Biology questions and solutions
Browse original practice and official past-paper questions. Each question has its own link, with its source and worked solution.
385 questions · Page 15 of 17
- Q107 · Original practice · 1 markFunctioning ecosystems and successionIn waterlogged soil, nitrate is converted into nitrogen gas by microorganisms. Which nitrogen-cycle process is described?
- Q108 · Original practice · 1 markFunctioning ecosystems and successionAn undisturbed forest maintains broadly stable dominant vegetation over several decades, although individual trees die and are replaced. This observation is most consistent with
- Q109 · Original practice · 1 markFunctioning ecosystems and successionA fish population declines while water quality and habitat area remain similar. Catch records show that removal by fishing exceeded the production of new adult fish each year. Which human impact is most directly supported?
- Q110 · Original practice · 1 markGenetics and heredityTwo DNA samples contain the same percentages of A, T, G and C. Which additional information is required to determine whether a particular gene has the same base sequence in both samples?
- Q111 · Original practice · 1 markGenetics and heredityA UV-induced DNA mutation occurs in a skin cell. The cell divides and passes the mutation to its daughter skin cells. No gamete or gamete-forming cell carries the mutation. Which statement is supported?
- Q112 · Original practice · 1 markGenetics and heredityFor one chromosome pair, a meiosis produces four gametes: two contain both homologues and two contain neither. No other error occurs. The most likely error is
- Q113 · Original practice · 1 markGenetics and heredityA coding region gains one nucleotide and later loses one nucleotide downstream. Translation starts at the original start codon, and no new stop codon is introduced between the two changes. What happens to the reading frame downstream of both changes?
- Q114 · Original practice · 1 markGenetics and heredityAt one autosomal locus, allele F produces protein form F and allele S produces protein form S. FS heterozygotes produce both forms, each detectable separately. Which inheritance pattern is shown?
- Q115 · Original practice · 1 markContinuity of life on EarthAllele a produces a recessive phenotype only in aa individuals. Every aa individual fails to reproduce in one generation, but AA and Aa individuals reproduce. Why can a still be passed to offspring?
- Q116 · Original practice · 1 markContinuity of life on EarthA source population contains 50 AA and 50 aa individuals. Two Aa offspring from this population found a new island population. What is true of A frequency at this locus in the source and founder populations?
- Q117 · Original practice · 1 markContinuity of life on EarthThe phylogram shows three species. Horizontal lengths represent sequence differences; vertical spacing has no scale. What is the total sequence difference along the path joining species A and B?
- Q118 · Original practice · 1 markContinuity of life on EarthA resistance allele is detected in stored DNA from a population sampled before a particular pesticide was first used there. After pesticide use begins, individuals carrying the allele leave more offspring and its frequency increases. Which explanation is best supported?
- Q119 · Original practice · 6 marksBiodiversity and populationsEqual-sized invertebrate samples are taken from two ponds using the same technique. Use . The species counts are shown.
- Q120 · Original practice · 5 marksBiodiversity and populationsTwo teams independently sample the same uniform meadow at random positions. Team S uses ten 0.25 m² quadrats and counts 20 plants in total. Team L uses ten 1.00 m² quadrats and counts 80 plants in total. The meadow area is 600 m².
- Q121 · Original practice · 5 marksBiodiversity and populationsA 5000 m² reserve contains dry habitat covering 70% of its area and wet habitat covering 30%. Equal numbers of random quadrats are placed in the two strata. Their mean plant densities are 2 plants m⁻² in dry habitat and 12 plants m⁻² in wet habitat. Treat these as representative density estimates.
- Q122 · Original practice · 5 marksBiodiversity and populationsA capture–recapture estimate uses M = 50, n = 80 and m = 16. An independent complete census later shows that the population was 500 during both capture sessions. All marks remained visible. Marked animals had been released beside baited traps and returned to those traps more often than unmarked animals.
- Q123 · Original practice · 6 marksBiodiversity and populationsThe curves show cumulative plant-species counts from randomly located equal-sized quadrats in habitats X and Y. Within each habitat, no previously recorded species is removed from the cumulative total.
- Q124 · Original practice · 5 marksBiodiversity and populationsSeedlings of one species are grown in a controlled experiment with two maintained soil-moisture levels and two light treatments. Each treatment starts with 30 seedlings and is repeated six times. Other conditions are held similar. The table gives mean survivors after four weeks.
- Q125 · Original practice · 4 marksBiodiversity and populationsBefore logging, the tallest vegetation stratum consists of 36 m trees with 55% foliage projective cover. After logging, the remaining tallest trees are 8 m high with 40% cover. A 3 m shrub layer has 85% cover. Use the supplied Specht excerpt; all cover values lie away from boundaries.
- Q126 · Original practice · 6 marksBiodiversity and populationsA closed population is monitored in a habitat with limited food. Extra food becomes continuously available on day 10 and remains available. The graph shows the response; no other condition is deliberately changed.
- Q127 · Original practice · 5 marksFunctioning ecosystems and successionA grassland has annual producer GPP of 25 000 kJ m⁻² and producer respiration of 9000 kJ m⁻². Two consumer groups feed directly on separate portions of producer material: grazers on living leaves and detritivores on dead leaves. They do not feed on one another. Their annual new biomass contains 700 and 1300 kJ m⁻² respectively.
- Q128 · Original practice · 5 marksFunctioning ecosystems and successionProducer productivity is measured over equal periods in two seasons. Grazers feed on these producers; other limitations on grazers are not measured.
- Q129 · Original practice · 6 marksFunctioning ecosystems and successionA harmless nitrogen-isotope tracer is initially supplied as nitrate to plants. Later it is detected successively in plant proteins, grazer proteins, dead organic matter, ammonium and nitrate. The isotope identifies the nitrogen atoms; it does not alter their chemical behaviour.
- Q130 · Original practice · 5 marksFunctioning ecosystems and successionArrows in the food web point from food to consumer. The feeding links shown are the only links considered in this model.