IGCSE Biology 0610/41 May/June 2025 Past Paper with Answers

Question 1

In a food chain, the organisms in trophic level 1 are the producers. From where do the organisms in trophic level 1 obtain the energy they use to make their food?

1. from sunlight
2. from eating animals in trophic level 2
3. from minerals taken up by their roots
4. from the heat released by decomposers

Question 2

In a pyramid of energy for an ecosystem, trophic level 1 contains 11 212 J, trophic level 2 contains 9804 J, trophic level 3 contains 822 J and trophic level 4 contains 98 J. Calculate the percentage of energy transferred between trophic levels 2 and 3, giving your answer to one significant figure.

1. 8%
2. 12%
3. 88%
4. 0.8%

Question 3

In a pyramid of energy the amount of energy decreases from one trophic level to the next as you move up the food chain. Which pair of statements both correctly explain why less energy is available at each higher trophic level?

1. energy is lost as heat during respiration, and not all of an organism is eaten or digested
2. energy is created by predators, and all of the energy in food is passed on to the next level
3. energy is lost as light during photosynthesis, and producers use no energy themselves
4. energy is destroyed by decomposers, and every organism in a level is always eaten

Question 4 · Answer A

Step 1: A pyramid of energy shows the energy passing through each level over a period of time, so it represents energy transfer and loss more accurately than a single mass measurement. Step 2: Because it uses energy, it also takes account of differences in life span, reproduction rate and body size, allowing fairer comparisons between ecosystems. Step 3: The other options describe biomass measurements or untrue statements, so they are not advantages of a pyramid of energy.

Question 5 · Answer A

Step 1: A population is all the organisms of one species living together in the same place. Step 2: They must also be living there during the same period, so the two words are area and time. Step 3: Cell, speed and depth do not describe where and when a population lives.

Question 6 · Answer A

Step 1: At first there are plenty of resources and little competition or predation, so the birth rate is greater than the death rate and the population grows. Step 2: As the population gets larger, resources become limited and competition, predation and disease increase, so the death rate rises and the growth rate slows. Step 3: Eventually the birth rate and death rate become equal, so the population levels off and stays roughly constant at X.

Question 7 · Answer A

Step 1: Across the whole retina there are many more rods than cones. Step 2: Cones are concentrated at the fovea, where they reach their highest number, while rods are absent at the fovea itself. Step 3: Rods reach high numbers on either side of the fovea and then fall towards the edges, so the correct option matches both patterns.

Question 8 · Answer A

Step 1: Rod cells respond to low light intensities and give black-and-white vision, while cones need bright light and give colour vision. Step 2: A nocturnal animal must see in dim light, so it benefits from having more rods. Step 3: So a nocturnal retina has more rods because rods are sensitive in dim light, making the correct option the only one that matches both the difference and the reason.

Question 9 · Answer A

Step 1: When light intensity changes, the iris muscles automatically change the size of the pupil. Step 2: This automatic, protective response is called the pupil reflex. Step 3: The knee-jerk reflex involves a leg muscle, phototropism is a plant growth response, and accommodation is focusing on near or far objects.

Question 10 · Answer A

Step 1: In bright light the pupil must get smaller to protect the retina. Step 2: The circular muscles of the iris contract to narrow the pupil, while the radial muscles relax. Step 3: The ciliary muscle changes the lens shape, and there is no suspensory muscle (the suspensory ligaments hold the lens), so the circular muscle is the effector that contracts.

Question 11 · Answer A

Step 1: When the circular muscles contract, the radial muscles relax, producing opposite effects on the pupil. Step 2: A pair of muscles that work against each other in this way are described as antagonistic. Step 3: Synergistic muscles work together, voluntary actions are under conscious control, and rhythmic refers to a regular repeating action, so antagonistic is correct.

Question 12 · Answer A

Step 1: The small round sacs inside the end of the first neurone are vesicles, which store the neurotransmitter. Step 2: The tiny particles released into and crossing the synaptic gap are the neurotransmitter molecules. Step 3: The structure on the membrane of the second neurone that the neurotransmitter binds to is the receptor, so the correct option names all three correctly.

Question 13 · Answer A

Step 1: The neurotransmitter is released on the first neurone side, so it is at a high concentration there and a low concentration on the far side. Step 2: Particles move from a high to a low concentration by diffusion, so the neurotransmitter diffuses across the gap. Step 3: It does not need energy (so not active transport), it is not water movement (so not osmosis), and an electrical impulse cannot cross the gap directly.

Question 14 · Answer A

Step 1: After pollination the pollen grain grows a tube down through the style towards the ovule. Step 2: This structure is called the pollen tube and it carries the male nucleus to the ovule. Step 3: The oviduct is in animals, the xylem carries water, and the anther produces pollen, so none of these is the growing tube.

Question 15 · Answer A

Step 1: The pollen tube grows down through the style until it reaches the ovule in the ovary. Step 2: The male nucleus from the pollen grain travels down the inside of the pollen tube. Step 3: The male nucleus then fuses with the female nucleus inside the ovule, and this fusion of nuclei is fertilisation.

Question 16 · Answer A

Step 1: Self-pollination does not depend on another plant or on a pollinator, so it works even when pollinators are scarce or the plant is isolated. Step 2: Because pollen only has to reach the same flower, less pollen and energy are wasted and the chance of successful pollination is higher. Step 3: Self-pollination reduces genetic variation rather than increasing it, and it does not make all offspring male, so the other options are wrong.

Question 17 · Answer A

Step 1: Self-pollination uses gametes from the same plant, so it produces offspring with very little genetic variation. Step 2: With little variation, fewer individuals are likely to have alleles that help them survive a new disease or a change in conditions. Step 3: This makes the population less able to adapt and more vulnerable to disease, so its risk of extinction rises.

Question 18 · Answer A

Step 1: A mutation is a random change in a gene or chromosome that can create a new allele, which is a source of variation. Step 2: Random fertilisation means any male gamete can fuse with any female gamete, producing new combinations of alleles. Step 3: Respiration, digestion, diffusion, osmosis, transpiration and translocation are not sources of genetic variation, so only mutation and random fertilisation are correct.

Question 19 · Answer A

Step 1: Mitosis is the division of a nucleus that produces two genetically identical cells, each with the same chromosome number as the parent cell. Step 2: This happens because the chromosomes are copied and the copies separate into the two new cells. Step 3: Its roles are growth, the repair and replacement of damaged cells, and asexual reproduction, so the first option is correct while the others describe meiosis, respiration or fertilisation.

Question 20 · Answer A

Step 1: Unspecialised cells that divide repeatedly by mitosis and can develop into different specialised cell types are called stem cells. Step 2: Red blood cells and nerve cells are already specialised and do not divide. Step 3: Gametes are specialised sex cells made by meiosis, so the correct answer is stem cells.

Question 21 · Answer A

Step 1: Excretion is the removal of substances the body makes during its chemical reactions (metabolism) that it does not need. Step 2: It also includes getting rid of useful substances when they are present in excess of what the body requires. Step 3: Removing undigested food is egestion, taking in oxygen and glucose is absorption, and breaking down food is digestion, so only the first option defines excretion.

Question 22 · Answer A

Step 1: Respiration in cells produces carbon dioxide as a waste product, which is carried in the blood to the lungs. Step 2: The carbon dioxide diffuses into the alveoli and is breathed out, so it is excreted by the lungs. Step 3: Urea is excreted by the kidneys, while glucose and amino acids are useful substances that are not normally excreted.

Question 23 · Answer A

Step 1: The cortex is the outer band of kidney tissue lying just beneath the surface. Step 2: The medulla is the inner region of tissue deeper inside the kidney. Step 3: The ureter is the tube that carries urine away from the kidney to the bladder, so the first option names all three correctly.

Question 24 · Answer A

Step 1: X contains blood, including large proteins and blood cells, because no filtration has happened yet. Step 2: Between X and Y filtration removes small molecules, so Y contains glucose, water, urea and ions but no proteins or cells, which are too big to be filtered. Step 3: As the fluid flows to Z, all the glucose and much of the water and ions are reabsorbed into the blood, so Z contains urine with no glucose and a higher concentration of urea.

Question 25 · Answer A

Step 1: Excess amino acids cannot be stored, so the liver removes their nitrogen-containing part in a process called deamination, forming urea. Step 2: The liver also builds amino acids up into proteins, which is part of assimilation. Step 3: The nitrogen is not breathed out as carbon dioxide, amino acids do not form starch, and this processing happens in the liver, not the kidneys, so the other options are wrong.

Question 26 · Answer A

Step 1: Apes and rodents are mammals, so the feature appearing where their line begins, at A, would be a mammal feature such as hair or external ears. Step 2: Birds have wings and feathers, so the feature appearing where the bird line separates, at B, would be wings or feathers. Step 3: Gills, scales, roots and a backbone are not the features that distinguish these particular groups here, so the first option is correct.

Question 27 · Answer A

Step 1: The most recent common ancestor is found where two branches separate highest up the tree, meaning least time has passed since they split. Step 2: The apes and rodents branches separate higher than any other pair, so they share the most recent common ancestor. Step 3: Sharks, bony fish, crocodiles and birds split off lower down, so their common ancestors are older.

Question 28 · Answer A

Step 1: The more recently two groups shared a common ancestor, the more similar their DNA base sequences are. Step 2: Birds share the most recent common ancestor with crocodiles, so birds have the most similar DNA to crocodiles. Step 3: Sharks branched off earliest, so they are the most distantly related and have the least similar DNA to crocodiles.

Question 29 · Answer A

Step 1: DNA is made of two strands that twist around each other to form a double helix. Step 2: It contains four bases, A, T, C and G, and these pair in a fixed way, with A always pairing with T and C always pairing with G. Step 3: The paired bases are held together by bonds, so the first option is correct; the others describe a sugar, a protein, or impossible pairing.

Question 30 · Answer A

Step 1: The order of bases in a gene determines the order in which amino acids are joined together. Step 2: The amino acids join to form a protein, such as an enzyme, and the order of amino acids gives the protein its particular shape. Step 3: Because proteins like enzymes control the cell’s reactions, the base sequence controls cell function, so only the first option is correct.

Question 31 · Answer A

Step 1: Auxin is made in the tips of the shoot and root and travels away from the tip by diffusion. Step 2: Because the clinostat rotates, the effect of gravity is spread equally on all sides of the root, so the auxin becomes equally distributed. Step 3: Auxin stimulates cell elongation, and with auxin spread evenly the root grows out straight rather than bending, so the first option fills every gap correctly.

Question 32 · Answer A

Step 1: When the board stops rotating, gravity now acts on one side of each root only. Step 2: Auxin gathers on the lower side, and in roots this slows growth on that side so the root bends downwards. Step 3: Roots are positively geotropic, so they grow downwards in the direction of gravity once the clinostat stops.

Question 33 · Answer A

Step 1: A tropism is named after the stimulus that causes the growth response. Step 2: The stimulus here is light, and the prefix for light is photo, so the response is phototropism. Step 3: Geotropism is a response to gravity, hydrotropism to water, and thermotropism to temperature, so phototropism is the response to light.

Question 34 · Answer A

Step 1: A wilted plant has lost water, so water leaves the cells by osmosis. Step 2: As water leaves, the vacuole and cytoplasm shrink, the cells lose turgor pressure and become flaccid. Step 3: If a lot of water is lost, the cell membrane pulls away from the cell wall, which is plasmolysis, so the first option correctly states and explains the appearance.