References only, not question text. Open Official paper ↗ where Cambridge publishes the paper,
or see the official Cambridge past-papers page; for other papers, ask your
school. “Paper 42” means Paper 4, variant 2.
Practice questions
Original questions written by HomiLabs in the style of the exam, with answers and mark schemes. They are not
Cambridge past paper questions and have not been reviewed by Cambridge. Try each one before opening the answer.
Q1Variation & mutation · Core · Paper 2 style · 1 mark
(a)Which is an example of discontinuous variation in humans?[1]
Show answer
(a) C ABO blood group
ABO blood group has a few distinct categories with no intermediates and is controlled by genes only. Height, mass and hand span show a continuous range.
Q2Variation & mutation · Core · Paper 4 style · 4 marks
(a)Describe two differences between continuous and discontinuous variation.[2]
(b)Give one example of each type of variation in plants.[2]
Show answer
(a) continuous shows a range of values with intermediates, discontinuous has a few distinct categories; continuous is caused by genes and environment, discontinuous mostly by genes only
B1 range vs distinct groups; B1 genes and environment vs genes alone (or many genes vs one/few genes).
(b) continuous: leaf length / plant height / mass of seeds; discontinuous: flower colour in some species / seed shape (round or wrinkled in peas)
B1 each.
Q3Variation & mutation · Standard · Paper 2 style · 1 mark
(a)Which statement about mutation is correct?[1]
Show answer
(a) B A mutation is a genetic change, and its rate is increased by ionising radiation.
A mutation is a genetic change; ionising radiation and some chemicals increase the rate. Mutations are random (C is wrong) and many are neutral or rarely beneficial (A is wrong).
Q4Variation & mutation · Standard · Paper 4 style · 5 marks
(a)The hand spans, in cm, of twelve students in a class in Multan were:18.5, 19.0, 20.5, 17.0, 21.5, 19.5, 22.0, 18.0, 20.0, 19.5, 21.0, 16.5Calculate the mean hand span to one decimal place and the range.[3]
(b)State the type of variation shown by hand span and the type of graph you would use to display the data for a larger class.[2]
Show answer
(a) mean 19.4 cm; range 5.5 cm
M1 sum 233.0 ÷ 12; A1 19.4 cm; B1 range 22.0 − 16.5 = 5.5 cm.
(b) continuous variation; histogram
B1 each.
Q5Variation & mutation · Standard · Paper 4 style · 3 marks
(a)Identical twins have the same genes. Two identical twin sisters were brought up in different countries; at age 30 one had a body mass of 58 kg and the other 71 kg. Explain this difference.[2]
(b)Suggest one feature that would be the same in both twins whatever their environment.[1]
Show answer
(a) the difference must be caused by the environment, e.g. different diet or amount of exercise
B1 environment; B1 example (diet / exercise / lifestyle).
Q6Variation & mutation · Standard · Paper 6 style · 6 marks
A student measured the lengths, to the nearest mm, of 20 leaflets from one neem tree:42, 55, 61, 48, 53, 58, 66, 51, 47, 59, 63, 54, 50, 57, 45, 62, 52, 56, 49, 60
(a)Sort the lengths into the classes 40–44, 45–49, 50–54, 55–59, 60–64 and 65–69 mm and state the frequency of each class.[3]
(b)State the type of graph that should be drawn and give two rules for drawing it.[2]
B3 all six correct; B2 four or five correct; B1 two or three correct.
(b) histogram; bars touching, equal class widths, frequency on y-axis, classes labelled on x-axis
B1 histogram; B1 any one correct rule.
(c) continuous
B1.
Q7Variation & mutation · Challenge · Paper 4 style · 6 marks
(a)Define gene mutation.[1]
(b)Explain why mutation is important for evolution.[2]
(c)Name two processes, other than mutation, that produce genetic variation in sexually reproducing organisms.[2]
(d)State one factor that increases the rate of mutation.[1]
Show answer
(a) a random change in the base sequence of DNA (of a gene)
B1.
(b) mutation is the only source of new alleles; this creates new variation on which natural selection can act
B1 new alleles; B1 variation for natural selection.
(c) meiosis; random fertilisation (also random mating)
B1 each.
(d) ionising radiation (e.g. X-rays, gamma rays) / certain chemicals
B1.
Q8Adaptive features (xerophytes, hydrophytes) · Core · Paper 2 style · 1 mark
(a)Which feature helps a xerophyte to reduce water loss?[1]
Show answer
(a) D a thick, waxy cuticle
A thick waxy cuticle reduces evaporation of water from the leaf surface. Large air spaces are a hydrophyte feature (buoyancy), and stomata on the upper surface are found in floating leaves.
Q9Adaptive features (xerophytes, hydrophytes) · Core · Paper 4 style · 2 marks
(a)Define the term adaptive feature.[1]
(b)Define the term fitness, as used in biology.[1]
Show answer
(a) an inherited feature that helps an organism to survive and reproduce in its environment
B1.
(b) the probability of an organism surviving and reproducing in the environment in which it is found
B1.
Q10Adaptive features (xerophytes, hydrophytes) · Core · Paper 4 style · 3 marks
(a)The snow leopard lives in the cold, rocky mountains of northern Pakistan. State three adaptive features you would expect it to have and explain how each helps it survive.[3]
Show answer
(a) thick fur – insulation / reduces heat loss; large, furry paws – spread weight on snow and grip; long tail – balance on rocky slopes / wraps around body for warmth; pale, spotted coat – camouflage for hunting; small rounded ears – less heat loss
1 mark each for any three features with a correct explanation.
Q11Adaptive features (xerophytes, hydrophytes) · Standard · Paper 2 style · 1 mark
(a)[1]
Show answer
(a) A on the upper surface, because the lower surface is in contact with water
The lower surface of a floating leaf touches the water, so gas exchange with the air can only happen through stomata on the upper surface. Water loss is not a problem for a hydrophyte, so B is wrong.
Q12Adaptive features (xerophytes, hydrophytes) · Standard · Paper 4 style · 6 marks
(a)Cacti grow in the Thar desert, where rainfall is low and temperatures are high. Explain how three features of a cactus help it to survive in these conditions.[6]
Show answer
(a) leaves reduced to spines – small surface area so less transpiration (also protect from grazers); thick fleshy stem – stores water; thick waxy cuticle – reduces evaporation; few / sunken stomata – less water vapour lost; shallow, widespread roots – absorb rain quickly over a large area (or deep roots reaching ground water); green stem – photosynthesis without leaves
For each of three features: B1 feature, B1 matching explanation (max 6).
Q13Adaptive features (xerophytes, hydrophytes) · Standard · Paper 4 style · 4 marks
(a)The lotus is a hydrophyte rooted in the mud of ponds. Its leaf stalks and stems contain large air spaces. Explain two advantages of these air spaces.[2]
(b)Hydrophytes have very little xylem tissue compared with land plants. Suggest why.[2]
Show answer
(a) keep leaves buoyant / afloat so they reach the light for photosynthesis; allow oxygen to diffuse to roots and stems in the mud (which is low in oxygen)
B1 each.
(b) they are surrounded by water / supported by water, so need little xylem for support; water can be absorbed over the surface, so little transport of water is needed
B1 support from water / little need for lignified support; B1 less need to transport water.
Q14Adaptive features (xerophytes, hydrophytes) · Standard · Paper 6 style · 4 marks
(a)A student peels the lower epidermis from a leaf and counts the stomata in the circular field of view of a microscope. The diameter of the field of view is 0.4 mm and 18 stomata are seen.Calculate the number of stomata per mm². Use area = πr². Give your answer to the nearest whole number.[3]
(b)Suggest how the student could make the estimate more reliable.[1]
Show answer
(a) 143 per mm²
M1 r = 0.2 mm; M1 area = π × 0.2² = 0.126 mm²; A1 18 ÷ 0.126 = 143 per mm².
(b) count stomata in several fields of view (at different places on the leaf / different leaves) and calculate a mean
B1.
Q15Adaptive features (xerophytes, hydrophytes) · Standard · Paper 4 style · 3 marks
(a)Water hyacinth is a hydrophyte that floats on canals and lakes in Pakistan. Its leaf stalks are swollen and spongy, and it has long, feathery roots hanging in the water. Suggest how each of these features helps the plant to survive.[2]
(b)Suggest one reason why a hydrophyte does not need a thick waxy cuticle.[1]
Show answer
(a) swollen spongy stalks contain air spaces that keep the plant afloat in the light; feathery roots give a large surface area to absorb mineral ions (and anchor / balance)
B1 each.
(b) it has plenty of water, so reducing water loss is not important
B1.
Q16Adaptive features (xerophytes, hydrophytes) · Challenge · Paper 4 style · 6 marks
The mean number of stomata per mm² on each surface of the leaves of three plants was counted.plant | upper surface | lower surfacewater lily (floating leaves) | 460 | 0bean (garden plant) | 40 | 280desert grass (leaf rolls up in dry weather, outer surface = lower) | 120 (inner) | 0 (outer)
(a)Calculate how many times more stomata are on the lower surface than on the upper surface of the bean leaf.[1]
(b)Explain the distribution of stomata in the water lily.[2]
(c)When the desert grass leaf rolls up, the stomata face the inside of the roll. Explain how this reduces water loss.[3]
Show answer
(a) 7 times
B1 280 ÷ 40 = 7.
(b) all on upper surface because lower surface is on the water and cannot exchange gases with the air; water loss is not a problem so many stomata can face the air
B1 lower surface in water / no air contact; B1 upper surface exposed to air for gas exchange.
(c) humid / moist air is trapped inside the roll; this reduces the concentration gradient of water vapour between the leaf air spaces and the air outside the stomata; less diffusion of water vapour, so lower transpiration
B1 traps water vapour / humid air; B1 smaller water vapour concentration gradient; B1 slower diffusion / less transpiration. Do not credit 'water' diffusing out instead of water vapour.
Q17Adaptive features (xerophytes, hydrophytes) · Challenge · Paper 4 style · 4 marks
(a)Some xerophytes have their stomata sunken in pits, with many hairs on the leaf surface. Explain how these features reduce the rate of transpiration.[3]
(b)Suggest one disadvantage to a xerophyte of having very few stomata.[1]
Show answer
(a) sunken stomata and hairs trap a layer of still, moist air next to the stomata; wind does not remove the water vapour; reduces the water vapour concentration gradient so less diffusion out of the stomata
B1 still / humid air trapped; B1 protected from wind / air movement; B1 lower diffusion gradient of water vapour.
(b) less carbon dioxide can diffuse in, so the rate of photosynthesis is lower (slower growth)
B1.
Q18Adaptive features (xerophytes, hydrophytes) · Challenge · Paper 6 style · 6 marks
A student compares water loss from a cut shoot of oleander (a shrub that grows well in dry areas) with a cut shoot of sunflower. Each shoot is placed in a tube of water covered with oil and the whole apparatus is weighed. After 24 hours in the same conditions it is weighed again.plant | starting mass / g | mass after 24 h / goleander | 12.40 | 12.03sunflower | 10.80 | 8.64
(a)Calculate the percentage loss in mass for each plant. Give your answers to two significant figures.[2]
(b)Explain why percentage loss is used rather than the actual loss in mass.[1]
(c)State the purpose of the layer of oil.[1]
(d)Oleander leaves have a thick cuticle and stomata in hairy pits on the lower surface. Use this to explain the results.[2]
(b) the starting masses were different, so percentage allows a fair comparison
B1.
(c) prevents evaporation of water from the surface of the water in the tube
B1.
(d) thick cuticle reduces evaporation through the leaf surface; hairy pits trap moist air, lowering the water vapour gradient, so oleander loses far less water than sunflower
B1 cuticle; B1 hairy pits / trapped humid air / less diffusion of water vapour.
Q19Selective breeding · Core · Paper 2 style · 1 mark
(a)Which describes selective breeding?[1]
Show answer
(a) B Humans choose individuals with desirable features and breed them together.
Selective breeding is human choice of parents with desired features over many generations. A is natural selection; C is genetic modification.
Q20Selective breeding · Core · Paper 4 style · 4 marks
(a)Sahiwal cattle are a Pakistani breed known for good milk yield in hot weather. A farmer wants to increase the milk yield of his herd. Describe how he could do this by selective breeding.[4]
Show answer
(a) choose the cows with the highest milk yield; mate them with a bull whose mother/female relatives gave high yields; select the offspring with the highest yield and breed them; repeat for many generations
1 mark each for any four: select high-yield females; select suitable male (from high-yield line); breed them; select best offspring; repeat over many generations.
Q21Selective breeding · Standard · Paper 4 style · 3 marks
(a)Plant breeders want a wheat variety that has both high grain yield and resistance to rust disease. Explain why they must repeat the selection over many generations.[2]
(b)Suggest one advantage to farmers of growing disease-resistant wheat.[1]
Show answer
(a) the offspring vary and not all inherit both desired features; repeating selection increases the proportion of plants with the desired alleles until the variety breeds true
B1 offspring show variation / alleles not all passed on; B1 repeated selection makes desired features consistent in the population.
(b) less crop lost so higher yield / less money spent on fungicides / less pollution from chemicals
B1.
Q22Selective breeding · Standard · Paper 4 style · 3 marks
(a)State two disadvantages of selective breeding.[2]
(b)State one way in which selective breeding differs from natural selection.[1]
Show answer
(a) reduces genetic variation; increases risk of inherited disorders through inbreeding; whole population vulnerable to a new disease / environmental change; may cause health or welfare problems in animals
1 mark each for any two.
(b) humans choose which individuals breed (not the environment) / it is faster / the features chosen are useful to humans, not necessarily for survival
B1.
Q23Selective breeding · Challenge · Paper 4 style · 5 marks
A dairy farm has run a selective breeding programme for milk yield. The mean milk yield of cows in each generation is shown.generation | 0 | 1 | 2 | 3 | 4 | 5mean yield per cow per lactation / kg | 1400 | 1650 | 1900 | 2050 | 2120 | 2140
(a)Calculate the percentage increase in mean yield from generation 0 to generation 5. Give your answer to two significant figures.[2]
(b)Suggest two reasons why the yield increases very little after generation 3.[2]
(c)State one disadvantage of continuing to breed only from the highest-yielding cows.[1]
Show answer
(a) 53 %
M1 (2140 − 1400) ÷ 1400 × 100; A1 53 %.
(b) genetic variation in the herd has been reduced (most cows already have the high-yield alleles); yield is limited by environment, e.g. food, water, heat, health
B1 less genetic variation left to select from; B1 environmental limit / other factor limiting.
(c) reduced genetic variation so the herd is more likely to be affected by a new disease / inbreeding problems
B1.
Q24Selective breeding · Challenge · Paper 4 style · 5 marks
(a)Rice variety X has a strong basmati aroma but tall, weak stems that fall over in wind. Rice variety Y has short, strong stems and a high yield but no aroma. Describe how a plant breeder could use selective breeding to produce a short, high-yielding rice with a strong aroma, and explain why the process takes several years.[5]
Show answer
(a) cross-pollinate X and Y (transfer pollen, prevent self-pollination); grow the seeds; select offspring that have short stems, high yield and good aroma; breed (self or cross) these selected plants; repeat selection over many generations until all offspring show the desired features; takes years because each generation must grow to maturity and offspring vary, so many rounds of selection are needed
1 mark each for any five: cross X with Y; prevent self-pollination (remove anthers / cover flowers); grow offspring and select those with all desired features; breed from selected plants; repeat over many generations; offspring vary / not all inherit both features; each generation takes a season to grow.
Q25Natural selection, evolution & antibiotic resistance · Core · Paper 4 style · 3 marks
(a)Define evolution.[1]
(b)Define the process of adaptation.[2]
Show answer
(a) the change in adaptive features of a population over time as a result of natural selection
B1.
(b) the process, resulting from natural selection, by which populations become more suited to their environment over many generations
B1 result of natural selection; B1 population better suited over many generations.
Q26Natural selection, evolution & antibiotic resistance · Standard · Paper 2 style · 1 mark
(a)Which sequence describes natural selection?[1]
Show answer
(a) A variation → overproduction → competition → survival of the best adapted → reproduction → alleles passed on
Natural selection needs genetic variation, more offspring than can survive, competition, survival and reproduction of the better adapted, and passing on of their alleles. B describes inheritance of acquired characteristics, which is wrong.
Q27Natural selection, evolution & antibiotic resistance · Standard · Paper 4 style · 5 marks
(a)In parts of Sindh, typhoid bacteria resistant to most antibiotics have become common. Explain how a population of antibiotic-resistant bacteria develops.[5]
Show answer
(a) variation exists in the bacterial population; a random mutation gives some bacteria an allele for resistance; when the antibiotic is used, non-resistant bacteria are killed; resistant bacteria survive and reproduce; they pass on the resistance allele; over many generations the proportion of resistant bacteria increases
1 mark each for any five. Do not credit 'the antibiotic causes mutations' or 'bacteria become immune'.
Q28Natural selection, evolution & antibiotic resistance · Standard · Paper 4 style · 4 marks
(a)Insecticide sprays were used for many years in Lahore to control the mosquitoes that carry dengue fever. The sprays are now much less effective. Explain how this happened.[4]
Show answer
(a) some mosquitoes had (by mutation) an allele giving resistance; spraying killed non-resistant mosquitoes; resistant ones survived, reproduced and passed on the allele; over many generations most of the population became resistant
1 mark each for any four.
Q29Natural selection, evolution & antibiotic resistance · Challenge · Paper 4 style · 5 marks
(a)In one hospital, the percentage of samples of a bacterium that were resistant to a common antibiotic rose from 8 % in 2016 to 61 % in 2022. Calculate the percentage increase. Give your answer to two significant figures.[2]
(b)Suggest three ways in which the development of antibiotic resistance could be slowed.[3]
Show answer
(a) 660 %
M1 (61 − 8) ÷ 8 × 100 (= 662.5); A1 660 %. Do not accept 53 % (simple difference).
(b) use antibiotics only when necessary (not for viral infections); complete the full course; avoid routine use in farm animals; use the correct dose / prescription only; improve hygiene to reduce infections
1 mark each for any three.
Q30Natural selection, evolution & antibiotic resistance · Challenge · Paper 4 style · 4 marks
(a)Compare natural selection with selective breeding (artificial selection).[4]
Show answer
(a) in natural selection the environment 'selects' – organisms best adapted to the environment survive and reproduce; in selective breeding humans choose individuals with desired features to breed; natural selection is slow (many generations) while selective breeding is faster; both rely on genetic variation and the passing on of alleles to offspring; selective breeding features may not help survival in the wild
1 mark each for any four comparative points (a similarity counts).
Similar questions
Questions that test the same subtopic in different years, grouped so you can work on one skill at a time.
References only: find each question in its paper (official link where available, otherwise through your school).
