iG Biology - Question paper 2B ( Jun 2025)

Question 1

Read the passage below. Use the information in the passage and your own knowledge to answer the questions that follow.

Rivers – the arteries of the world

Rivers are important supplies of water for drinking, farming, industry, and leisure activities. Like our circulatory system, rivers are essential for transport, and have a homeostatic effect on nature. The biodiversity in rivers is high as they are the habitat for many different species. In many countries rivers are under threat from human impact, particularly the release of untreated sewage.

Flooding can cause untreated sewage to run into rivers from pipelines. Scientists estimated that in England and Wales during 2022, sewage was released into rivers for a total time of 300 000 hours. This sewage came from 1200 different pipelines. Untreated sewage may contain fertilisers, pesticides, pathogenic bacteria, and pharmaceutical drugs.

The photograph shows sewage being released into a river. The sewage causes the growth of something called ‘sewage fungus’. Sewage fungus looks like fungus but is a solid collection of several types of anaerobic bacteria. Sewage fungus is common in rivers that are polluted with untreated sewage or are near to cattle and intensive crop farms. If sewage fungus is found in a river it often indicates that the biodiversity of the river will be low.

Pesticides from agriculture are also released into rivers, and these are frequently transferred through natural food chains. Even pharmaceutical drugs, such as those containing the hormones oestrogen and progesterone, have been found in polluted rivers. These drugs must have been consumed by humans, excreted and then released into the sewage flowing into rivers.

Untreated sewage can also contain pathogenic species of bacteria that then enter rivers. If humans are infected with these bacteria, the large intestine absorbs less water, causing diarrhoea. Some of the bacteria found in sewage are resistant to antibiotics.

Scientists are looking for ways to prevent river pollution. One way is to reduce the risk of pollution from fertilisers and from cattle urine and faeces. Woodchip bioreactors are being trialled in agricultural fields that are near to rivers. These bioreactors are pits filled with woodchips and denitrifying bacteria. Water drains through these bioreactors, which helps to remove nitrates before they reach the rivers. In some countries, efforts are being made to replant forests in areas upstream of rivers to reduce river flooding and the risk of untreated sewage release.

(a) Rivers have a homeostatic effect on nature. This is similar to the role of homeostasis in humans.
State what is meant by the term homeostasis (lines 2 and 3).

(b) Calculate the mean number of hours that each pipeline released sewage into rivers in 2022 (lines 7 and 8).

(c)(i) Sewage fungus is not a fungus but is made from several different species of bacteria.
Which of these structures are present both in fungi and in bacteria?

A) cell wall and cytoplasm only
B) cell wall and nucleus only
C) cell wall, cytoplasm and nucleus
D) cytoplasm and nucleus only

(ii) Explain why rivers near to farms may have low biodiversity (lines 13 to 16).

(d) Oestrogen and progesterone in polluted water lower the levels of FSH and LH in mammals.

(i)State why lower levels of FSH can reduce fertility in mammals.
(ii) State why lower levels of LH can reduce fertility in mammals.

(e)(i) Pathogenic bacteria produce poisons that prevent the active transport of salt into the blood vessels surrounding the intestines.
Explain why preventing the transport of salt into the blood vessels will cause more water to be present in faeces (lines 22 to 24).

(ii) Explain why overuse of antibiotics has led to an increase in antibiotic-resistant bacteria (lines 24 and 25).

(f)(i) Explain how woodchip bioreactors reduce pollution in rivers (lines 27 to 31).
(ii) Explain why replanting forests in areas upstream of rivers will reduce flooding (lines 31 to 33).

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 3(j): Co-ordination and response — part (a)
• 5(d): Human influences on the environment — parts (c)(ii), (e)(ii), (f)(i), (f)(ii)
• 1(b): Variety of living organisms — part (c)(i)
• 4(a): Reproduction — parts (d)(i), (d)(ii)
• 2(d): Movement of substances into and out of cells — part (e)(i)
• 4(b): Inheritance — part (e)(ii)

▶️ Answer/Explanation

Solution

(a) An answer that makes reference to one of the following points:
• maintenance of constant (internal) conditions in body / eq (1)
• control / regulating / maintaining internal conditions / eq (1)
• control / regulating / maintaining internal environment / eq (1)
• keeping conditions in body the same / within a (narrow) range / eq (1)

(b) • 250 (1)
Calculation: \( \frac{300000}{1200} = 250 \)

(c)(i) A (cell wall and cytoplasm only)
B is not the answer as bacteria do not have nuclei
C is not the answer as bacteria do not have nuclei
D is not the answer as bacteria do not have nuclei

(c)(ii) An explanation that makes reference to the following points:
1. fertilisers / animal waste / minerals / nitrates / phosphates (run off / leach) / eq (1)
2. algal growth / eutrophication / eq (1)
3. less light (penetrates) / competition for light / less photosynthesis / eq (1)
4. decomposition / decay (of dead algae / plants / organisms / organic waste / manure / faeces / sewage) eq (1)
5. less oxygen / only anaerobic species grow / eq (1)
6. bacteria respire / other species cannot respire / reduced respiration / eq (1)
7. pesticides kill organisms / eq (1)

(d)(i) An answer that makes reference to one of the following points:
• eggs / ova / follicles, do not mature / do not grow / eq (1)
• (FSH is required to) mature eggs / ova / follicles (1)
• (low FSH leads to) less oestrogen / (FSH) stimulates oestrogen release (1)

(d)(ii) An answer that makes reference to one of the following points:
• no ovulation occurs / egg not released / ova not released / eq (1)
• LH / it stimulates ovulation / LH / it stimulates egg release / eq (1)
• (lower LH leads to) less progesterone / LH / it stimulates progesterone (1)

(e)(i) An explanation that makes reference to two of the following points:
• less water absorbed / less water enters blood / less water enters capillaries / eq (1)
• (water moves by) osmosis (1)
• water potential in blood is high(er) / water potential in gut / faeces / lumen is low(er) / eq (1)

(e)(ii) An explanation that makes reference to three of the following points:
1. mutation (1)
2. (only resistant bacteria) survive / are not killed / non-resistant bacteria die / eq (1)
3. bacteria reproduce / multiply / eq (1)
4. pass on allele / gene / mutation / eq (1)

(f)(i) An explanation that makes reference to two of the following points:
• (denitrifying bacteria convert) nitrate into nitrogen (1)
• so less eutrophication / less algal growth / more oxygen in river / lower BOD / eq (1)
• wood chips have large surface area (for bacteria) / wood chips are biodegradable (so do not pollute) / eq (1)

(f)(ii) An explanation that makes reference to two of the following points:
1. trees / roots absorb water / trees intercept water / eq (1)
2. (more) transpiration (1)
3. less runoff / slows down water flow / more soil permeability / more infiltration / eq (1)
4. less soil erosion / roots hold onto soil / roots stabilise soil / eq (1)
5. rivers do not get blocked (with soil) / eq (1)

Question 2

The lungs and the kidneys are excretory organs.

(a) (i) Which substances are excreted by the lungs?

A) carbon dioxide and urea
B) carbon dioxide and water
C) carbon dioxide, urea, and water
D) urea and water

(ii) The graph shows how the volume of air in the lungs changes over time.

Explain the change in volume of air in the lungs from point X to point Y.

(b) People with a condition called diabetes often have very high blood sugar.

Urine from people with diabetes attracts ants but urine from people without diabetes does not attract ants.

Ants are insects that are attracted to glucose.

Explain why people with diabetes produce urine that can attract ants.

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 3(i): Excretion — part (a)(i)
• 2(g): Gas exchange — part (a)(ii)
• 3(i): Excretion — part (b)
• 3(h): Transport — part (b)

▶️ Answer/Explanation

Solution

(a)(i) B (carbon dioxide and water)
A is not the answer as lungs do not excrete urea
C is not the answer as lungs do not excrete urea
D is not the answer as lungs do not excrete urea

(a)(ii) An explanation that makes reference to three of the following points:

volume increases / inhalation occurs / air drawn in (1)
diaphragm / intercostal muscles contract (1)
diaphragm moves down / flattens (1)
ribcage expands (1)
pressure decreases (inside thorax / lungs) (1)

Accept: internal intercostal muscles relax; ribs move up / move out; thorax / chest expands; pressure higher outside

(b) An explanation that makes reference to three of the following points:

glucose in urine (1)
glucose released by ultrafiltration (into filtrate) (1)
glucose not reabsorbed / too much glucose (in filtrate) to reabsorb (1)
in the proximal convoluted tubule / PCT / first convoluted tubule (1)
by active transport (1)

Accept: glucose not absorbed into blood; some glucose not reabsorbed
Reject: if active transport pumping glucose into filtrate

Question 3

The diagram shows a human eye with some structures labelled.

(a) Which structure is the retina?

A) P
B) Q
C) R
D) S

(b) A teacher investigates the effect of light intensity on pupil diameter.

This is the teacher’s method:

cover a student’s eyes with a mask
set the light intensity in the room to a low level
remove the mask and wait 20 seconds
record an image of the student’s pupil and iris with a camera
measure the diameter of the pupil on the image using a ruler
repeat two more times at the same light intensity

The teacher repeats the experiment at different light intensities.

The table shows the teacher’s results:

(b)(i) Calculate the mean pupil diameter for the light intensity of 1 arbitrary unit. Give your answer to two significant figures.
(ii) With reference to data in the table, describe the effect of increasing light intensity on the diameter of the pupil.
(iii) Explain the effect of increasing light intensity on the diameter of the pupil.
(iv) State one variable that the teacher should control.
(v) Explain how the teacher’s method ensures that the measurement of the pupil diameters are accurate.

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 3(j): Co-ordination and response — parts (a), (b)(ii), (b)(iii)
• 2(b): Cell structure — part (a)
• 4: Assessment information: Experimental skills — parts (b)(i), (b)(iv), (b)(v)
• Appendix 3: Mathematical skills — part (b)(i)

▶️ Answer/Explanation

Solution

(a) A (P)
B is not the answer as Q is the cornea
C is not the answer as R is the iris
D is not the answer as S is the conjunctiva

(b)(i) 8.2 (2)
Only one mark for: 24.7 OR division by 3 OR 8.23…

(b)(ii) A description that makes reference to two of the following points:
• (diameter) decreases / pupil smaller / eq (1)
• small decrease between 4(au) and 5(au) / starts to level off after 3(au) / starts to level off from 4(au) / large decrease between 2 and 3 (au) / calculated fall / eq (1)

(b)(iii) An explanation that makes reference to three of the following points:
• less light enters (eye) / passes through pupil / eq (1)
• to prevent damage to retina / eq (1)
• (as pupil narrows) circular muscles (of iris) contract (1)
• (as pupil narrows) radial muscles (of iris) relax (1)

(b)(iv) An explanation that makes reference to one of the following points:
• distance from camera (1)
• same student / person / same eye / left or right eye (1)
• food / drinks / caffeine consumed / eq (1)
• recovery time / time spent with mask on (1)
• noise in room (1)
• other light sources / distance from light (1)
• (type of) mask (1)
• colour of light / wavelength of light (1)

(b)(v) An explanation that makes reference to two of the following points:
1. using a camera (to record) / takes a photograph / uses an image / eq (1)
2. waiting 20 s (each time) / waiting same time / eq (1)
3. pupil is not changing size / is stationary / eye has adjusted / eq (1)

Question 4

The photograph shows Prometea, the first cloned horse.

Prometea was produced by cloning, using the nucleus of a skin cell from a horse called Stella Cometa.

(a) Complete the passage about cloning by writing a suitable word or words in each blank space.

A ______ nucleus was taken from a skin cell from Stella Cometa.

This nucleus was inserted into an enucleated ______ that had been taken from a donor horse. An ______ was used to start the type of cell division called ______, eventually producing an embryo. The embryo was then placed into the ______ of the mother.

(b) Until recently, most cloning has been attempted with farm animals.

The table shows some information about the success rates of cloning different farm animals during a four-year period.

Animal	Number in four-year period
	embryos made	live births	surviving at least two years
cattle	7500	75	55
sheep	3500	50	15
goat	500	25	5

Some people now want to use cloning to replace their pets. The cost of cloning a pet cat can be as much as 50 000 United States dollars.

Comment on the use of cloning to replace pets.

Use the information in the table and your own knowledge about variation to support your answer.

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 6(d): Cloning — part (a)
• 6(d): Cloning — part (b)
• 4(b): Inheritance — part (b) – variation aspects

▶️ Answer/Explanation

Solution

(a)

A diploid nucleus was taken from a skin cell from Stella Cometa.

This nucleus was inserted into an enucleated egg (cell) / ovum that had been taken from a donor horse. An (electric) shock / shock was used to start the type of cell division called mitosis, eventually producing an embryo. The embryo was then placed into the uterus / womb of the mother.

(b)

An answer that makes reference to five of the following points:

most embryos made with cattle / fewest embryos made with goats / eq (1)
low success rate / few live births / few survive / pets usually live longer than two years / low life expectancy / eq (1)
cattle have highest survival rate (from live births) / goats have lowest survival rates (from live births) / eq (1)
goats have highest live birth rate / cattle have lowest live birth rate (1)
credit manipulated data (1)
cloning is expensive / not cost effective / more cost than buying a new pet / eq (1)
cloned pets are genetically identical / little genetic variation / could pass on harmful alleles / eq (1)
some variation is environmental / not all variation is genetic / some features of pets will not be same / eq (1)
no data for pets / pets may be different to farm animals / needs to be repeated for pets / eq (1)
raises ethical issues / may not be ethical / eq (1)
pet cloning could provide emotional benefits for people / eq (1)

Question 5

The diagram shows a cross section through a plant leaf.

(a) Which area of the leaf contains xylem vessels?

A) W
B) X
C) Y
D) Z

(b) A student uses this apparatus to measure the water uptake by a cut plant shoot.

(i) The inside of the capillary tube is a cylinder shape. The air bubble moves a length, \( l \), of 5.2 cm in 5 minutes. The inside of the capillary tube has a radius, \( r \), of 0.50 mm. Calculate the rate of water uptake, in \( \text{mm}^3 \) per minute, by the cut plant shoot.

[volume of cylinder = \( \pi r^2 l \)]
[\( \pi = 3.14 \)]

(ii) Describe how the student can use the apparatus to investigate the effect of changing wind speed on water uptake by the cut plant shoot.

(c) A scientist investigates how ABA, an auxin-like substance, affects plant growth. The scientist does not water a plant for 4 days. They then water the plant on day 5.
Graph 1 shows the changes in the ABA concentration in the leaves of the plant.

Graph 2 shows the changes in percentage relative water loss from the leaves of the plant.

Comment on the changes in ABA concentration and water loss in the scientist’s investigation. Use information from both graphs in your answer.

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 3(h): Transport — parts (a), (b)(i), (b)(ii)
• 3(j): Co-ordination and response — part (c)
• 2(b): Cell structure — part (a)
• Appendix 3: Mathematical skills — part (b)(i)

▶️ Answer/Explanation

Solution

(a) C (Y)
A is not the answer as W does not contain xylem
B is not the answer as X does not contain xylem
D is not the answer as Z does not contain xylem

(b)(i) • 8.16(4) (2)
One mark for:
÷ by 5
OR
× 52
OR
× 0.25
OR
0.8(164)
OR
40.82 (allow between 40.82 and 40.85)

Working:
Convert length to mm: \( l = 5.2 \text{ cm} = 52 \text{ mm} \)
Volume = \( \pi r^2 l = 3.14 \times (0.50)^2 \times 52 = 3.14 \times 0.25 \times 52 = 40.82 \text{ mm}^3 \)
Rate = \( 40.82 \div 5 = 8.164 \text{ mm}^3/\text{min} \)

(b)(ii) A description that makes reference to four of the following points:
1. set up potometer underwater / cut stem underwater / dry leaves / eq (1)
2. use a fan at different distances / with and without fans / different fan speeds / eq (1)
3. leave for set time / stated time (1)
4. measure distance bubble moves / distance water moves (on scale) / eq (1)
5. keep other factors constant (1)
6. repeat / reset bubble with reservoir / eq (1)

(c) An answer that makes reference to four of the following points:
1. at start / for first two days, ABA is low / is 0.5 OR at start / for first two days water loss is high / is 100 (1)
2. after two days / from three days ABA increases OR after two days / from three days percentage water loss decreases / eq (1)
3. after five days / after watering / ABA decreases OR after five days / after watering water loss increases / eq (1)
4. as ABA increases water loss decreases / inverse relationship / negative correlation / eq (1)
5. ABA closes stomata / stomata open when ABA low / eq (1)
6. stomata close from two days / stomata close from three days / eq (1)
7. stomata closing reduces transpiration / water loss / evaporation / stomata closing prevents wilting / stomata closing prevents loss of turgidity / ABA reduces transpiration / eq (1)
8. light intensity may change / humidity may change / wind may change / eq (1)

Question 6

Apples contain an enzyme called phenol oxidase.

When apple tissue is exposed to oxygen in the air, this enzyme turns the apple tissue brown.

(a) A student uses this method to investigate the effect of pH on the time taken for apple tissue to turn brown.

mash an apple to produce a pulp
place 25 g of this pulp into a beaker
mix a pH 7 buffer with the pulp to maintain the pH
check the colour of the pulp every five minutes
record the time when the pulp turns brown

The student repeats this method using pH buffers of 3, 5, 9, and 11.

The graph shows the student’s results.

(i) Calculate the percentage increase in time taken for the apple pulp to turn brown at pH 11 compared with the time taken at pH 7.
(ii) Explain why the change in pH affects the time taken for the apple pulp to turn brown.
(iii) Explain how the student could modify this method to give a more accurate measure of the time taken for the apple pulp to turn brown.

(b) A genetically modified (GM) variety of apple has been produced that does not turn brown when exposed to air.

These apples have a gene in their DNA that produces a section of mRNA with a complementary sequence to the mRNA for the phenol oxidase gene.

(i) State two differences between DNA and mRNA.
(ii) Explain why these GM apples do not turn brown when the apple tissue is exposed to air. Use your knowledge of protein synthesis to support your answer.

Most-appropriate topic codes (Edexcel IGCSE Biology):

• 2(c): Biological molecules — parts (a)(ii), (b)(ii)
• 2(c): Enzymes as biological catalysts — parts (a)(ii), (a)(iii)
• 4(b): Inheritance — parts (b)(i), (b)(ii)
• 6(c): Genetic modification (genetic engineering) — part (b)(ii)
• Appendix 3: Mathematical skills — part (a)(i)

▶️ Answer/Explanation

Solution

(a)(i)

• 1400 (%) (2)

One mark for 75 ÷ 5 = 15 OR 70 ÷ 5 = 14

Calculation: Time at pH 11 = 75 minutes, Time at pH 7 = 5 minutes

Percentage increase = \(\frac{75 – 5}{5} \times 100 = \frac{70}{5} \times 100 = 14 \times 100 = 1400\%\)

(a)(ii)

An explanation that makes reference to three of the following points:

1. optimum pH is 7 (1)

2. (pH causes) enzyme to denature (1)

3. shape of enzyme changes / shape of active site changes (1)

4. substrate does not fit active site / enzyme no longer complementary / cannot form enzyme-substrate complexes (1)

(a)(iii)

An explanation that makes reference to two of the following points:

1. use a colour matching chart / light sensor / colorimeter (1)

2. (because) colour change is subjective / to standardise the end colour / so colour is always same (1)

3. use intervals of shorter than 5 minutes / shorter intervals / check more often / check colour constantly (1)

(b)(i)

An answer that makes reference to two of the following points:

1. DNA is double stranded / RNA is single stranded (1)

2. DNA has T (thymine) / RNA has U (uracil) (1)

3. DNA is a helix / RNA is not a helix (1)

4. DNA has deoxyribose / RNA has ribose (1)

(b)(ii)

An explanation that makes reference to four of the following points:

1. (complementary) RNA binds to the phenol oxidase RNA (1)

2. translation cannot occur (1)

3. so enzyme / phenol oxidase not made (1)

AND

Maximum three from:

4. transcription makes mRNA (1)

5. RNA leaves nucleus and enters cytoplasm / RNA moves to ribosome (1)

6. tRNA brings / carries / transports amino acids (1)

7. (during translation) tRNA binds mRNA / anticodons bind codons (1)

8. amino acids join / amino acid chain / makes polypeptide / peptide bonds form (1)

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