IGCSE Biology 0610/43 May/June 2025 Past Paper with Answers

Question 1

The human digestive system includes the salivary glands, the oesophagus, the gall bladder and the anus. Which option correctly matches each of these structures to its function?

1. the salivary glands produce amylase, the oesophagus transports food to the stomach, the gall bladder stores bile, and the anus carries out egestion of undigested food
2. the salivary glands store bile, the oesophagus produces amylase, the gall bladder carries out egestion, and the anus transports food to the stomach
3. the salivary glands carry out egestion, the oesophagus stores bile, the gall bladder transports food to the stomach, and the anus produces amylase
4. the salivary glands transport food to the stomach, the oesophagus carries out egestion, the gall bladder produces amylase, and the anus stores bile

Question 2

Chemical digestion takes place in the alimentary canal with the help of enzymes. Which option correctly describes the role of chemical digestion?

1. it breaks large, insoluble molecules down into small, soluble molecules so that they can be absorbed
2. it builds small, soluble molecules up into large, insoluble molecules so that they can be stored
3. it physically breaks food into smaller pieces using the teeth without changing the molecules
4. it removes water from food to make the molecules larger and easier to absorb

Question 3

In the small intestine the sugar maltose is digested by the enzyme maltase. What is the name of the product of this reaction?

1. glucose
2. starch
3. amino acids
4. fatty acids

Question 4 · Answer A

Step 1: Maltase is bound to the membranes of the epithelial cells that line the small intestine, including those covering the villi. Step 2: Maltose is therefore digested as it comes into contact with these cell membranes. Step 3: It is not digested in the stomach, inside red blood cells or in the bile, so the first option is correct.

Question 5 · Answer A

Step 1: The stomach produces acidic gastric juice (hydrochloric acid) giving a very low pH that denatures amylase, changing the shape of its active site so that starch can no longer fit and form enzyme-substrate complexes. Step 2: In the small intestine, bile is released which is alkaline and neutralises the acidic mixture from the stomach. Step 3: This raises the pH to a suitable level for amylase, so amylase can digest starch in the small intestine but not in the acidic stomach.

Question 6 · Answer A

Step 1: A large surface area provides plenty of space for gases to diffuse across. Step 2: A thin wall, often only one cell thick, gives a short diffusion distance for oxygen and carbon dioxide. Step 3: A good blood supply from a network of capillaries keeps a steep concentration gradient, so the first option lists three correct features.

Question 7 · Answer A

Step 1: During inspiration the diaphragm contracts and flattens downwards. Step 2: At the same time the external intercostal muscles contract to pull the ribs up and out. Step 3: The internal intercostal muscles are used in forced breathing out, so during inspiration it is the external intercostals and the diaphragm that contract.

Question 8 · Answer A

Step 1: The cartilage rings are firm and form a support in the wall of the trachea and bronchi. Step 2: This support holds the airway open so air can pass freely, even when pressure inside falls. Step 3: Mucus is made by goblet cells, gas exchange happens in the alveoli, and breathing muscles move air, so keeping the airway open is the role of cartilage.

Question 9 · Answer A

Step 1: Aerobic respiration uses glucose (C₆H₁₂O₆) and oxygen (O₂) as the reactants. Step 2: The products are carbon dioxide (CO₂) and water (H₂O). Step 3: Balancing the atoms gives C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O, with six oxygen molecules, six carbon dioxide and six water molecules.

Question 10 · Answer A

Step 1: Physical activity increases respiration in the muscles, raising the carbon dioxide concentration in the blood. Step 2: The brain detects this high carbon dioxide and sends more nerve impulses to the muscles used in breathing. Step 3: These muscles contract more strongly and more often, and adrenaline may also be released, so the rate and depth of breathing increase.

Question 11 · Answer A

Step 1: When blood glucose rises, the pancreas detects this and releases the hormone insulin. Step 2: Insulin causes the liver to remove glucose from the blood and convert it into glycogen for storage. Step 3: Because the rise in glucose triggers a response that lowers it back to normal, this is an example of negative feedback (homeostasis).

Question 12 · Answer A

Step 1: In type 1 diabetes the pancreas does not make enough insulin, so insulin must be injected to control blood glucose. Step 2: The person also monitors their blood glucose concentration regularly to keep it within safe limits. Step 3: Counting carbohydrates and matching food to activity also help, but antibiotics, extra sugar and painkillers do not treat diabetes, so the first pair is correct.

Question 13 · Answer A

Step 1: Percentage change = (change ÷ original value) × 100, using the value at 5 minutes as the original. Step 2: The change is 120 − 210 = −90 mg per 100 cm³, so the percentage change is (−90 ÷ 210) × 100 = −42.857%. Step 3: Rounded to two significant figures this is a decrease of 43%.

Question 14 · Answer A

Step 1: Adrenaline causes stored glycogen to be broken down into glucose, raising the blood glucose concentration. Step 2: This extra glucose is delivered to the muscles, where it is used in respiration to release energy. Step 3: The energy released is used for muscle contraction, allowing the body to fight or run away quickly, so the first option is the advantage.

Question 15 · Answer A

Step 1: The tall, column-shaped cells packed closely just below the upper surface are the palisade mesophyll, where most photosynthesis takes place, so B is the palisade mesophyll. Step 2: The single layer of cells forming the lower surface of the leaf is the lower epidermis, so C is the lower epidermis. Step 3: Spongy mesophyll has air spaces, and xylem and phloem are transport tissues, so the first option is correct.

Question 16 · Answer A

Step 1: The large air spaces allow gases such as carbon dioxide and oxygen to diffuse through the leaf for photosynthesis and respiration. Step 2: They also make the leaf less dense, providing buoyancy so it floats on the water surface and receives plenty of light. Step 3: Starch storage, water transport, trapping insects and making pigment are not functions of the air spaces, so the first option is correct.

Question 17 · Answer A

Step 1: The green pigment is chlorophyll, found in the chloroplasts of the palisade mesophyll. Step 2: Chlorophyll absorbs (traps) light energy from sunlight. Step 3: This light energy is transferred into chemical energy that is used to synthesise carbohydrates in photosynthesis, so the first option is correct.

Question 18 · Answer A

Step 1: A thick waxy cuticle on a land plant reduces water loss, but a water lily is surrounded by water and does not need to prevent water loss. Step 2: A thin cuticle therefore allows carbon dioxide to enter the leaf more easily and lets more light reach the palisade mesophyll. Step 3: This makes photosynthesis more efficient and saves the plant resources, so the first option explains the adaptation.

Question 19 · Answer A

Step 1: There are 100 mm² in 1 cm², so to change from per mm² to per cm² you multiply by 100. Step 2: 573 × 100 = 57 300. Step 3: So the stomatal density is 57 300 stomata per cm².

Question 20 · Answer A

Step 1: Pondweed is fully submerged, so oxygen and carbon dioxide diffuse straight into the leaf from the surrounding water and no stomata are needed. Step 2: A water lily floats, so only its upper surface is in contact with the air, and that is where its stomata are, allowing gas exchange with the air. Step 3: The lower surface rests on the water, so stomata there would be useless, which is why the water lily has none on its lower surface.

Question 21 · Answer A

Step 1: Monocotyledonous plants typically have long, narrow leaves. Step 2: The veins in these leaves run parallel to one another rather than forming a network. Step 3: Broad leaves with branching veins and flower parts in fours and fives are features of dicotyledons, so the strap-shaped leaves with parallel veins identify rice as a monocotyledon.

Question 22 · Answer A

Step 1: Plant roots take in nitrate ions by active transport, which needs energy from aerobic respiration. Step 2: Low oxygen in waterlogged soil reduces aerobic respiration, so less energy is released for active transport and fewer nitrate ions are absorbed. Step 3: Nitrate ions are needed to make amino acids, so with fewer nitrate ions the plant makes fewer amino acids and less protein.

Question 23 · Answer A

Step 1: Antibiotics are medicines that act against bacteria. Step 2: They kill bacteria or stop them reproducing, which is why they treat bacterial infections. Step 3: Antibiotics do not work against viruses, and they are not used to kill mammals or insects, so bacteria is the correct answer.

Question 24 · Answer A

Step 1: Using antibiotics only when they are truly necessary, such as for serious bacterial infections, reduces how often bacteria are exposed to them. Step 2: Completing the full course ensures all the bacteria are killed, leaving none to develop resistance. Step 3: Overusing antibiotics, stopping early, sharing them or using them for viral illnesses all increase resistance, so the first pair is correct.

Question 25 · Answer A

Step 1: In the binomial system every organism has a two-part scientific name. Step 2: The first word, written with a capital letter, is the genus. Step 3: The second word is the species, so in Penicillium chrysogenum, Penicillium is the genus.

Question 26 · Answer A

Step 1: Thread-like structures called hyphae are characteristic of fungi. Step 2: Cell walls made of chitin, rather than cellulose, are also a feature of fungi. Step 3: Together with reproduction by spores, these features show the organism belongs to the fungi kingdom, not the animals, plants or bacteria.

Question 27 · Answer A

Step 1: Fermenters are used to grow microorganisms that make useful products on a large scale. Step 2: Insulin can be made by genetically modified bacteria grown in a fermenter, as can mycoprotein and ethanol. Step 3: Haemoglobin, starch and cellulose are made inside animals or plants, not produced in a fermenter, so insulin is the correct answer.

Question 28 · Answer A

Step 1: The fungus that produces penicillin respires aerobically and needs a supply of oxygen. Step 2: Oxygen is therefore bubbled into the fermenter to keep the fungus respiring and growing. Step 3: Carbon dioxide is a waste product, while nitrogen and hydrogen are not used for respiration, so the gas needed is oxygen.

Question 29 · Answer A

Step 1: The temperature is kept at a suitable value using a water jacket so the enzymes of the fungus work efficiently without being denatured. Step 2: The pH is kept suitable with a buffer, and nutrients are supplied for the fungus to grow and make penicillin. Step 3: A stirrer keeps the temperature, nutrients and oxygen evenly distributed, and the fermenter is kept sterile, so the first option correctly describes the controlled conditions.

Question 30 · Answer A

Step 1: Yeast is a single-celled fungus that respires anaerobically to produce carbon dioxide and ethanol. Step 2: In bread-making the carbon dioxide makes the dough rise. Step 3: In biofuel production the ethanol made by yeast is collected and used as fuel, so the organism is yeast.

Question 31 · Answer A

Step 1: In 1982 almost the whole island was forested, but by 2013 only small patches of forest remained. Step 2: This shows the area covered by forest has decreased. Step 3: The remaining forest is broken into separate patches, so it has also become more fragmented, making the first option correct.

Question 32 · Answer A

Step 1: Forests are often cleared to make space for agriculture, such as growing crops or grazing animals. Step 2: Trees are also logged (cut down) for timber and for fuel, reducing the forest. Step 3: Planting forests, protecting trees, more rainfall and fewer people would not cause forest loss, so the first pair gives the correct causes.

Question 33 · Answer A

Step 1: Process T takes carbon dioxide from the atmosphere into plants, which is photosynthesis. Step 2: Process U returns carbon dioxide from animals to the atmosphere, which is respiration. Step 3: Process V returns carbon dioxide from burning fossil fuels, which is combustion, so the first option names all three correctly.

Question 34 · Answer A

Step 1: Trees remove carbon dioxide from the atmosphere by photosynthesis, so cutting them down means less carbon dioxide is removed. Step 2: Burning the felled trees or letting them decompose adds even more carbon dioxide to the atmosphere. Step 3: This extra carbon dioxide traps more infrared (heat) radiation from the ground, increasing the greenhouse effect and raising global temperatures.

Question 35 · Answer A

Step 1: Removing forest destroys the habitats of many organisms, which can lead to the extinction of species and a reduction in biodiversity. Step 2: Without tree roots to hold the soil, soil erosion increases, which can cause flooding. Step 3: Increasing habitats, richer soil, cooler temperatures or larger animal populations are not effects of deforestation, so the first option is correct.