IGCSE Biology 0610/42 October/November 2025 Past Paper with Answers

Question 1

In the alimentary canal, food is processed by both physical and chemical digestion. Which statement correctly describes what is meant by physical digestion?

1. the breaking up of food into smaller pieces without changing the food molecules chemically
2. the breaking down of large food molecules into smaller molecules by enzymes
3. the movement of digested food molecules from the gut into the blood
4. the removal of undigested food from the body as faeces

Question 2

In the human digestive system, different organs carry out different roles. Which option correctly names the organ where physical digestion occurs by churning, the organ that produces glucagon, and the organ that produces bile?

1. physical digestion occurs in the stomach, glucagon is produced in the pancreas, and bile is produced in the liver
2. physical digestion occurs in the liver, glucagon is produced in the stomach, and bile is produced in the pancreas
3. physical digestion occurs in the pancreas, glucagon is produced in the liver, and bile is produced in the stomach
4. physical digestion occurs in the small intestine, glucagon is produced in the gall bladder, and bile is produced in the pancreas

Question 3

Bile is released into the small intestine and acts on fat. Which option best explains the role of bile in physical digestion?

1. bile emulsifies fat into small droplets, increasing the surface area for lipase to act on
2. bile chemically breaks fat down into fatty acids and glycerol by itself
3. bile neutralises stomach acid so that protease can digest fat
4. bile absorbs the products of fat digestion into the bloodstream

Question 4 · Answer A

Step 1: Incisors are the chisel-shaped front teeth that cut and bite food. Step 2: Molars are the broad back teeth that grind and chew food. Step 3: Teeth do not absorb nutrients, make saliva or store food, so only the first option pairs each tooth with its correct function.

Question 5 · Answer A

Step 1: The tiny folds on the surface cells are microvilli, which greatly increase the surface area for absorbing digested food. Step 2: The wide central vessel is the lacteal, part of the lymphatic system. Step 3: The lacteal absorbs the products of fat digestion, so the first option correctly names and explains both parts.

Question 6 · Answer A

Step 1: Plants are multicellular organisms. Step 2: They are producers, making their own food by photosynthesis using chlorophyll in chloroplasts, and have cellulose cell walls. Step 3: Being single-celled, feeding on others, moving around or having chitin walls describe other kingdoms, not plants.

Question 7 · Answer A

Step 1: The five kingdoms are animal, plant, fungus, protoctist and prokaryote. Step 2: The animal kingdom and the fungus kingdom are two of these, other than plants. Step 3: Leaves and flowers are plant parts, vertebrates and insects are groups within the animal kingdom, and viruses are not placed in a kingdom.

Question 8 · Answer A

Step 1: In a monocotyledon stem the vascular bundles are scattered across the whole cross-section. Step 2: In a dicotyledon stem the vascular bundles are instead arranged in a ring towards the outer edge. Step 3: They are not scattered, not all in the centre, and they are certainly present, so only the ring arrangement is correct.

Question 9 · Answer A

Step 1: In a dicotyledon root the xylem is found in the centre, often in a star shape. Step 2: The phloem lies between the arms of the xylem, around the central xylem. Step 3: Root hairs are extensions of the surface cells that project from the outer edge of the root, so only the first option places all three correctly.

Question 10 · Answer A

Step 1: Xylem transports water and dissolved mineral ions from the roots up the plant. Step 2: The thick walls of xylem vessels also help to support the plant. Step 3: Transport of sucrose and amino acids is the job of phloem, and the other options describe processes xylem does not carry out.

Question 11 · Answer A

Step 1: The girdled trees gave 1796 g of fruit compared with 958 g for the ungirdled trees, so girdling roughly doubled the fruit mass. Step 2: Phloem normally translocates sugars (sucrose) made by the leaves away from the branch towards other parts of the plant. Step 3: Removing the phloem traps these sugars in the branch above the cut, so more sugar is available for the growing fruit, giving a greater fruit mass.

Question 12 · Answer A

Step 1: Pectinase breaks down pectin in the cell walls of the fruit. Step 2: This releases more juice and makes the juice clearer, increasing the yield. Step 3: Protease digests protein, lipase digests fat and catalase breaks down hydrogen peroxide, so none of these is used to make fruit juice.

Question 13 · Answer A

Step 1: A catalyst increases the rate of a chemical reaction. Step 2: It is not used up or chemically changed during the reaction, so it can be used again. Step 3: A catalyst speeds up rather than slows down a reaction, and it does not supply energy, so only the first option is correct.

Question 14 · Answer A

Step 1: Iodine turns blue-black with starch, so a faster loss of the blue-black colour means the amylase has broken down the starch faster. Step 2: At 0 °C the particles have little kinetic energy, so there are few successful collisions between amylase and starch and the reaction is very slow. Step 3: As the temperature rises towards 40 °C the particles gain kinetic energy and collide more frequently and successfully, forming more enzyme-substrate complexes and breaking the starch down faster.

Question 15 · Answer A

Step 1: Enzymes are specific, meaning each enzyme has an active site that fits only its own substrate. Step 2: Protease has an active site shaped for protein, not for starch, so starch cannot bind and no enzyme-substrate complex forms. Step 3: Because the starch is not broken down, it remains present and continues to turn the iodine blue-black at every temperature.

Question 16 · Answer A

Step 1: Each enzyme has an optimum pH at which it works fastest. Step 2: Moving away from this pH slows the enzyme and can denature it, so pH affects enzyme action. Step 3: The colour of the container, the time of day and the mass of the test tube have no effect on the enzyme.

Question 17 · Answer A

Step 1: A primary consumer is the organism that eats the producer. Step 2: The grasshopper feeds directly on grass, which is a producer, so the grasshopper is a primary consumer. Step 3: Grass is the producer, while the grey wolf and steppe eagle feed on other animals, so they are secondary or higher consumers.

Question 18 · Answer A

Step 1: A food chain starts with a producer and the arrows point from food to feeder. Step 2: Grass (producer) is eaten by the grasshopper, which is eaten by the corsac fox, which is eaten by the steppe eagle. Step 3: This gives four trophic levels in the correct order, while the other chains have too few levels or the arrows the wrong way round.

Question 19 · Answer A

Step 1: Energy is transferred along a food chain but a large amount is lost at each trophic level, for example as heat from respiration and in waste. Step 2: This means less energy is passed on to the next level. Step 3: With less energy available, less biomass can be supported, so there are fewer organisms at each higher trophic level.

Question 20 · Answer A

Step 1: A small starting population contains only a little genetic variation. Step 2: Breeding among closely related individuals (inbreeding) increases the chance of harmful recessive alleles pairing up, raising the risk of inherited disease. Step 3: With little variation the species is also less able to adapt to environmental change, so the population is more vulnerable.

Question 21 · Answer A

Step 1: Protecting the habitat and passing laws against hunting keep the horses and their environment safe. Step 2: Monitoring the population and educating local people help conservationists respond to threats and gain support. Step 3: Removing habitat, allowing hunting, adding predators or causing pollution would all harm the population, so only the first option helps maintain it.

Question 22 · Answer A

Step 1: The egg and sperm joining to form a zygote is fertilisation. Step 2: The zygote dividing repeatedly by mitosis to form an embryo is cell division. Step 3: The embryo settling into the uterus lining is implantation, so the order is fertilisation, mitosis, implantation.

Question 23 · Answer A

Step 1: Keeping animals close together uses less land for a given output, so more land is free for other uses. Step 2: It gives a higher yield and a more consistent quality of product, often more cheaply. Step 3: These improve food security and profits, so the first option lists real advantages, while the others describe disadvantages or false claims.

Question 24 · Answer A

Step 1: In intensive systems many animals are kept close together. Step 2: This overcrowding lets bacterial infections spread quickly between animals. Step 3: Antibiotics are used to treat and help prevent these bacterial diseases, so the first option is correct, while antibiotics do not kill viruses or act as vitamins.

Question 25 · Answer A

Step 1: The suggested limit is shown by the line at 50 mg per kg. Step 2: A country uses less than the limit when its 2016 value is below this line. Step 3: Only the fourth and the sixth countries have a 2016 value below the 50 mg line, so they are the two countries below the limit.

Question 26 · Answer A

Step 1: The increase is 400 − 260 = 140 mg per kg. Step 2: Percentage increase = (increase ÷ original) × 100 = (140 ÷ 260) × 100 = 53.846…%. Step 3: Rounded to two significant figures this is 54%.

Question 27 · Answer A

Step 1: A chance mutation in the DNA of some bacteria makes them resistant to the antibiotic. Step 2: When the antibiotic is used it kills the non-resistant bacteria, but the resistant ones survive and reproduce, passing on the resistance allele. Step 3: Over many generations the proportion of resistant bacteria increases, which is natural selection acting on the population.

Question 28 · Answer A

Step 1: The breathing rate returns to its resting value 20 minutes after exercise, and the heart rate falls by 150 − 60 = 90 beats per minute between 20 and 40 minutes. Step 2: During exercise lactic acid builds up in the muscles, creating an oxygen debt, and it is carried in the blood to the liver. Step 3: Breathing stays high to supply oxygen, which is used in aerobic respiration to break down the lactic acid, so the first option is correct throughout.

Question 29 · Answer A

Step 1: Excess amino acids are deaminated, removing their nitrogen-containing part. Step 2: This happens in the liver, where the nitrogen is converted into urea. Step 3: The kidney removes urea from the blood, the lungs deal with carbon dioxide, and the bladder stores urine, so the liver is the organ that produces urea.

Question 30 · Answer A

Step 1: Urea is carried in the blood from the liver to the kidneys. Step 2: The kidneys filter the blood and remove urea, which leaves the body in urine. Step 3: The liver makes urea but does not excrete it, and the pancreas and stomach are part of digestion, so the kidney is the excretory organ for urea.

Question 31 · Answer A

Step 1: Anaerobic respiration in yeast breaks down glucose without oxygen. Step 2: The products are ethanol and carbon dioxide, giving C6H12O6 → 2C2H5OH + 2CO2. Step 3: The equation with oxygen is aerobic respiration, the lactic acid equation (C3H6O3) is anaerobic respiration in muscle, and the reversed equation is not respiration.

Question 32 · Answer A

Step 1: When bread dough is made, yeast respires anaerobically. Step 2: The carbon dioxide it releases forms bubbles that make the dough rise. Step 3: Cheese and butter are dairy products and salt is a mineral, so bread is the product made using yeast.