IGCSE Biology 0610/33 May/June 2025 Past Paper with Answers

Question 1

A bacterium has a thin layer lying just inside its cell wall, a small separate circular loop of DNA in its cytoplasm, and many tiny dot-like structures scattered through its cytoplasm. Which option correctly matches the cell membrane, the plasmid and the ribosome to these features?

1. the cell membrane is the thin layer just inside the cell wall, the plasmid is the small circular loop of DNA, and the ribosome is one of the tiny dot-like structures
2. the cell membrane is the small circular loop of DNA, the plasmid is the thin layer just inside the cell wall, and the ribosome is one of the tiny dot-like structures
3. the cell membrane is one of the tiny dot-like structures, the plasmid is the thin layer just inside the cell wall, and the ribosome is the small circular loop of DNA
4. the cell membrane is the small circular loop of DNA, the plasmid is one of the tiny dot-like structures, and the ribosome is the thin layer just inside the cell wall

Question 2

Bacteria are living organisms and carry out the seven characteristics of life. Which pair of processes are both characteristics of living organisms shown by bacteria?

1. respiration and reproduction
2. respiration and evaporation
3. condensation and reproduction
4. dissolving and freezing

Question 3

In one country the number of people infected with gonorrhoea per 100 000 people was recorded each year from 2010 to 2020. The number rose from a low value in 2010 to its highest value of 205 per 100 000 people in 2020, and the steepest two-year rise happened between 2014 and 2016. Which option correctly completes the description: overall the number infected ___; the two-year period with the largest change was from ___; and in 2020 the number infected was ___ per 100 000 people?

1. increased; 2014 to 2016; 205
2. decreased; 2010 to 2012; 205
3. increased; 2018 to 2020; 50
4. stayed the same; 2014 to 2016; 100

Question 4 · Answer A

Step 1: A population of 800 000 contains 800 000 ÷ 100 000 = 8 groups of 100 000 people. Step 2: Each group of 100 000 has 100 infected people. Step 3: So the number infected is 100 × 8 = 800 people.

Question 5 · Answer A

Step 1: A mutation can make some bacteria resistant, so the antibiotic no longer kills them. Step 2: These resistant bacteria survive and reproduce, so the resistant type becomes more common each year. Step 3: As more bacteria become resistant, fewer are killed by the antibiotic.

Question 6 · Answer A

Step 1: Barrier methods such as condoms stop the pathogen passing between people during sex. Step 2: Testing identifies infected people so they can be treated, and treatment removes the source of infection. Step 3: Contact tracing finds and treats other people who may be infected, so all three methods in the correct option help control the spread.

Question 7 · Answer A

Step 1: The xylem is the central star-shaped tissue, which is region A. Step 2: Dissolved food such as amino acids is transported in the phloem, which lies between the arms of the xylem, so that is region B. Step 3: So amino acids are transported by B and the xylem is A.

Question 8 · Answer A

Step 1: The wide band of rounded packing cells between the surface of a root and its central tissues is the cortex. Step 2: So the cells of region D are cortex cells. Step 3: Palisade and guard cells are found in leaves and red blood cells are found in animals, so none of these is correct.

Question 9 · Answer A

Step 1: Xylem vessels carry water and dissolved mineral ions up from the roots through the plant. Step 2: The thick walls of xylem also help to support the plant. Step 3: Transporting sugars and amino acids is the job of phloem, and photosynthesis happens in leaf cells, so only the first option gives two functions of xylem.

Question 10 · Answer A

Step 1: A long, thin outgrowth from a surface cell of a root that reaches into the soil is a root hair cell. Step 2: It increases the surface area for absorbing water and mineral ions. Step 3: Guard cells are in leaves, and nerve cells and sperm cells are animal cells, so none of these is correct.

Question 11 · Answer A

Step 1: Osmosis is the movement of water through a partially permeable membrane from a dilute solution to a more concentrated solution. Step 2: Water enters the root hair cell in exactly this way, so the process is osmosis. Step 3: Active transport moves ions using energy, respiration releases energy, and transpiration is water loss from leaves, so none of these describes water entering the root.

Question 12 · Answer A

Step 1: The long, thin shape of a root hair cell gives it a large surface area in contact with the soil. Step 2: A larger surface area allows more water to be absorbed by osmosis. Step 3: A waxy cuticle would reduce uptake, chloroplasts are for photosynthesis, and root cells have no nerve endings, so the key feature is the large surface area.

Question 13 · Answer A

Step 1: Active transport moves substances across a cell membrane against the concentration gradient, so it needs a membrane and energy from respiration. Step 2: Diffusion is the net movement of a substance from a higher to a lower concentration, so a substance moves down a concentration gradient. Step 3: Diffusion does not need energy from respiration, so only the first option matches both processes.

Question 14 · Answer A

Step 1: Aerobic respiration releases energy from glucose using oxygen inside the mitochondria. Step 2: So the structures where aerobic respiration occurs are the mitochondria. Step 3: Chloroplasts carry out photosynthesis, ribosomes make proteins, and the vacuole stores cell sap, so none of these is correct.

Question 15 · Answer A

Step 1: The gland on top of a kidney is the adrenal gland, which secretes adrenaline, so G is the adrenal gland. Step 2: The gland near the stomach is the pancreas, which secretes insulin, so F is the pancreas. Step 3: The male gland is the testes, which secretes testosterone (H), and the female gland is the ovary, which secretes oestrogen (J).

Question 16 · Answer A

Step 1: A hormone is a chemical substance made by an endocrine gland. Step 2: It is carried around the body dissolved in the blood. Step 3: It then alters the activity of specific target organs, so the first option gives the full meaning of a hormone.

Question 17 · Answer A

Step 1: Hormones are carried slowly in the blood, so they act more slowly than the fast electrical impulses of the nervous system. Step 2: Hormones may be involved in homeostasis, for example controlling blood glucose. Step 3: Hormones are chemicals, not impulses, and their effects usually last longer, not shorter, than nervous effects.

Question 18 · Answer A

Step 1: Adrenaline prepares the body for action (the fight-or-flight response). Step 2: The heart pumps more blood carrying oxygen to the muscles, and faster breathing removes more carbon dioxide. Step 3: The pupils widen to let in more light, so the first option correctly completes all four effects.

Question 19 · Answer A

Step 1: Photosynthesis uses carbon dioxide and water as its raw materials. Step 2: Using light energy, these are converted into glucose and oxygen. Step 3: So the word equation is carbon dioxide + water → glucose + oxygen; the reverse equation describes respiration.

Question 20 · Answer A

Step 1: Photosynthesis needs the green pigment chlorophyll, which is held inside the chloroplasts. Step 2: So photosynthesis takes place in the chloroplasts. Step 3: The nucleus controls the cell, the mitochondrion is for respiration, and the cell wall gives support, so none of these is the site of photosynthesis.

Question 21 · Answer A

Step 1: The green colour of a leaf comes from the pigment chlorophyll. Step 2: The white parts of a variegated leaf have no chlorophyll, which is why they are not green. Step 3: Haemoglobin is in blood, glucose is a sugar, and cellulose makes the cell wall, so the green pigment is chlorophyll.

Question 22 · Answer A

Step 1: The decrease in bubbles is 13 − 3 = 10 bubbles per minute. Step 2: Percentage decrease = (decrease ÷ original) × 100 = (10 ÷ 13) × 100 = 76.9. Step 3: Rounded to a whole number this is 77 %.

Question 23 · Answer A

Step 1: The further the lamp is from the plant, the lower the light intensity reaching it. Step 2: Light is needed for photosynthesis, so less light means a slower rate of photosynthesis. Step 3: The bubbles are the oxygen released by photosynthesis, so a slower rate produces fewer bubbles each minute.

Question 24 · Answer A

Step 1: Egg cells are released from the ovary, the small oval organ at the side, which is K. Step 2: Fertilisation usually happens in the oviduct, the narrow tube, which is P. Step 3: An embryo implants in the lining of the uterus, the wide muscular organ, which is L.

Question 25 · Answer A

Step 1: The wide muscular organ where a baby develops is the uterus, so L is the uterus. Step 2: The canal leading to the outside of the body is the vagina, so M is the vagina. Step 3: The narrow ring of muscle between the uterus and the vagina is the cervix, so N is the cervix.

Question 26 · Answer A

Step 1: An egg cell contains energy stores in its cytoplasm to nourish the early embryo. Step 2: It has a jelly coat that changes after fertilisation to stop more than one sperm entering. Step 3: A tail and many mitochondria are features of a sperm cell, a waxy cuticle is a plant feature, and a biconcave shape is a red blood cell feature, so only the first option describes egg cells.

Question 27 · Answer A

Step 1: Discontinuous variation has a limited number of distinct phenotypes with no intermediates, so that statement is correct. Step 2: Variation may be produced by mutation, which is also correct. Step 3: Variation is the differences between individuals, not the similarities between different species, and it is caused by both genes and the environment, not genes only.

Question 28 · Answer A

Step 1: After choosing the most drought-tolerant parents, the farmer breeds these chosen plants together. Step 2: From their offspring, the farmer again chooses those with the highest drought tolerance. Step 3: Repeating this selection and breeding over many generations gradually produces plants that tolerate drought well.

Question 29 · Answer A

Step 1: When humans choose which organisms breed together to improve a feature, the process is selective breeding. Step 2: The farmer is choosing the most drought-tolerant plants to breed, so this is selective breeding. Step 3: Natural selection is driven by the environment, genetic engineering changes genes directly, and cloning makes identical copies, so none of these matches.

Question 30 · Answer A

Step 1: In a binomial name the first word is the genus and the second word is the species. Step 2: In Vicia faba, the first word is Vicia, so Vicia is the genus. Step 3: "faba" is the species, "Vicia faba" is the whole name, and "bean" is a common name, so only Vicia is the genus.

Question 31 · Answer A

Step 1: A yellow-spotted plant must be bb, so all its gametes carry b. Step 2: Crossing Bb with bb gives offspring Bb, bb, Bb, bb. Step 3: Bb plants have black spots and bb plants have yellow spots, so the phenotypic ratio is 1 black-spotted : 1 yellow-spotted.

Question 32 · Answer A

Step 1: There is only one giant water lily but many beetles, so the pyramid of numbers has a very narrow base and a wide bar above it, which is pyramid B. Step 2: The single giant water lily has a very large mass, so the pyramid of biomass has a very wide base that narrows upwards, which is pyramid D. Step 3: So the pyramid of numbers is B and the pyramid of biomass is D.

Question 33 · Answer A

Step 1: An organism receives energy from the chambo fish if it eats the chambo fish. Step 2: The chambo fish are eaten by the kampango catfish and the fish eagles, so the fish eagles receive energy from them. Step 3: Reed grasses, snails and cichlid fish are all lower in the web and are eaten before the chambo fish, so they do not receive energy from it.

Question 34 · Answer A

Step 1: A trophic level is a feeding stage in the web. Step 2: Counting up the longest chain gives reed grasses (1), snails or beetles (2), cichlid fish (3), chambo fish (4), and kampango catfish or fish eagles (5). Step 3: So there are five trophic levels.

Question 35 · Answer A

Step 1: The second trophic level is the primary consumers that eat the producer, which are the snails and beetles, so the snail fits. Step 2: An organism feeding at more than one trophic level eats prey from different levels; the fish eagle eats both chambo fish and kampango catfish. Step 3: So the snail is at the second trophic level and the fish eagle feeds at more than one level.

Question 36 · Answer A

Step 1: Overfishing removes chambo fish faster than they can reproduce, lowering the population. Step 2: A fall in the number of cichlid fish reduces the food available to the chambo fish, so fewer survive. Step 3: Fewer predators, more food, less pollution and a fishing ban would all tend to increase the population, not decrease it.

Question 37 · Answer A

Step 1: Protecting habitats keeps the places where endangered species live, so they can survive and breed. Step 2: Captive breeding programmes increase the numbers of a species in safe conditions. Step 3: Seed banks and zoos store species so they can be bred again in future, so all three methods in the correct option conserve species.

Question 38 · Answer A

Step 1: A sustainable resource is replaced at the same rate as it is used. Step 2: Because it is produced as fast as it is removed, the supply does not run out. Step 3: Using a resource up quickly, never using it, or removing it faster than it is replaced are all the opposite of being sustainable.