0610/22 May/June 2025 Worked Answers (IGCSE Biology 0610 Extended)
40 questions · 40 marks · 45 minutes
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Worked answers for 33 questions
- Step 1: The characteristics of all living organisms are movement, respiration, sensitivity, growth, reproduction, excretion and nutrition. Step 2: Excretion, growth and respiration are each on this list, so three of the processes are characteristics. Step 3: Digestion is only one part of nutrition, not a characteristic in its own right, so the total is 3.Method:Match each process to the list of characteristics of living organisms and count the matches.Examiner tips
- Use MRS GREN: movement, respiration, sensitivity, growth, reproduction, excretion, nutrition.
- Step 1: Compare the sequences base by base and count the differences. Step 2: Species 1 and 3 differ at four positions, which is more than any other pair (1 and 2 differ at three, 3 and 4 at three, 2 and 4 at two). Step 3: The pair with the most differences is the least closely related, so it is species 1 and 3.Method:Count base differences for each pair and choose the pair with the most.Examiner tips
- Most base differences means least closely related.
- Step 1: The organism has a nucleus, so it is not a prokaryote (prokaryotes have no nucleus). Step 2: It is a single cell, so it is not a plant, which is many-celled. Step 3: It has chloroplasts, so it is not a fungus (fungi cannot photosynthesise). A single-celled organism with a nucleus and chloroplasts is a protoctist.Method:Use the features to eliminate each kingdom until only protoctist remains.Examiner tips
- Single-celled organisms with a nucleus are usually protoctists.
- Step 1: A cell is a single unit and a tissue is a group of similar cells, but a leaf contains several different tissues. Step 2: A structure made of several tissues working together for one job is an organ. Step 3: An organ system is several organs together, which is larger than a single leaf, so a leaf is an organ.Method:Place a leaf on the ladder of organisation from cell up to organ system.Examiner tips
- Order of organisation: cell, tissue, organ, organ system, organism.
- Step 1: Actual length = magnified length divided by magnification, so actual length = 5.00 mm divided by 250 = 0.02 mm. Step 2: Converting 0.02 mm to micrometres gives 0.02 × 1000 = 20 µm. Step 3: Written in standard form this is 2.00 × 10¹ µm. Multiplying instead of dividing, or using the wrong power of ten, gives the other answers.Method:Divide image size by magnification, then convert the units to micrometres.Examiner tips
- Actual size = image size / magnification; 1 mm = 1000 µm.
- Step 1: Diffusion is faster when there is a larger surface area to diffuse across. Step 2: It is also faster when the concentration gradient is steeper (a high gradient). Step 3: And it is faster when the distance to travel is shorter. So the fastest diffusion needs a high surface area, a high gradient and a short path.Method:Pick the row where all three factors favour fast diffusion.Examiner tips
- Large surface area, steep gradient and short distance all speed up diffusion.
- Step 1: A cylinder lengthens when water enters its cells by osmosis. Step 2: Water moves in when the surrounding liquid is more dilute than the cell contents, which is true for pure water (1) and the solution less concentrated than the cells (2). Step 3: Liquid 3 is more concentrated, so water leaves and the cylinder shrinks; liquid 4 is the same concentration, so there is no net change.Method:Compare each liquid with the cell contents and pick the ones that are more dilute.Examiner tips
- Pure water and dilute solutions make potato tissue gain water and swell.
- Step 1: Enzymes are made of protein, so they are proteins, not carbohydrates. Step 2: They speed up reactions without being used up, which makes them biological catalysts. Step 3: A substrate is the substance an enzyme acts on, not the enzyme itself, so enzymes are proteins that act as biological catalysts.Method:Recall that enzymes are proteins that catalyse reactions and match the definition.Examiner tips
- Enzyme = protein + biological catalyst.
- Step 1: Lipase is the enzyme that digests fats and oils. Step 2: It breaks oil down into fatty acids and glycerol. Step 3: Protein to amino acids is done by protease, starch to maltose by amylase, and maltose is not turned into starch by a digestive enzyme.Method:Identify the reaction that breaks down a fat or oil, since that is what lipase does.Examiner tips
- Lipase + fats/oils gives fatty acids and glycerol.
- Step 1: Microvilli are tiny folds on the surface of the cells lining the small intestine. Step 2: These folds greatly increase the surface area of the lining. Step 3: A larger surface area means more digested food can be absorbed at once, so microvilli increase the surface area for absorption.Method:Link the folded shape of microvilli to a larger surface area for absorbing food.Examiner tips
- More folds means more surface area for faster absorption.
- Step 1: Xylem vessels have thick walls strengthened with lignin, which support the plant and stop the vessels collapsing. Step 2: Mature xylem vessels are dead, empty tubes with no living contents. Step 3: Because they are dead, they contain no mitochondria, so xylem vessels have thick walls and no mitochondria.Method:Recall that xylem vessels are dead, thick-walled tubes and match the features.Examiner tips
- Xylem = thick lignified walls + dead empty cells (no mitochondria).
- Step 1: The water lost from each tube was taken up by the plant and transpired. Tube X lost 5.7 g but tube Y lost only 1.6 g, so tube Y transpired less. Step 2: The plastic bag traps water vapour around the leaves, which raises the humidity. Step 3: Higher humidity reduces the difference in water vapour between the leaf and the air, so transpiration is slower in tube Y.Method:Compare the water lost in each tube, then explain the lower loss using humidity.Examiner tips
- A plastic bag traps water vapour, raising humidity and slowing transpiration.
- Step 1: In a double circulation, blood passes through the heart twice for each complete circuit of the body. Step 2: The heart pumps the blood again before sending it to the body, so it reaches the body cells at high pressure. Step 3: This delivers oxygen quickly. Mixing of blood is actually prevented, the pressure in the lungs is kept low to protect the capillaries, and carbon dioxide removal is not reduced.Method:Recall that the heart re-pumps blood, raising the pressure to the body, and pick that advantage.Examiner tips
- Double circulation means blood is repressurised before going to the body.
- Step 1: The septum is the wall of muscle running down the middle of the heart. Step 2: It keeps the left side, carrying oxygenated blood, completely separate from the right side, carrying deoxygenated blood. Step 3: The valves control the direction of blood flow between chambers, and the atrium wall is just part of one chamber, so they do not separate the two types of blood.Method:Identify the central dividing wall of the heart.Examiner tips
- The septum is the central wall keeping the two sides of the heart apart.
- Step 1: Veins carry blood back to the heart at low pressure, so they do not need thick walls; their walls are thin compared with the vessel diameter. Step 2: They have a large lumen to let blood flow back easily. Step 3: They contain valves to stop the low-pressure blood flowing backwards, so a vein has a thin wall, a large lumen and valves present.Method:Recall that veins carry low-pressure blood and match the three features.Examiner tips
- Vein = thin wall, large lumen, valves present (low pressure).
- Step 1: Antibodies passed from mother to baby in breast milk give passive immunity, so statement 1 is correct. Step 2: Passive immunity is short-term and makes no memory cells, so statement 2 is wrong. Step 3: Vaccination introduces antigens that make the body produce its own antibodies and memory cells, which is active immunity, so statement 3 is correct. Only 1 and 3 are correct.Method:Judge each statement against the definitions of active and passive immunity.Examiner tips
- Passive = ready-made antibodies, short-term; active = your own antibodies and memory cells.
- Step 1: The depth of each breath is the total volume of air divided by the breathing rate. Step 2: Between 0 and 10 minutes the rate stays at 12 breaths per minute, but the total volume rises from 5000 to 15000 cm3, so each breath must be deeper. Step 3: Therefore the depth of breathing increases in that period; the rate clearly does change from 10 to 20 minutes, and the depth does not fall from 15 to 20 minutes.Method:Calculate the depth per breath at each time and compare across the intervals.Examiner tips
- Same rate but more total air means deeper breaths.
- Step 1: Glucose is a simple sugar made of carbon, hydrogen and oxygen. Step 2: Each glucose molecule contains 6 carbon atoms, 12 hydrogen atoms and 6 oxygen atoms. Step 3: So its chemical formula is C6H12O6; the other formulae have the wrong number of hydrogen or carbon atoms.Method:Recall the number of each atom in glucose and pick the matching formula.Examiner tips
- Remember glucose as C6H12O6 (6 carbon, 12 hydrogen, 6 oxygen).
- Step 1: During the race the muscles respired anaerobically and produced lactic acid, which causes the oxygen debt. Step 2: To repay the debt, the extra oxygen taken in is used to break down the lactic acid. Step 3: Breaking it down using oxygen is aerobic respiration of lactic acid, so that is what happens at X.Method:Identify what the extra oxygen is used for and whether the process is aerobic or anaerobic.Examiner tips
- Oxygen debt is repaid by aerobic breakdown of the lactic acid.
- Step 1: Excess amino acids cannot be stored, so they are broken down in the liver in a process called deamination. Step 2: Deamination produces urea, so urea is made in the liver. Step 3: The kidney removes urea from the blood and the bladder stores urine, but neither produces urea, and the pancreas makes enzymes and hormones.Method:Recall where amino acids are broken down to form urea.Examiner tips
- Urea is made in the liver, then removed by the kidneys.
- Step 1: Glucagon is a hormone that raises blood glucose when it gets too low. Step 2: It is made and released by the pancreas. Step 3: The adrenal gland makes adrenaline, the ovary makes oestrogen, and the liver responds to glucagon by changing glycogen to glucose but does not make the hormone.Method:Recall which gland controls blood glucose by producing insulin and glucagon.Examiner tips
- The pancreas makes both insulin and glucagon to control blood glucose.
- Step 1: The seedling is underground in the dark, so there is no light to cause phototropism. Step 2: The responses must therefore be to gravity, which is gravitropism. Step 3: The shoot grows up, away from gravity, and the root grows down, towards gravity, so both the root and the shoot show gravitropism and neither shows phototropism.Method:Note that the seedling is in the dark, so the responses are to gravity for both organs.Examiner tips
- No light means the response is to gravity (gravitropism).
- Step 1: The increase in the number of people is 6200 minus 1300, which is 4900. Step 2: Percentage increase = increase divided by the original number, times 100, so it is 4900 divided by 1300, times 100. Step 3: This gives 376.9, which is 377% to the nearest whole number.Method:Find the increase, divide by the original number and multiply by 100.Examiner tips
- Always divide the increase by the ORIGINAL value to find percentage increase.
- Step 1: Asexual reproduction involves only one parent and no gametes, so there is no fusion of gamete nuclei. Step 2: The offspring are produced by mitosis, so they are genetically identical to the parent and to each other. Step 3: Being genetically identical means there is no genetic variety, so asexual reproduction has no fusion of gamete nuclei and no genetic variety.Method:Recall that asexual reproduction makes identical clones from one parent without gametes.Examiner tips
- Asexual = one parent, no gametes, identical offspring.
- Step 1: Pollen is made in the anther and lands on the stigma, so transfer is always from anther to stigma. Step 2: Cross-pollination means the pollen lands on a different plant of the same species. Step 3: So it is the transfer of pollen from the anther of one plant to the stigma of a different plant; transfer on the same plant is self-pollination.Method:Check the direction (anther to stigma) and that it is between different plants.Examiner tips
- Cross-pollination: anther of one plant to stigma of another.
- Step 1: Menstruation is the breakdown and loss of the lining of the uterus through the vagina. Step 2: Ovulation is the release of an egg from an ovary, not menstruation. Step 3: The fusion of nuclei is fertilisation, and the start of puberty is not a single process in the cycle, so only menstruation linked to shedding the uterus lining is correct.Method:Match each process to its correct definition in the menstrual cycle.Examiner tips
- Menstruation = shedding the uterus lining; ovulation = releasing an egg.
- Step 1: An allele is a version of a gene, and a new allele needs a change in the DNA. Step 2: A mutation is a random change in a gene, so it is the way new alleles are formed. Step 3: Artificial and natural selection only choose between alleles that already exist, and sexual reproduction shuffles existing alleles without creating new ones.Method:Recall that new alleles require a change in the gene, which is a mutation.Examiner tips
- Only mutation creates brand-new alleles.
- Step 1: In artificial selection, humans choose which organisms breed, so survival does not depend on competing for resources. Step 2: In natural selection, organisms must compete to survive and reproduce. Step 3: Both types change characteristics, both rely on existing genetic variation, and both act over many generations, so the real difference is the lack of competition in artificial selection.Method:Pick the feature that is true only for artificial selection, where humans control breeding.Examiner tips
- Artificial selection is run by humans, so there is no struggle to survive.
- Step 1: A xerophyte must conserve water, so its thick waxy layer reduces (stops) water evaporation from the surface. Step 2: It also needs to gather as much water as possible, so it has extensive root systems to maximise water uptake. Step 3: Labels that increase evaporation or restrict and minimise uptake would lose water or fail to collect it, which would not suit a dry habitat.Method:Choose the labels where both adaptations help the plant save and collect water.Examiner tips
- Xerophyte = waxy layer to cut water loss + extensive roots to gather water.
- Step 1: Energy enters a food chain as light, which plants capture during photosynthesis. Step 2: Plants store this energy as chemical energy in food. Step 3: When organisms are eaten, the energy passes along the chain as chemical energy in food; heat is lost to the surroundings rather than transferred between organisms.Method:Identify how energy first enters (light) and how it moves between organisms (chemical).Examiner tips
- Light energy in; chemical energy passed along the chain; heat is lost.
- Step 1: Nitrifying bacteria in the soil change ammonium ions into nitrate ions. Step 2: This conversion of ammonium to nitrate is called nitrification. Step 3: Decomposition releases ammonium from dead matter, denitrification turns nitrate back into nitrogen gas, and nitrogen fixation turns nitrogen gas into nitrogen compounds, so none of these match.Method:Match the conversion of ammonium to nitrate with its named process.Examiner tips
- Nitrification: ammonium to nitrate, carried out by nitrifying bacteria.
- Step 1: A sustainable resource is one that is not used up, so enough fish must be left to breed and replace those caught. Step 2: Smaller fish are usually younger and have not yet bred. Step 3: Leaving the smaller fish lets them grow and reproduce, keeping the population going, so this is the reason linked to sustainability; ease of catching and price are only economic reasons.Method:Choose the reason that keeps enough breeding fish in the population.Examiner tips
- Leave the young fish to breed so the stock can replace itself.
- Step 1: Bacteria are useful because they reproduce rapidly, giving huge numbers quickly (feature 4). Step 2: They can also be used to make complex and useful molecules such as proteins (feature 3). Step 3: Being unaffected by antibiotics is not a useful feature, and bacteria do contain plasmids, which are actually used in genetic engineering, so feature 2 is false.Method:Pick the two true, useful features and reject the false or unhelpful ones.Examiner tips
- Bacteria are useful because they breed fast and can be made to produce useful molecules.
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