IGCSE Biology 0610/21 May/June 2025 Past Paper with Answers

Question 1

Which characteristic of living organisms requires carbon dioxide to diffuse into a leaf?

1. nutrition
2. excretion
3. movement
4. respiration

Question 2

Which set of features is characteristic only of birds?

1. hard-shelled eggs and feathers
2. hair and wings
3. scales and soft-shelled eggs
4. wings and soft-shelled eggs

Question 3

Which structures are found in both plant cells and animal cells?

1. cell membranes and nuclei
2. cell walls and cell membranes
3. nuclei and cell walls
4. cytoplasm and chloroplasts

Question 4 · Answer A

Step 1: Active transport moves particles from a low to a high concentration, so statement 1 is correct and statement 2 is wrong. Step 2: It needs energy from respiration, so statement 3 is correct, and because it needs respiration it can only happen in living cells, so statement 4 is correct. Step 3: Therefore statements 1, 3 and 4 are correct.

Question 5 · Answer A

Step 1: In DNA the bases pair in a fixed way: adenine pairs with thymine, and cytosine pairs with guanine. Step 2: So thymine and adenine form a correct base pair. Step 3: The other combinations mix bases that do not pair together.

Question 6 · Answer A

Step 1: Protein is detected with the biuret test, which does not need heating. Step 2: A positive biuret test changes the colour from blue to purple. Step 3: The Benedict’s test is for reducing sugars, needs heating and gives a brick-red colour, so it is not the protein test.

Question 7 · Answer A

Step 1: Above its optimum temperature an enzyme is denatured, which changes the shape of its active site. Step 2: With a changed active site the substrate no longer fits, so fewer reactions occur and activity falls. Step 3: Enzymes are not alive so cannot be killed, they are not used up, and faster-moving reactants would increase activity, not lower it.

Question 8 · Answer A

Step 1: Spongy mesophyll has many air spaces that allow efficient gas exchange. Step 2: The long, rectangular cells packed with chloroplasts to absorb light are the palisade mesophyll, not the spongy mesophyll. Step 3: So spongy mesophyll has air spaces but not long rectangular light-absorbing cells.

Question 9 · Answer A

Step 1: The child eats more vitamin C (54 mg) than the RDA (50 mg) and exactly the RDA of iron (11 mg), so scurvy and anaemia are not risks. Step 2: The child eats only 5 units of vitamin D against an RDA of 10, so vitamin D is short, which causes rickets. Step 3: Therefore only condition 2, rickets, is a risk.

Question 10 · Answer A

Step 1: Assimilation is the taking in and use of absorbed nutrients by the cells of the body. Step 2: So the uptake and use of nutrients by cells is assimilation. Step 3: Absorption is the movement of nutrients into the blood, ingestion is taking food into the body, and egestion is removing undigested waste.

Question 11 · Answer A

Step 1: Trypsin is a protease, so it breaks down protein. Step 2: Trypsin is made in the pancreas and works in the small intestine, so it breaks down protein in the small intestine. Step 3: Maltose is broken down by maltase, and the protease in the stomach is pepsin, not trypsin.

Question 12 · Answer A

Step 1: The lacteal is a lymph vessel that absorbs the products of fat digestion. Step 2: It runs up the centre of each villus, so the central vessel is the lacteal. Step 3: The outer layer is the epithelium where absorption occurs, and the surrounding capillaries carry away glucose and amino acids.

Question 13 · Answer A

Step 1: Transpiration depends on water vapour diffusing out of the leaf into the air. Step 2: Higher humidity means more water vapour already in the air, so the concentration gradient is smaller and transpiration falls. Step 3: So as humidity increases the rate of transpiration falls steadily.

Question 14 · Answer A

Step 1: A source makes or releases sugars, and a sink uses or stores them. Step 2: In spring the green leaves photosynthesise and export sugars, so they are sources. Step 3: The growing flowers use up sugars, so they are sinks.

Question 15 · Answer A

Step 1: In a single circulation the blood passes through the heart only once per circuit. Step 2: Blood leaving the heart goes first to the gills to be oxygenated, then on to the body, including the muscles. Step 3: From the muscles it returns straight to the heart, so the order is gills, muscles, heart.

Question 16 · Answer A

Step 1: The structures detected on a pathogen are its antigens, so W is antigens. Step 2: Antibodies are made to destroy pathogens directly, so X is antibodies, and the cells that engulf marked pathogens are phagocytes, so Y is phagocytes. Step 3: The cells kept for long-term immunity are memory cells, so Z is memory cells.

Question 17 · Answer A

Step 1: The cholera toxin acts on the wall of the gut. Step 2: It causes water to move out of the blood and into the gut. Step 3: This extra water in the gut produces severe watery diarrhoea, which can cause dehydration.

Question 18 · Answer A

Step 1: A decreasing lung volume means the person is breathing out. Step 2: Quiet expiration is passive: the diaphragm relaxes and the external intercostal muscles relax, so the ribs fall and the chest volume decreases. Step 3: So at point X the diaphragm and the external intercostal muscles are both relaxing.

Question 19 · Answer A

Step 1: Cell division and muscle contraction both need energy released by respiration. Step 2: Diffusion and osmosis are passive processes that do not require energy from respiration. Step 3: So only processes 1 and 3 require energy from respiration.

Question 20 · Answer A

Step 1: The glomerulus is a knot of capillaries where blood is filtered under pressure. Step 2: Small molecules such as water, glucose, urea and ions are filtered out of the blood into the tubule. Step 3: Reabsorption happens later along the tubule, protein synthesis happens at ribosomes, and deamination happens in the liver.

Question 21 · Answer A

Step 1: The small sac in the ending of neurone 1 that stores the chemical is a vesicle, so P is a vesicle. Step 2: The chemical released into the gap is the neurotransmitter (Q), and the gap itself is the synaptic gap (R). Step 3: The site on neurone 2 that the chemical binds to is the receptor, so S is the receptor.

Question 22 · Answer A

Step 1: Rod cells are very sensitive to dim light, so they are used for night vision. Step 2: Rod cells cannot tell colours apart; colour vision is the job of cone cells. Step 3: So rod cells are used for night vision but not for colour vision.

Question 23 · Answer A

Step 1: The glands on top of the kidneys are the adrenal glands, which release adrenaline. Step 2: Adrenaline prepares the body for action, widening the pupils to let in more light. Step 3: Adrenaline also increases heart rate and blood glucose, so the decreases listed are wrong, and sexual characteristics develop in response to sex hormones.

Question 24 · Answer A

Step 1: When the body overheats, the arterioles supplying the skin capillaries widen, which is vasodilation. Step 2: More blood then flows near the skin surface, so more heat is lost to the surroundings. Step 3: Vasoconstriction would reduce heat loss (a response to cold), and it is the arterioles, not the veins, that control this flow.

Question 25 · Answer A

Step 1: A tropism is a growth response to a stimulus, and phototropism is a response to light. Step 2: A shoot growing towards light is phototropism. Step 3: Growth in response to gravity is gravitropism, and reactions using light such as photosynthesis are not tropisms.

Question 26 · Answer A

Step 1: Antibiotics work on structures and processes found in bacteria, so they kill bacteria. Step 2: Viruses do not have these structures, so antibiotics have no effect on viruses. Step 3: So antibiotics kill bacteria but do not affect viruses.

Question 27 · Answer A

Step 1: Producing offspring from one parent by budding is asexual reproduction. Step 2: Asexual reproduction involves no gametes, so the offspring is genetically identical to the parent. Step 3: So the parent and offspring are genetically identical and this is asexual reproduction.

Question 28 · Answer A

Step 1: A sharp peak at about day 14 is the LH surge that triggers ovulation, so W is LH. Step 2: Oestrogen rises during the first half of the cycle and peaks just before day 14, so the gradually rising curve Y is oestrogen. Step 3: Progesterone rises in the second half of the cycle, so neither curve here is progesterone.

Question 29 · Answer A

Step 1: Mitosis copies every chromosome and shares the copies equally between two daughter cells. Step 2: Each daughter cell therefore has the same number of chromosomes as the parent and an identical set. Step 3: Halving the chromosome number happens in meiosis, and the number is never doubled in the daughter cells.

Question 30 · Answer A

Step 1: The first cross gives a mixture of red and white hair (roan), so neither allele is fully dominant; both are expressed together, which is codominance. Step 2: Crossing two roan (heterozygous) cattle then gives 1 red : 2 roan : 1 white, the ratio expected from codominance. Step 3: If one colour were dominant the offspring would not show the blended roan phenotype.

Question 31 · Answer A

Step 1: All body cells from the same organism contain the same genes, so statement 2 is correct. Step 2: A specialised cell only switches on (expresses) the genes for the proteins it needs, so statement 3 is correct. Step 3: Different specialised cells express different genes, so statement 1 is wrong.

Question 32 · Answer A

Step 1: In a hot, dry habitat a plant must reduce water loss. Step 2: Few stomata, a thick waxy cuticle and a small surface area all reduce the amount of water lost. Step 3: Many stomata, a thin cuticle or a large surface area would all increase water loss, so they are not suited to dry habitats.

Question 33 · Answer A

Step 1: Natural selection happens without human involvement, driven by the environment. Step 2: Wild animals evolving long necks to reach high leaves is natural selection with no humans involved. Step 3: Artificial selection is carried out by humans, antibiotic resistance arises by natural selection, and making insulin is genetic engineering, so the other rows are mismatched.

Question 34 · Answer A

Step 1: A pyramid of energy has a bar for each trophic level whose size shows the energy at that level. Step 2: So it shows the energy stored at each trophic level. Step 3: It does not directly show the energy lost between levels, the input from the Sun, or one total for the whole ecosystem.

Question 35 · Answer A

Step 1: A secondary consumer eats a primary consumer. The sea otter, seal, sea lion and orca whale all eat primary consumers, so there are four secondary consumers. Step 2: A tertiary consumer eats a secondary consumer. Only the orca whale eats the seal and sea lion (which are secondary consumers), so there is one tertiary consumer. Step 3: So there are four secondary consumers and one tertiary consumer.

Question 36 · Answer A

Step 1: Nitrate appeared only in the unheated soil, so something in that soil turned the added ammonium into nitrate. Step 2: Nitrifying bacteria convert ammonium ions into nitrate ions; heating to 100 degrees Celsius killed them in the heated sample, so no nitrate formed. Step 3: All nitrate had already been removed, so it was not broken down, and ammonium was added directly, so nitrogen fixation was not needed.

Question 37 · Answer A

Step 1: The lag phase is the first part of the curve, where the population grows only slowly as organisms adjust and begin to reproduce. Step 2: So the region at the very start, where the population rises slowly, is the lag phase. Step 3: The steeply rising part is the exponential (log) phase, and the flat top is the stationary phase.

Question 38 · Answer A

Step 1: Biodiversity is the number of different species found in an area. Step 2: So the term for the number of different species living in an area is biodiversity. Step 3: Conservation is protecting species, an ecosystem is a community plus its environment, and a population is all the members of one species.

Question 39 · Answer A

Step 1: Eutrophication is caused by extra nutrients, such as nitrates, entering water. Step 2: Sewage adds these nutrients to water, so it can cause eutrophication. Step 3: Carbon dioxide and methane are greenhouse gases, and non-biodegradable plastic pollutes physically, so none of these cause eutrophication.

Question 40 · Answer A

Step 1: First the plasmid is cut open with restriction enzymes (process 1) so the human gene can be added. Step 2: The recombinant plasmids are then inserted into bacteria (process 3), and those bacteria are allowed to multiply (process 4). Step 3: Finally the bacteria express the human gene to make insulin (process 2), giving the order 1, 3, 4, 2.