IGCSE Biology 0610/23 October/November 2025 Past Paper with Answers

Question 1

Which of the following is a characteristic shown by all living organisms?

1. reproduction
2. breathing
3. photosynthesis
4. transpiration

Question 2

Organisms are named using the binomial system, which gives each organism a two-part scientific name. What are the two parts of this name, in the correct order?

1. the genus followed by the species
2. the genus followed by the kingdom
3. the kingdom followed by the genus
4. the kingdom followed by the species

Question 3

A palisade cell from a leaf and a neurone from a human are both observed under a light microscope. Which cell component would be found only in the palisade cell and not in the neurone?

1. cell wall
2. cell membrane
3. cytoplasm
4. nucleus

Question 4 · Answer A

Step 1: The wall surrounds the lumen on both sides, so the lumen diameter is the external diameter minus twice the wall thickness: 36 minus (2 times 9) = 36 minus 18 = 18 mm. Step 2: Convert millimetres to micrometres by multiplying by 1000: 18 mm = 18 000 micrometres. Step 3: So the diameter of the lumen is 18 000 micrometres.

Question 5 · Answer A

Step 1: In diffusion, particles spread out from where they are crowded together to where there are fewer of them. Step 2: This means net movement is from a higher concentration to a lower concentration. Step 3: Moving from high to low concentration is moving down the concentration gradient, so the correct words are higher, lower and down.

Question 6 · Answer A

Step 1: A cylinder gains water when it gets longer, so the ratio of final length to initial length is greater than 1.0. Step 2: The ratio is above 1.0 only at 0.1 (1.1) and 0.2 (1.05) moles per dm3. Step 3: At 0.3 the length is unchanged (1.0) and at 0.4 and 0.5 the ratio is below 1.0, so water was lost there; therefore the cells gained water at 0.1 and 0.2 moles per dm3.

Question 7 · Answer A

Step 1: Oil is a fat, and the enzyme that digests fats is lipase; trypsin is a protease and cannot break down oil. Step 2: Breaking the oil into many small drops gives the largest total surface area for the lipase to act on. Step 3: The fastest digestion therefore needs both lipase and the largest surface area, which is many small drops with lipase.

Question 8 · Answer A

Step 1: Plants need magnesium ions to make chlorophyll, the green pigment used in photosynthesis. Step 2: Chlorophyll therefore contains magnesium. Step 3: Cellulose, glucose and glycerol are carbohydrates or lipid building blocks that contain only carbon, hydrogen and oxygen, so they do not contain magnesium.

Question 9 · Answer A

Step 1: Xylem carries water and is found inside the vein (vascular bundle) on the upper side, nearer the top of the leaf. Step 2: The tissue on the lower side of the vein that carries sugars is the phloem. Step 3: The tall cells just below the upper surface are palisade mesophyll and the rounded cells with air spaces are spongy mesophyll, so the xylem is the water-carrying tissue on the upper side of the vein.

Question 10 · Answer A

Step 1: In the dark the leaf cannot photosynthesise, so it only respires, taking in oxygen and releasing carbon dioxide. Step 2: The carbon dioxide given out is absorbed by the chemical, so the total volume of gas falls as oxygen is used up. Step 3: The falling gas volume lowers the pressure inside the tube, so the ink drop is drawn towards the leaf; the reason is respiration.

Question 11 · Answer A

Step 1: Chemical digestion uses enzymes to break large insoluble molecules into smaller soluble ones. Step 2: Breaking starch down into reducing sugars is done by the enzyme amylase, so it is chemical digestion. Step 3: Churning by the stomach, grinding by teeth and mixing with bile are all physical (mechanical) processes that do not break chemical bonds within food molecules.

Question 12 · Answer A

Step 1: The single vessel in the centre of a villus is the lacteal, which is part of the lymphatic system. Step 2: The lacteal absorbs the products of fat digestion, which are fatty acids and glycerol. Step 3: The blood capillaries around the outside absorb amino acids and glucose, so the central lacteal absorbs fatty acids and glycerol.

Question 13 · Answer A

Step 1: Transpiration is the loss of water vapour from the leaves, and it speeds up when the air can take up water quickly. Step 2: Low humidity steepens the water-vapour gradient, wind carries the vapour away, and high temperature increases evaporation. Step 3: So the fastest transpiration occurs with low humidity, windy conditions and a high temperature.

Question 14 · Answer A

Step 1: A source makes or releases sucrose and a sink uses or stores it. Step 2: Roots store and use sugars, so they act as sinks (statement 2 correct), and spongy mesophyll cells photosynthesise, so they can act as sources (statement 4 correct). Step 3: Palisade cells photosynthesise and so act as sources, not only sinks (statement 1 wrong), and phloem transports sucrose and amino acids, not just glucose (statement 3 wrong); so only 2 and 4 are correct.

Question 15 · Answer A

Step 1: Veins carry blood back to the heart at low pressure, so they contain valves to stop the blood flowing backwards. Step 2: A one-cell-thick wall is a feature of capillaries, not veins. Step 3: A narrow lumen and thick muscular walls are features of arteries, so the correct feature of veins is that valves are present.

Question 16 · Answer A

Step 1: Atrioventricular valves lie between an atrium and the ventricle below it. Step 2: The atrioventricular valve in the right side of the heart is the one between the right atrium and the right ventricle. Step 3: The valve between the left atrium and left ventricle is on the left side, and the valves at the base of the aorta and pulmonary artery are semilunar valves, not atrioventricular valves.

Question 17 · Answer A

Step 1: Active immunity is when the body makes its own antibodies in response to an antigen. Step 2: Producing antibodies after an infection means the person has made the antibodies themselves, so this is active immunity. Step 3: Antibodies passed in breast milk, across the placenta, or given by injection are made by someone else, so these are examples of passive immunity.

Question 18 · Answer A

Step 1: During expiration the chest volume must decrease. Step 2: The external intercostal muscles relax so the ribs move down and in, and the diaphragm relaxes and moves up into a dome shape. Step 3: Both changes reduce the volume of the chest, raising the pressure and pushing air out, so expiration involves the intercostals relaxing and the diaphragm relaxing and moving up.

Question 19 · Answer A

Step 1: Urea is made in the liver, so the pathway must start at the liver, and it is excreted at the kidney, so it must end there. Step 2: Blood leaves the liver in the hepatic vein, travels to the heart and lungs and back to the heart. Step 3: It then leaves the heart and reaches the kidney through the renal artery, so the route is liver, hepatic vein, heart, lungs, heart, renal artery, kidney.

Question 20 · Answer A

Step 1: To focus on a near object the lens must become thicker and more curved. Step 2: The ciliary muscles contract, which makes the ring of muscle smaller and slackens the suspensory ligaments. Step 3: With the ligaments slack the lens is no longer pulled thin and becomes fatter, so for a near object the ciliary muscles are contracted and the suspensory ligaments are slack.

Question 21 · Answer A

Step 1: An arriving impulse first triggers the release of neurotransmitter into the gap (event 2). Step 2: The neurotransmitter then diffuses across the gap (event 4) and binds with receptor proteins on the next neurone (event 3). Step 3: This binding starts a new impulse in the next neurone (event 1), giving the order 2, 4, 3, 1.

Question 22 · Answer A

Step 1: To avoid getting too cold the body must make more heat and lose less heat. Step 2: Shivering makes the muscles contract rapidly, releasing heat, while vasoconstriction reduces blood flow to the skin surface so less heat is lost. Step 3: Sweating and vasodilation both increase heat loss, so they would cool the body further; the correct pair is shivering and vasoconstriction.

Question 23 · Answer A

Step 1: The gland in the upper abdomen behind the stomach is the pancreas. Step 2: The pancreas secretes insulin, which lowers blood glucose concentration. Step 3: Adrenaline is made by the adrenal glands above the kidneys, oestrogen by the ovaries and testosterone by the testes, so the gland behind the stomach secretes insulin.

Question 24 · Answer A

Step 1: Hormonal control uses chemicals carried in the blood, so it acts slowly but its effects last a long time. Step 2: Nervous control uses electrical impulses, so it acts very fast but its effects are short-lived. Step 3: The only fully correct row is therefore hormonal control being slow to act with a long-lasting effect.

Question 25 · Answer A

Step 1: Auxin is made in the shoot tip (statement 3 correct) and moves to the shaded or lower side of a shoot or stem. Step 2: In a horizontal stem it gathers on the lower side (statement 1 correct), and it gathers on the darker side, not the side with more light (statement 2 wrong). Step 3: Auxin promotes cell elongation rather than preventing it (statement 4 wrong), so only statements 1 and 3 are correct.

Question 26 · Answer A

Step 1: Antibiotics kill or stop the growth of bacteria but have no effect on viruses. Step 2: Cholera is caused by a bacterium, so it can be treated with antibiotics. Step 3: HIV is a virus and so cannot be treated with antibiotics, rickets is caused by a lack of vitamin D rather than a pathogen, and not all pathogen diseases are bacterial, so "all diseases caused by pathogens" is wrong.

Question 27 · Answer A

Step 1: Both methods are sexual reproduction involving gametes, so offspring show variation; self-pollination does not give genetically identical offspring, so conclusion 1 is wrong. Step 2: Cross-pollination mixes genes from two different plants, giving genetically different offspring (conclusion 2 correct). Step 3: This greater variation increases the chance that some offspring can adapt to changes in their surroundings (conclusion 3 correct), so only conclusions 2 and 3 are right.

Question 28 · Answer A

Step 1: The umbilical artery carries blood from the fetus to the placenta, so it has used up oxygen and has a low oxygen concentration. Step 2: The umbilical vein carries blood from the placenta back to the fetus after waste has been removed, so it has a low urea concentration. Step 3: The other rows are wrong because the umbilical artery is low in nutrients and high in carbon dioxide and urea, while the umbilical vein is high in nutrients and low in carbon dioxide.

Question 29 · Answer A

Step 1: During pregnancy the placenta takes over the production of progesterone. Step 2: Progesterone maintains the lining of the uterus so that the pregnancy can continue. Step 3: FSH and LH are produced by the pituitary gland and testosterone by the testes, so the hormone made by the placenta is progesterone.

Question 30 · Answer A

Step 1: A gene is a length of DNA that codes for a particular feature. Step 2: Alleles are different forms, or versions, of the same gene that can produce different versions of a characteristic. Step 3: A pair of chromosomes, the number of genes on a chromosome, and two genes side by side are all different ideas, so alleles are different versions of the same gene.

Question 31 · Answer A

Step 1: Polydactyly is dominant, so a cat with no extra toes must have two recessive alleles. Step 2: Crossing two heterozygous cats gives offspring in the ratio 1 homozygous dominant : 2 heterozygous : 1 homozygous recessive. Step 3: Only the homozygous recessive cat has no extra toes, which is 1 out of 4, so the probability is 0.25.

Question 32 · Answer A

Step 1: Red-green colour blindness is a sex-linked condition controlled by a recessive allele carried on the X chromosome. Step 2: Because males have only one X chromosome, a single recessive allele makes them colour blind, so it is more common in males than females. Step 3: It is not codominance, it can still occur in females who inherit two recessive alleles, and it is more common in males, so the correct statement is that the recessive allele is on an X chromosome.

Question 33 · Answer A

Step 1: Meiosis produces haploid cells, the gametes (feature 1 correct), and halves the chromosome number, so it is a reduction division (feature 3 correct). Step 2: Meiosis shuffles the genetic material, so the cells produced are genetically different and show variation (feature 4 correct). Step 3: Feature 2 is wrong because producing genetically identical cells is a feature of mitosis, so meiosis is associated with features 1, 3 and 4.

Question 34 · Answer A

Step 1: A characteristic that increases an organism’s chances of surviving and reproducing in its environment is called an adaptive feature. Step 2: Competition is the struggle between organisms for limited resources, not a characteristic. Step 3: An observable feature is any visible characteristic and a phenotype is the set of an organism’s characteristics, so the correct term is adaptive feature.

Question 35 · Answer A

Step 1: In the carbon cycle, carbon dioxide is taken out of the air by green plants. Step 2: Plants use carbon dioxide in photosynthesis to make glucose, so photosynthesis removes carbon dioxide from the atmosphere. Step 3: Combustion, decomposition and respiration all release carbon dioxide into the air, so they add it rather than remove it.

Question 36 · Answer A

Step 1: The conversion of ammonia into nitrate ions in the soil is carried out by nitrifying bacteria, so process X is nitrification. Step 2: The conversion of nitrogen gas from the air into compounds that plants can use is carried out by nitrogen-fixing bacteria, so process Y is nitrogen fixation. Step 3: Deamination breaks down amino acids and denitrification returns nitrogen gas to the air, so neither fits these arrows; X is nitrification and Y is nitrogen fixation.

Question 37 · Answer A

Step 1: A full sigmoid curve has four phases: lag, exponential (log), stationary and death. Step 2: The graph shows the slow start (lag phase) and the steep rise (exponential phase). Step 3: Because the line is still rising steeply and has not levelled off or fallen, the stationary phase and the death phase are not shown.

Question 38 · Answer A

Step 1: Herbivores eat producers (plants), so they are the first animals in a food chain. Step 2: The trophic level of organisms that eat producers is called the primary consumer level. Step 3: Secondary, tertiary and quaternary consumers are higher levels that eat other animals, so herbivores are primary consumers.

Question 39 · Answer A

Step 1: Fertiliser adds nutrients that make microorganisms multiply, so bacteria increase and use up oxygen during respiration. Step 2: These changes begin where the fertiliser first enters the river. Step 3: So the entry point is just before the bacteria begin to rise and the dissolved oxygen begins to fall; the maximum bacteria, lowest oxygen and recovery points are all further downstream.

Question 40 · Answer A

Step 1: First the insulin gene must be cut out of a human chromosome using an enzyme (step 2), then placed into a bacterial plasmid (step 3). Step 2: The modified bacteria then reproduce rapidly to make many copies (step 4). Step 3: Finally the insulin they make is removed from the culture (step 1), so the order is 2, 3, 4, 1.