzymes are catalysts.

not enzyme
(a) (i) Describe what is meant by the term catalyst.

Substance speeding up the rate of reaction by lowering it's

...........................................................................................................................................
activation energy.
...........................................................................................................................................
Without being changed , where it can be recycled/reused
...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [2]

(ii) Enzymes are proteins.

State the names of the chemical elements found in all proteins.

Carbon,hydrogen,oxygen and nitrogen

...........................................................................................................................................

..................................................................................................................................... [2]

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(b) Lipase is an enzyme found in the human digestive system.

Fig. 1.1 shows the effect of pH on the percentage activity of lipase.

100

80

60
percentage
activity
40

20

0
3 4 5 6 7 8 9 10 11
pH

Fig. 1.1

Describe and explain the change in percentage activity of lipase shown on Fig. 1.1.
Description:...................................................................................................................................................
As pH increases from 3.8 to 7, percentage activity of lipase enzyme increases
from 0% to ...................................................................................................................................................
100%
optimum pH...................................................................................................................................................
is 7 with maximum percentage activity ( 100%)
As pH continues to increase from 7 to 10.2, percentage activity of lipase
...................................................................................................................................................
enzyme decreases gradually from 100% to 0%
Explanation:...................................................................................................................................................
pH 7 is the optimum pH where lipase enzyme works best,
...................................................................................................................................................
where it's active site is complementary to the substrate ( lipids)
...................................................................................................................................................
so they fit and bind where maximum number of enzyme substrate complexes
are formed, ...................................................................................................................................................
catalyzing the break down of lipids into soluble fatty acids and glycerol.
...................................................................................................................................................

...................................................................................................................................................
As pH changes away from optimum (pH 7), the enzyme is partially denatured
where the shape of it's active site is changed
...................................................................................................................................................
so the enzyme is no longer complementary to it's substrate
...................................................................................................................................................
so the substrate can no longer fit into the active site
Few then no.............................................................................................................................................
enzyme substrate complexes are formed [6]

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(c) (i) Complete the word equation to show the substrate and products for lipase.

Lipids /Fats lipase Fatty acids + Glycerol

........................................ ........................................ ........................................
[2]

(ii) Lipase acts in the duodenum.

Explain how the body provides a suitable pH for lipase activity.

By neutralization...........................................................................................................................................
of acidic chyme to provide an optimum pH (alkaline) for lipase
which is done by bile salts produced by liver ( stored in gall bladder) then
...........................................................................................................................................
released into intestinal lumen .
which is also done by sodium bicarbonate salt ( sodium hydrogen carbonate )
...........................................................................................................................................
present in pancreatic juice which is produced by pancreas and released into
...........................................................................................................................................
intestinal lumen.
...........................................................................................................................................
So lipase can catalyze the breakdown of large insoluble fat molecules into
...........................................................................................................................................
small soluble fatty acids and glycerol in a chemical digestion process for
absorption. ..................................................................................................................................... [3]

[Total: 15]

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2 Fig. 2.1 shows a cross-section of a human heart.

Fig. 2.1

(a) (i) On Fig. 2.1, label with an R the position of the right ventricle. [1]

(ii) State the names of the structures labelled A and B on Fig. 2.1.
Bicuspid valve ( atrioventricular valve)
A ........................................................................................................................................

semilunar valve (pulmonic valve)

B ........................................................................................................................................
[2]

(iii) Complete the sentence about blood vessel C.

heart
Blood vessel C transports blood from the ................................................................ to the
body organs ( except lungs)
................................................................ .
[2]

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(b) Fig. 2.2 shows a cross-section of part of a heart that has an incomplete structure.

atria

incomplete
heart structure

Fig. 2.2

Explain how the incomplete heart structure shown in Fig. 2.2 may affect a person’s ability to
transport oxygen.
When the septum has an incomplete structure ,
...................................................................................................................................................
there is no separation between left side and right side ( left atrium and right
atrium) of the...................................................................................................................................................
heart
there is mixing between oxygenated and deoxygenated blood
...................................................................................................................................................
so there is less oxygen ( level/percentage concentration ) in blood pumped out
of heart from...................................................................................................................................................
left ventricle through Aorta to respiring body cells
so less oxygen( which is required for aerobic respiration) is delivered to
...................................................................................................................................................
respiring cells/tissues.
...................................................................................................................................................

............................................................................................................................................. [3]

less concentration gradient between blood and respiring cells so less diffusion rate of oxygen
into respiring cells

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(c) Fig. 2.3 shows how the body uses aerobic and anaerobic respiration during the first 120
seconds of vigorous physical activity. Between 0 and 20 seconds, the body also uses stored
energy.

100

80 aerobic respiration

60
percentage of
energy released
40

Percentage of energy released 20 anaerobic respiration

levels off from 100 to 120 seconds Maximum percentage of energy
for both aerobic and anaerobic released is the same for both
0
respiration but with less 0 20 40 60 80 100 120 (80%) but reached by anaerobic
percentage ( 20%) for anaerobic time / s respiration earlier ( at 20
respiration and higher percentage seconds) and later by aerobic
(80%) for aerobic respiration Fig. 2.3 respiration ( at 100 seconds)

(i) Describe the data shown in Fig. 2.3.

In aerobic respiration,
...........................................................................................................................................
As time passes from 0 to 100 seconds , percentage of energy released
increases from...........................................................................................................................................
10 % to 80 %.
Then as time continues to pass from 100 to 120 seconds, percentage of
...........................................................................................................................................
energy released levels off /remains constant/ reaches a plateau at 80%.
...........................................................................................................................................

In anaerobic respiration,
...........................................................................................................................................
As time passes from 0 to 20 seconds, percentage of energy released
...........................................................................................................................................
increases steeply from 4 % to 80%.
...........................................................................................................................................
Then as time passes from 20 to 100 seconds , percentage of energy released
decreases from...........................................................................................................................................
80 % to 20% ,then it levels off at 20 % from 100 to 120 seconds
At 60 seconds, percentage of energy released by both aerobic
..................................................................................................................................... [4]
and anaerobic respiration is the same (50%)
(ii) State the balanced chemical equation for aerobic respiration.

C H O + 6 O ----------> 6 CO + 6 H O
..................................................................................................................................... [2]

(iii) During anaerobic respiration an oxygen debt can build up.

State the name of the chemical that causes this oxygen debt.

Lactic acid
..................................................................................................................................... [1]

[Total: 15]

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3 (a) Fig. 3.1 shows a growing plant. The plant is growing in the dark.

plant shoot

soil

plant root

Fig. 3.1

(i) State the name of the growth response shown by the plant shoot in Fig. 3.1.
Negative gravitropism
..................................................................................................................................... [1]

(ii) Explain how the growth of the plant shoot in Fig. 3.1 is controlled.

By Auxins ( plant growth hormone) made of protein ,

...........................................................................................................................................
produced by ...........................................................................................................................................
growing tips of shoot mainly ( and root),
transported through phloem,
diffuses down...........................................................................................................................................
concentration gradient and accumulate in cells/ side of
shoot closer ...........................................................................................................................................
to gravity ( lower side )
causing water potential of cells to be lowered
...........................................................................................................................................
increasing water uptake by osmosis down water potential gradient
...........................................................................................................................................
through partially permeable membrane of shoot cells
.....................................................................................................................................
causing an increase in turgor pressure and cell elongation [3]
so shoot bends away from gravity.

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(b) Plant roots growing towards water is another growth response.

State two uses of water in a plant.

Support
1 ................................................................................................................................................
Transport of minerals/ salts
...................................................................................................................................................
Raw material for photosynthesis
Lost in transpiration for cooling and maintaining transpiration pull
2 ................................................................................................................................................
Solvent in cells for enzymes activity/metabolic reactions
...................................................................................................................................................
[2]

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(c) A student measured the root length of a bean seedling over a period of 120 hours.

Fig. 3.2 shows the results.

30

20

root length
/ mm
10

0
0 24 48 72 96 120
time / hours

Fig. 3.2

Calculate the percentage increase in root length between 48 hours and 96 hours.

Give your answer to two decimal places.

Space for working.

25 - 9
= __________ X 100
9

= ________
16 X 100
9
177.78
............................................................ %
= 177.777 = 177.78 [3]

[Total: 9]

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4 Fig. 4.1 shows the concentrations of female sex hormones during the menstrual cycle.

S
progesterone

R
concentration
of hormones
FSH

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28
day of menstrual cycle

Fig. 4.1

(a) Identify, from Fig. 4.1, hormone:

oestrogen
R .............................................................

LH
S. ............................................................
[2]

(b) State the day or days of the menstrual cycle shown in Fig. 4.1 when:

14
ovulation is most likely to occur ................................................................................................

1- 5/6/7
shedding of the uterine lining occurs. .......................................................................................
[2]

(c) Describe how the concentration of progesterone would change during pregnancy.

Give a reason for this change.

It would increases / continue to increase/ does not decrease
as it...................................................................................................................................................
keeps being produced by the placenta
For maintaining and thickening the endometrium ( uterine lining)
...................................................................................................................................................
To prevent miscarriage/abortion
To inhibit the release of FSH and LH to prevent maturation of follicles/egg
...................................................................................................................................................
cells and ovulation
...................................................................................................................................................
To prevent fertilisation and development of embryos of different age
............................................................................................................................................. [2]

(d) State the sites of production of progesterone during a menstrual cycle and during pregnancy.
ovaries ( by corpus luteum)
during a menstrual cycle ...........................................................................................................
placenta
during pregnancy ......................................................................................................................
[2]

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(e) Describe the role of FSH in the menstrual cycle.

-Stimulates the growth/development/maturation of follicles/egg cells
...................................................................................................................................................
-Stimulates the release of oestrogen by growing follicles
...................................................................................................................................................

............................................................................................................................................. [1]

[Total: 9]

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5 Fig. 5.1 shows part of a monkey flower plant.

Fig. 5.1

(a) (i) State two pieces of evidence, visible in Fig. 5.1, that show that monkey flower plants
are pollinated by insects.
Have large colourful petals
1 ........................................................................................................................................
Petals have spots
...........................................................................................................................................
for attracting insects
2 ........................................................................................................................................

...........................................................................................................................................
[2]

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(ii) The monkey flower plant in Fig. 5.1 reproduces sexually.

Describe the advantages and disadvantages of sexual reproduction for monkey flower
plants.
Advantages: ...........................................................................................................................................
Maintains genetic variation
...........................................................................................................................................
so less genetic diseases
more resistance to pathogens/ transmissible diseases
...........................................................................................................................................
more resistance to climate change/ changes in environment of parent plant
more chance of...........................................................................................................................................
fitness ,adaptation ,survival , evolution and natural selection.
Less risk of extinction
...........................................................................................................................................
Allows expression of recessive alleles
Allows expression of mutations
...........................................................................................................................................
Involves genetically different haploid sex cells formed by meiosis which allows
...........................................................................................................................................
restoring of diploid number upon fertilisation and prevents doubling of chromosomes
number over generations
...........................................................................................................................................

.....................................................................................................................................
Allows seed formation which are dormant and resist harsh conditions, [4]
which can then get dispersed and colonize new areas so reducing competition

Disadvantages:
-Two parents are required.
-More energy is required as both meiosis( for producing sex cells) and mitosis
(for growth and development of offspring)take place
-More time is required for growth and development of offspring.
-Genetic variation may result in undesired alleles/ features.
-May need two plants
-May need pollinating agents
-pollination/fertilization may not happen
-much pollen/ many seeds may be wasted

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(b) Monkey flower plants were introduced to Europe from North America about 200 years ago.

Scientists measured the leaf area of five monkey flower plants growing in Europe and five
monkey flower plants growing in North America.

Their results are shown in Table 5.1 and Table 5.2.

Table 5.1

plants growing in Europe

plant
leaf area / cm2
number
1 310
2 335
3 390
4 348
5 365
mean 350

Table 5.2

plants growing in North America

plant
leaf area / cm2
number
1 285
2 310
3 302
4 315
5 294
mean

(i) Using the data in Table 5.2, calculate the mean leaf area for plants growing in North
America.

Give your answer as a whole number and include the unit.

=____________________
285+310+302+315+294 ____=301.2
=1506 301 cm
................................................................
[2]
5 5
(ii) State a conclusion for the results shown in Table 5.1 and Table 5.2.

Mean leaf area for plants growing in Europe is more than mean
...........................................................................................................................................
leaf area of plants growing in North America
...........................................................................................................................................

..................................................................................................................................... [1]

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(iii) Ancestors of monkey flower plants had a much smaller leaf area.

Explain how the monkey flower plants have developed a larger leaf area over time.

-By mutation ( random change in sequence of bases of DNA )

...........................................................................................................................................
-caused by mutagens such as chemicals or ionizing radiations causing
...........................................................................................................................................
selection pressure.
...........................................................................................................................................
-So a new resistant allele is formed causing increased genetic variation
-Plants without the resistant allele die
...........................................................................................................................................

-Plants with the ...........................................................................................................................................

resistant allele ( having a selection advantage)
have a higher chance of fitness, adaptation , survival and natural selection
...........................................................................................................................................

...........................................................................................................................................
-They struggle, survive and reproduce passing their resistant allele to their
offsprings ...........................................................................................................................................
-(Mutation/ recessive allele is expressed by sexual reproduction)
...........................................................................................................................................
Resulting in evolution
...........................................................................................................................................

..................................................................................................................................... [5]

[Total: 14]

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6 (a) Fig. 6.1 shows part of the carbon cycle in the ocean.

Sun
carbon dioxide in
the atmosphere

ocean surface

phytoplankton

feeding
krill

krill faeces

zooplankton eating
krill faeces

Fig. 6.1 (not to scale)

(i) Phytoplankton contain chlorophyll.

Explain how phytoplankton lower carbon dioxide concentrations in the atmosphere.

-Chlorophyll can trap light energy which provides the activation energy
...........................................................................................................................................
needed for photosynthesis.
...........................................................................................................................................
-Where carbon dioxide gas, raw material for photosynthesis diffuses down
concentration...........................................................................................................................................
gradient into phytoplankton and reacts with water producing
oxygen and glucose ( light energy is converted into chemical energy)
...........................................................................................................................................

..................................................................................................................................... [2]

(ii) Suggest the role of zooplankton in this ecosystem.

consumer acting as a decomposer by digesting the organic matter in krill

...........................................................................................................................................
faeces
..................................................................................................................................... [1]

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(iii) State the names of two processes that add carbon dioxide to the atmosphere.

Respiration
1 ........................................................................................................................................
Combustion
2 ........................................................................................................................................
Decomposition [2]

(iv) Describe the effect on the environment of additional carbon dioxide in the atmosphere.

-Carbon ...........................................................................................................................................
dioxide is a green house gas which traps heat energy/ infra-red.
-causing an increase in atmospheric temperature.
-causing ...........................................................................................................................................
enhanced green house effect
-causing ...........................................................................................................................................
climate change resulting in melting of ice caps, increase in sea
level and...........................................................................................................................................
flooding.
causing habitat destruction, disruption of food chains, loss of biodiversity
...........................................................................................................................................
and increased risk of extinction.
...........................................................................................................................................

..................................................................................................................................... [3]

(b) Fig. 6.2 shows the pyramid of energy for a food chain in an ocean ecosystem.

Herbivore/2nd trophic level/1ry consumer

Fig. 6.2

(i) On Fig. 6.2, label the trophic level containing herbivores. [1]

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(ii) Explain why pyramids of energy usually have fewer than five trophic levels.

-As energy flow/transfer is inefficient where only 10% of energy flows.

...........................................................................................................................................
-While 90% of energy is lost.
...........................................................................................................................................
-Small percentage of energy from sun is fixed by plants in photosynthesis.
lost as radiations of heat energy/ in movement/ Don't forget to
-Energy maybe ...........................................................................................................................................
excretion/egestion. give many
...........................................................................................................................................
-Not all of the organism is ingested/digested examples on
energy loss
-Energy may be...........................................................................................................................................
lost to decomposers
-So less energy...........................................................................................................................................
would be available for higher trophic levels ( which have few
number of offsprings)
..................................................................................................................................... [3]

(iii) State two advantages of using a pyramid of energy rather than a pyramid of biomass to
represent a food chain.

1 -Indicates
........................................................................................................................................
how much energy is available in each trophic level
-Allows the comparison of ecosystems since not all
...........................................................................................................................................
organisms/biomass has the same energy content
2 ........................................................................................................................................

...........................................................................................................................................
[2]

(c) The oceans contain fish stocks that can be managed as a sustainable resource to provide
food for humans.

(i) State what is meant by the term sustainable resource.

-Renewable resource that does not run out

...........................................................................................................................................
-Can be easily and rapidly replaced if lost
...........................................................................................................................................
-such as replanting to replace forest trees
...........................................................................................................................................

...........................................................................................................................................

..................................................................................................................................... [2]

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not state (ii) Fishing can be managed to promote the conservation of fish stocks.
or suggest
Explain one way that fishing can be managed to conserve fish stocks.
( you need
to explain) -Raising education and awarness to
...........................................................................................................................................
prevent overfishing and fishing during breeding seasons
...........................................................................................................................................
-Regulating fishing methods so mesh size of nets is controlled
...........................................................................................................................................
and small fish are not caught.
...........................................................................................................................................
-International agreements/treaties and quotas
..................................................................................................................................... [2]
to ensure there is no overfishing
[Total: 18]

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