Paper 22, worked through. Cambridge IGCSE Biology, May/June 2026: worked solutions

Forty questions, one mark each, 45 minutes: just over a minute a question. A lot of this paper is diagrams and graphs, so read the labels and the axes before the answers. If one is taking too long, put a mark beside it, guess, and come back at the end: a blank scores the same as a wrong answer.

1. 1Deciding which characteristics of living things a person shows by getting up, opening a door and walking.[1]
   Show how to do itHide the working

   1. Go through what happens. He sees the door and opens it: he is responding to his surroundings, which is sensitivity.
   2. Walking needs energy, and that energy is released from food in his cells by respiration.
   3. Respiration makes carbon dioxide as a waste product, and he breathes it out the whole time. Getting rid of the waste products of metabolism is excretion.
   4. Nothing in a short walk shows growth, nutrition or reproduction. Each of the other choices contains one of those.

   AnswerA: excretion, respiration and sensitivity.

   Respiration is not breathing. It is the chemical reactions in cells that release energy, and it never stops.

   Cross out any choice with a characteristic that takes much longer than a few minutes to show, such as growth.

   Revise this: What living things do
2. 2Using the features of the arthropod groups to count animals on a bar chart.[1]
   Show how to do itHide the working

   1. Insects have three pairs of jointed legs. Arachnids have four pairs, crustaceans have more than four pairs, and myriapods have many.
   2. So "more than three pairs" means every group except the insects.
   3. Read the bars: arachnids 10, crustaceans 12, myriapods 5. 10 + 12 + 5 = 27.

   AnswerA: 27.

   "More than three pairs" leaves the insects out, because they have exactly three. Adding all four bars is the trap.

   Check the scale before reading a bar: each small square here is worth one.

   Revise this: The groups of living things
3. 3Naming the part of the cell where aerobic respiration happens.[1]
   Show how to do itHide the working

   1. Aerobic respiration releases energy from glucose using oxygen. It takes place in the mitochondria.
   2. That is why cells that need a lot of energy, such as muscle cells, have many mitochondria.

   AnswerB: mitochondrion.

   Ribosomes make proteins. The cytoplasm is where anaerobic respiration happens, which is why it is offered.

   Revise this: Cell structure
4. 4Working out the real size of something from its measured image and the magnification.[1]
   Show how to do itHide the working

   1. Actual size = image size ÷ magnification. The 6 mm is the size of the image.
   2. 6 ÷ 40 = 0.15 mm.
   3. The answer is wanted in micrometres. There are 1000 micrometres in a millimetre: 0.15 × 1000 = 150 μm.

   AnswerD: 150 μm.

   Change the units as well as dividing. 0.15 is the right number in millimetres and appears among the choices as micrometres, to catch people who stop early.

   The actual size is always smaller than the image. Multiplying by 40 goes the wrong way.

   Revise this: Magnification
5. 5Reading a ratio from a graph and using it to find a final length.[1]
   Show how to do itHide the working

   1. Find 0.1 on the concentration axis and read the ratio above it: 1.2.
   2. The ratio is final length ÷ initial length, so final length = ratio × initial length.
   3. 1.2 × 4 cm = 4.8 cm.

   AnswerB: 4.8 cm.

   1.2 is the ratio, not the length. It is offered as a length in centimetres for anyone who reads the graph and stops.

   A ratio above 1 means the potato got longer: it took in water by osmosis from the dilute solution.

   Revise this: Osmosis
6. 6Recalling which bases pair up across the two strands of DNA.[1]
   Show how to do itHide the working

   1. The two strands are held together by bonds between pairs of bases, and the pairing is always the same.
   2. A pairs with T, and C pairs with G.

   AnswerD: T and A.

   Learn the pairs as "A with T, C with G". Every wrong row puts a base with the wrong partner.

   Revise this: Chromosomes, genes and DNA
7. 7Choosing the true statement about how enzymes work.[1]
   Show how to do itHide the working

   1. As the temperature rises towards the optimum, molecules move faster, so the enzyme and its substrate collide more often and more of the collisions work. The rate is highest at the optimum.
   2. Above the optimum the molecules have even more kinetic energy, not less, but the enzyme's active site loses its shape, so the substrate no longer fits.
   3. An enzyme fits only its own substrate: maltase fits maltose, not starch. And pepsin, in the stomach, works best in acid.

   AnswerD: effective collisions are most frequent at the optimum temperature.

   Kinetic energy keeps going up as it gets hotter. The rate falls above the optimum because the enzyme is denatured, not because the molecules slow down.

   Revise this: Enzymes
8. 8Comparing rates of reaction from the slopes of lines on a graph.[1]
   Show how to do itHide the working

   1. The rate is the mass of sugar made each second, which is the slope of the straight part of each line.
   2. P makes 20 g in the first 20 s: 20 ÷ 20 = 1.0 g/s.
   3. Q makes about 14.5 g in the first 20 s: about 0.72 g/s.
   4. R makes 30 g in 80 s: 30 ÷ 80 = 0.375 g/s.
   5. S is given as 0.75 g/s. In order: P (1.0), S (0.75), Q (about 0.72), R (about 0.38).

   AnswerB: P, then S, then Q, then R.

   Use the early, straight part of each line. P and Q finish at the same height, 30 g, so the final amount tells you nothing about how fast they got there.

   S and Q are close, so read Q's line carefully against the grid.

   Revise this: Enzymes
9. 9Tracing the route by which a raw material for photosynthesis reaches the chloroplasts.[1]
   Show how to do itHide the working

   1. Carbon dioxide enters a leaf through the stomata, the pores mostly on the underside.
   2. Inside, it diffuses through the air spaces between the spongy mesophyll cells, then into the cells and their chloroplasts.
   3. Water arrives in the xylem, but it goes to the mesophyll cells, not through the epidermis.

   AnswerB: carbon dioxide through the stomata, the air spaces of the spongy mesophyll, then into chloroplasts.

   The cuticle is waxy and waterproof. Almost nothing gets through it, which is its job.

   Phloem carries sugars away from the leaf. It does not bring water in.

   Revise this: Leaf structure
10. 10Naming a layer in a section through a leaf.[1]
    Show how to do itHide the working

    1. Work down from the top. First a thin layer with no chloroplasts: the upper epidermis. Then tall cells packed side by side and full of chloroplasts: the palisade mesophyll.
    2. Layer X is underneath those. Its cells are rounded and loosely packed, with large air spaces between them. That is the spongy mesophyll.
    3. Below X is the lower epidermis, a single layer with guard cells and stomata in it.

    AnswerC: spongy mesophyll.

    Palisade cells are tall and tightly packed. Spongy cells are rounded with gaps. The gaps are what to look for.

    Revise this: Leaf structure
11. 11Deciding which vessel leaving a villus carries the most fatty acids.[1]
    Show how to do itHide the working

    1. A villus has two kinds of vessel. The network of blood capillaries takes up glucose and amino acids. The lacteal, the single vessel up the middle, takes up fatty acids and glycerol.
    2. In the diagram the central vessel joins the thicker vessel underneath. The arrow that leaves along that vessel is carrying what the lacteal absorbed.
    3. The two arrows on the left are flowing in, before anything has been absorbed, so they cannot be the highest.

    AnswerC: the arrow leaving through the lacteal.

    Fats go into the lacteal, not into the blood capillaries. That one fact separates the two arrows on the right.

    Revise this: Absorbing food
12. 12Finding xylem and phloem in a cross-section of a root.[1]
    Show how to do itHide the working

    1. In a root the xylem is in the centre, usually in the shape of a cross or star.
    2. The phloem is in separate small patches between the arms of the xylem.
    3. Look for the diagram where the xylem label reaches the central star and the phloem label reaches one of the small circles.

    AnswerA: phloem is the small circles, xylem is the central star.

    Follow each label line to where it actually ends. In two of the diagrams a line stops at the outer part of the root, and in one the two labels are swapped.

    This is the arrangement in a root. In a stem the bundles are arranged in a ring.

    Revise this: Transport in plants
13. 13Explaining why plants lose water by transpiration.[1]
    Show how to do itHide the working

    1. A leaf needs carbon dioxide for photosynthesis, and it can only get in through open stomata.
    2. While the stomata are open, water vapour in the air spaces of the leaf diffuses out through them, because there is more water vapour inside the leaf than outside.
    3. So transpiration is the unavoidable result of having stomata open for gas exchange.

    AnswerA: the stomata have to be open for carbon dioxide to enter, so water vapour diffuses out.

    Roots take in water by osmosis, not active transport. Xylem carries water and mineral ions, not amino acids. And photosynthesis uses water: it does not make it.

    Revise this: Transpiration
14. 14Choosing the correctly labelled diagram of translocation.[1]
    Show how to do itHide the working

    1. Translocation is the movement of sucrose and amino acids in the phloem. So the sugar being carried must be sucrose, not glucose. Use the key to see which symbol is which.
    2. It moves from a source, where it is made or released, to a sink, where it is used or stored. The arrow starts at the source and ends at the sink.
    3. Only one diagram has sucrose in it and has the arrow running from the cell labelled source to the cell labelled sink.

    AnswerC: sucrose moving from the source to the sink.

    Two things to check, in this order: the right sugar, then the direction of the arrow. Each wrong diagram fails one of them.

    Revise this: Translocation
15. 15Saying what a double circulation is.[1]
    Show how to do itHide the working

    1. In mammals the blood goes from the heart to the lungs and back to the heart, and then from the heart round the body and back again.
    2. So in one complete circuit, the blood passes through the heart twice.

    AnswerC: blood flows through the heart twice for each circulation.

    There is one heart with two sides, not two hearts. A fish has a single circulation: the blood passes through its heart once per circuit.

    Revise this: Circulation and the heart
16. 16Recalling what the pulmonary vein carries and which way.[1]
    Show how to do itHide the working

    1. Veins carry blood towards the heart. Pulmonary means to do with the lungs.
    2. So the pulmonary vein carries blood from the lungs to the heart, and blood that has just been through the lungs is oxygenated.

    AnswerD: oxygenated blood, to the heart.

    This is the one vein that carries oxygenated blood. What makes a vessel a vein is the direction, towards the heart, not what is in it.

    Revise this: Blood vessels
17. 17Recognising the description of passive immunity.[1]
    Show how to do itHide the working

    1. In passive immunity the body does not make its own antibodies. It is given them ready-made, for example across the placenta or in breast milk.
    2. It works straight away but does not last, because no memory cells are made.

    AnswerA: defence by antibodies acquired from another individual.

    If the body makes the antibodies itself, after an infection or a vaccination, that is active immunity. Two of the other statements describe that.

    Revise this: Disease and immunity
18. 18Locating where the cholera toxin acts in the alimentary canal.[1]
    Show how to do itHide the working

    1. The cholera bacterium releases a toxin in the small intestine. It makes the cells lining the small intestine secrete chloride ions into the space inside.
    2. The chloride ions lower the water potential there, so water follows by osmosis out of the blood, which causes the diarrhoea and dehydration.
    3. On the diagram the small intestine is the long coiled tube in the middle.

    AnswerB: the small intestine.

    The large intestine is the wider tube round the outside of the coils, and the stomach is the bag at the top. Trace each label line to its end before choosing.

    Revise this: Disease and immunity
19. 19Matching the two sets of intercostal muscles to parts of a graph of chest volume.[1]
    Show how to do itHide the working

    1. When the volume of the thorax is rising, air is being breathed in. The external intercostal muscles contract and pull the ribs up and out.
    2. When the volume falls far below its normal level, that is a forced breath out. The internal intercostal muscles contract and pull the ribs down and in.
    3. On the graph, Q to R is the big rise in volume, so that is the external muscles. R to S is the big fall, down to 1200 cm³, so that is the internal muscles.

    AnswerC: internal muscles from R to S, external muscles from Q to R.

    External for breathing in, internal for breathing out hard. It is the opposite of what the names seem to suggest, which is why it gets asked.

    Check which column is which before you choose. The right pair of regions also appears with the columns the other way round.

    Revise this: Breathing and gas exchange
20. 20Finding what aerobic and anaerobic respiration have in common.[1]
    Show how to do itHide the working

    1. Both kinds of respiration release energy by breaking down glucose, C₆H₁₂O₆.
    2. Only aerobic respiration uses oxygen. Neither uses carbon dioxide: it is a product. And an oxygen debt comes only from anaerobic respiration in muscles.

    AnswerA: both break down glucose.

    Respiration never uses carbon dioxide. Photosynthesis does.

    Revise this: Aerobic respiration
21. 21Stating the job of a glomerulus.[1]
    Show how to do itHide the working

    1. A glomerulus is the knot of capillaries at the start of each kidney tubule.
    2. Blood arrives under high pressure, and water, glucose, urea and ions are forced out of it into the tubule. Blood cells and large proteins are too big and stay behind. That is filtration.

    AnswerB: filtering the blood.

    Glucose is reabsorbed further along the tubule, not in the glomerulus. Urea is made in the liver, by deamination, and only removed by the kidney.

    Revise this: Excretion and the kidneys
22. 22Finding where a motor neurone receives a signal from another neurone.[1]
    Show how to do itHide the working

    1. At a synapse, the neurone before it releases neurotransmitter molecules. They diffuse across the gap and bind to receptor proteins on the next neurone.
    2. A neurone receives signals at the ends of its dendrites, the short branches around its cell body.
    3. The far end of the long axon is where this neurone releases its own neurotransmitter, on to a muscle. It does not have the receptors there.

    AnswerB: at the ends of the dendrites.

    Releasing and binding happen on opposite sides of a synapse. The question asks where the molecules bind, which is the receiving end.

    Revise this: Nerves and reflexes
23. 23Using a graph of blood glucose to say when glucagon would be highest.[1]
    Show how to do itHide the working

    1. Glucagon is the hormone released when blood glucose is too low. It makes the liver turn stored glycogen back into glucose.
    2. So glucagon is highest when the blood glucose is at its lowest.
    3. On the graph the three tall peaks follow meals. The lowest point of the whole day is the dip at about 15:00.

    AnswerC: 14:00 to 15:30.

    Insulin goes with the peaks, glucagon goes with the dips. The three other time slots all sit on a peak.

    Glucagon, glycogen and glucose are three different things. Glucagon is the hormone.

    Revise this: Homeostasis
24. 24Predicting how a shoot grows when the seedling is turned constantly.[1]
    Show how to do itHide the working

    1. A shoot normally grows upwards, away from gravity, because auxin collects on its lower side and makes that side grow faster.
    2. On a disc that keeps rotating, every side of the shoot spends the same time facing down. The auxin ends up spread evenly.
    3. With no side growing faster than another, the shoot does not bend. It grows straight out in the direction it was already pointing.

    AnswerA: the straight shoot.

    The turning disc cancels out the effect of gravity. Any diagram with a bend in it shows a response to gravity that cannot happen here.

    Revise this: Plant responses
25. 25Recalling what antibiotics work against.[1]
    Show how to do itHide the working

    1. Antibiotics kill bacteria or stop them growing, by damaging structures or processes that bacteria have.
    2. Viruses do not have those structures and reproduce inside the body's own cells, so antibiotics have no effect on them.

    AnswerC: bacteria only.

    Antibiotics do nothing for a cold or flu, because those are caused by viruses.

    Revise this: Drugs and antibiotics
26. 26Describing pollination.[1]
    Show how to do itHide the working

    1. Pollen is made in the anthers, the male part of a flower.
    2. Pollination is the transfer of pollen grains from an anther to a stigma, the top of the female part.

    AnswerC: from an anther to a stigma.

    The filament is only the stalk that holds the anther up. And pollination is not fertilisation: that happens later, in the ovule.

    Revise this: Reproduction in flowering plants
27. 27Choosing the true statement about human reproduction.[1]
    Show how to do itHide the working

    1. The egg cell is large because its cytoplasm holds an energy store, which the embryo uses for its first divisions.
    2. Check the others against the exact wording you have learned. It is an embryo, a ball of cells, that embeds in the lining of the uterus, not a zygote. Sperm are released into the vagina. And fertilisation is the fusion of the nuclei of a male and a female gamete.

    AnswerB: the female gamete has a large store of energy.

    This question turns on exact definitions. "Fusion of two gametes" sounds right, but the definition says it is the nuclei that fuse, one from a male gamete and one from a female.

    Revise this: Human reproduction
28. 28Getting the direction and the place right for gas exchange between a mother and her fetus.[1]
    Show how to do itHide the working

    1. The fetus respires, so it needs oxygen and makes carbon dioxide. Oxygen goes from the mother's blood to the fetus's blood, and carbon dioxide goes the other way.
    2. The exchange happens in the placenta, where the two blood supplies come very close without mixing.
    3. The umbilical cord only carries the fetus's blood to and from the placenta. Nothing is exchanged in the cord itself.

    AnswerA: carbon dioxide from fetus to mother, oxygen from mother to fetus, at the placenta.

    Placenta is where, cord is the connection. The right directions appear with both, so check the last column.

    Revise this: Human reproduction
29. 29Saying what the genetic code is and what it specifies.[1]
    Show how to do itHide the working

    1. DNA carries information as the order of its bases. The sequence of bases is the genetic code.
    2. That order decides the order in which amino acids are joined, and the sequence of amino acids decides which protein is made.

    AnswerC: the code is a sequence of bases, and it codes for a sequence of amino acids.

    Read the column headings first. The right two phrases appear in another row the wrong way round.

    Revise this: How genes make proteins
30. 30Finding the haploid number from a picture of a diploid cell.[1]
    Show how to do itHide the working

    1. Count the chromosomes in the diagram: there are 8. A diploid cell has two of each kind, so that is 4 pairs.
    2. A haploid cell, a gamete, has one from each pair. That is half the diploid number: 8 ÷ 2 = 4.

    AnswerC: 4.

    Diploid is two sets, haploid is one set. Halve the number you counted: do not double it, and do not give the count itself.

    Revise this: Mitosis and meiosis
31. 31Working out a probability from a pedigree chart for a condition caused by a dominant allele.[1]
    Show how to do itHide the working

    1. Call the dominant allele P and the recessive allele p. A cat without the condition must be pp.
    2. X's father has the condition, so he has at least one P. His own mother did not have it, so she was pp and gave him a p. He is Pp.
    3. X's mother does not have the condition, so she is pp.
    4. Pp crossed with pp: the father passes on P half the time and p half the time, and the mother always passes on p. Half the kittens are Pp, with the condition, and half are pp, without.

    AnswerC: 0.50.

    A parent with a dominant condition is not automatically PP. Look at that parent's own parents: an unaffected one proves a hidden recessive allele.

    The brother and sister already born do not change the chance for X. Each kitten is a fresh 50:50.

    Revise this: Inheritance
32. 32Choosing two parent plants for selective breeding.[1]
    Show how to do itHide the working

    1. In selective breeding you pick the parents that already show the features you want.
    2. The farmer wants short plants with strong stems. Type G is the one that varies in height, so take its shortest plant. That is plant 2.
    3. Type H is the one that varies in stem thickness, so take the one with the thicker stem. That is plant 3.

    AnswerC: plant 2 from type G and plant 3 from type H.

    Choose from each type on the feature that varies in that type. All type G plants have thin stems, so the only thing to pick them on is height.

    Revise this: Selective breeding
33. 33Picking the arrow in the nitrogen cycle that shows what denitrifying bacteria do.[1]
    Show how to do itHide the working

    1. Denitrifying bacteria turn nitrate ions in the soil into nitrogen gas, which goes back into the air.
    2. So look for the arrow that starts at nitrate in the soil and ends at nitrogen gas in the air.
    3. The arrow going the other way, from the air down to the soil, is nitrogen fixation. The arrows into nitrate from dead remains and from faeces and urine are decomposition followed by nitrification.

    AnswerD: from nitrate in the soil to nitrogen gas in the air.

    De-nitrifying takes nitrate away. Two arrows sit side by side here pointing opposite ways, so check each arrowhead.

    Revise this: The nitrogen cycle
34. 34Deciding which phases of a population growth curve are shaped by limiting factors.[1]
    Show how to do itHide the working

    1. In the lag and exponential phases there is plenty of food and space, so nothing is holding the population back.
    2. In the stationary phase, births and deaths are equal, because food is running short and predators and disease are taking their toll. In the death phase those same factors make deaths outnumber births.

    AnswerD: stationary and death.

    Exponential growth only happens while nothing is limiting. The moment a limiting factor matters, the curve stops being exponential.

    Revise this: Populations
35. 35Explaining why farmers use herbicides.[1]
    Show how to do itHide the working

    1. Herbicides kill weeds. Weeds compete with the crop for light, water and mineral ions.
    2. With the weeds gone there is less competition, so the crop plants get more of what they need and the yield goes up.

    AnswerA: to increase crop yields by reducing competition between weeds and crop plants.

    Herbicides are for weeds, insecticides are for insects. And nobody farms to decrease a yield, which removes two of the choices at once.

    Revise this: Producing enough food
36. 36Recognising the definition of biodiversity.[1]
    Show how to do itHide the working

    1. Biodiversity is the number of different species that live in an area.
    2. The other three are definitions of other terms from the same topic: a population, an ecosystem and a community.

    AnswerD: the number of different species that live in an area.

    Learn these four definitions as a set. Population is one species, community is all the populations, ecosystem is the community plus its environment.

    Revise this: Habitat destruction
37. 37Putting three steps of eutrophication into order.[1]
    Show how to do itHide the working

    1. It starts with extra nitrate ions washing into the water. Water plants and algae take them in and use them to make amino acids and proteins, so they grow fast. That is step 3.
    2. The plants and algae then die, and decomposers break them down, turning their protein into ammonium ions. That is step 2.
    3. The decomposers respire aerobically and use up the dissolved oxygen. With too little oxygen, fish cannot respire and they die. That is step 1.

    AnswerD: 3, then 2, then 1.

    Growth, then death and decay, then loss of oxygen. The fish are affected last, so any order starting with step 1 is wrong.

    Revise this: Pollution
38. 38Naming the kind of assisted reproduction in which sperm are placed inside the female.[1]
    Show how to do itHide the working

    1. In artificial insemination, sperm are collected and put into the female's uterus. Fertilisation then happens inside her body in the usual way.
    2. In IVF, in vitro fertilisation, eggs are taken out and fertilised by sperm in a dish in a laboratory. It is embryos, not sperm, that are then placed in the uterus.

    AnswerB: artificial insemination, into the uterus.

    "In vitro" means "in glass": fertilisation outside the body. If sperm go into the female, it is insemination.

    Revise this: Conservation
39. 39Choosing the enzyme that belongs in a biological washing powder.[1]
    Show how to do itHide the working

    1. Stains such as blood, egg and grass contain proteins, which do not dissolve in water.
    2. A protease breaks proteins down into small soluble molecules that wash away.

    AnswerD: protease.

    Pectinase is the one used to get more juice out of fruit. DNA ligase joins pieces of DNA in genetic modification.

    Revise this: Biotechnology
40. 40Recognising the use of genetic modification that involves human genes.[1]
    Show how to do itHide the working

    1. Human genes, such as the gene for insulin, are put into bacteria. The bacteria then make the human protein, which can be collected and used as medicine.
    2. The three examples with crop plants use genes from other organisms, not from humans.

    AnswerA: into bacteria to produce proteins.

    The question asks specifically about human genes. All four are real uses of genetic modification, so read for that one word.

    Revise this: Genetic modification

These explanations are Papermunch’s own, written to teach the method. The answers have been checked against the exam board’s mark scheme, which has the final say: open it above. The question paper and mark scheme belong toCambridge University Press & Assessment: each question shown here is drawn from the paper itself as you read, and is not kept on this site.