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 14 of 17

1. Q83 · Original practice · 6 marks
   A biologist genotypes every adult in a small diploid frog population. There are 25 AA, 50 Aa and 25 aa frogs in year 1. In year 2 there are 40 AA, 40 Aa and 20 aa frogs.
   Continuity of life on Earth
2. Q84 · Original practice · 5 marks
   Three events occur in separate beetle populations: P gains a new allele after a DNA-copying error; Q receives breeding immigrants carrying an allele rare in the local population; R is founded by five beetles that happen to lack an allele common in their source population.
   Continuity of life on Earth
3. Q85 · Original practice · 6 marks
   The solid curve is the original distribution of a heritable body-length trait. X and Y are distributions after selection in two independent populations. The same scale is used for all curves.
   Continuity of life on Earth
4. Q86 · Original practice · 7 marks
   A fire kills individuals without regard to genotype. A diploid lizard population is reduced from 200 to 20 individuals. The table records one locus; separate genomic data also show that several rare alleles were lost at other loci.
   Continuity of life on Earth
5. Q87 · Original practice · 6 marks
   Consider three hypothetical plant populations: P is divided by a new river barrier; Q contains groups in the same field that flower in different months; R occupies adjacent ends of a continuous moisture gradient and neighbouring groups mate more often than distant groups.
   Continuity of life on Earth
6. Q88 · Original practice · 6 marks
   The table describes four evolutionary patterns. Treat the stated lineage relationships as evidence.
   Continuity of life on Earth
7. Q89 · Original practice · 5 marks
   A conserved sequence accumulates substitutions at an average rate $r=0.40$ sites per million years in each of two lineages. The lineages differ at 12 sites. Assume a constant rate, independent accumulation, and no repeated changes at the same site. Use $d=2rt$.
   Continuity of life on Earth
8. Q90 · Original practice · 6 marks
   The table shows an aligned 12-base conserved sequence from four hypothetical species. D is the outgroup. Assume fewer differences in this sequence indicate closer relatedness for this question.
   Continuity of life on Earth
9. Q91 · Original practice · 9 marks
   A storm changes a pond community. Equal-sized macroinvertebrate samples and annual producer/grazer energy data are shown. Use $SDI=1-\dfrac{\sum n(n-1)}{N(N-1)}$.
   Biodiversity and populations
10. Q92 · Original practice · 9 marks
    A researcher marks 30 frogs and releases them. In a later capture of 45 frogs, 9 are marked. These 45 frogs comprise 9 AA, 24 Aa and 12 aa individuals at one diploid locus. Assume a closed, well-mixed population and a genotype-representative sample. After both captures, 20 AA frogs immigrate; no other population changes occur.
    Biodiversity and populations
11. Q93 · Original practice · 9 marks
    A grassland fire leaves soil and a seed bank intact. As shrubs establish, light reaching the ground decreases. In one diploid annual herb, allele S increases shade tolerance. The table shows complete genotype counts before the fire and after several generations of succession. Assume no immigration or new mutations during this period.
    Functioning ecosystems and succession
12. Q94 · Original practice · 8 marks
    A hypothetical reserve contains dingoes, browsing wallabies and young trees. After dingo numbers recover, wallaby abundance falls and tree growth increases. The carbon table includes all photosynthetic uptake and biotic respiratory return for the measured plots; assume other carbon exchanges are negligible.
    Functioning ecosystems and succession
13. Q95 · Original practice · 8 marks
    In a hypothetical beetle, functional allele G is dominant and produces a green-pigment enzyme. Allele g changes the mRNA codon CAA (glutamine) to UAA (stop), producing a non-functional enzyme. Both parents are green and have genotype Gg. A 600 bp DNA test fragment is cut into 400 bp and 200 bp fragments for G; g lacks the restriction site and remains 600 bp.…
    Genetics and heredity
14. Q96 · Original practice · 9 marks
    Identical starting seed mixtures are placed in wet and dry microhabitats. At the end, plant counts are shown. In species A, gene X has the same DNA sequence in both microhabitats, but dry-site cells have more transcription-factor binding at its promoter and ten times more X mRNA. Use $SDI=1-\dfrac{\sum n(n-1)}{N(N-1)}$.
    Genetics and heredity
15. Q97 · Original practice · 9 marks
    A diploid beetle population is exposed to an insecticide. Survival data are shown. After exposure, 12 aa adults immigrate. No further births or deaths occur before the next count.
    Continuity of life on Earth
16. Q98 · Original practice · 8 marks
    Before a wildlife corridor opens, researchers mark 54 frogs in an isolated wetland. A second capture contains 75 frogs, 18 marked. Assume Lincoln-index conditions are met. A separate representative genetic sample estimates A frequency as 0.20 at one diploid locus. After the capture study finishes, the corridor allows 15 AA frogs to join the breeding populati…
    Biodiversity and populations
17. Q99 · Original practice · 9 marks
    The matrix gives pairwise differences in one conserved DNA sequence. D is an outgroup. Assume fewer differences indicate closer relatedness. For A and B, use the molecular-clock model $d=2rt$, with $r=0.25$ differences per million years in each lineage. For this question only, assume sequence divergence tracks population divergence exactly. A geographic barr…
    Continuity of life on Earth
18. Q100 · Original practice · 10 marks
    An investigator wants bacteria to make a eukaryotic luminescent protein. Its complete RNA coding region has exons of 150 and 240 nucleotides, including the start codon and one final stop codon, separated in the original gene by a 100-nucleotide intron. The intron contains an early stop and the host cannot splice it. Candidate plasmids have a 1810 bp vector b…
    Genetics and heredity
19. Q101 · Original practice · 1 mark
    Two beetle groups live in the same forest and have almost identical appearances. Each group breeds successfully within itself, but crosses between the groups consistently produce sterile offspring. Which conclusion is most consistent with the biological species concept?
    Biodiversity and populations
20. Q102 · Original practice · 1 mark
    In a capture–recapture study, marks are retained and the population is closed. Marked animals become less likely than unmarked animals to enter a trap. With first-capture number M and second-capture number n unchanged, the Lincoln-index estimate is most likely to
    Biodiversity and populations
21. Q103 · Original practice · 1 mark
    Two samples each contain three equally abundant species. Sample P contains 5 individuals of each species; sample Q contains 30 of each. Use $SDI=1-\frac{\sum n(n-1)}{N(N-1)}$. Which statement is correct?
    Biodiversity and populations
22. Q104 · Original practice · 1 mark
    A reserve contains 75% woodland and 25% wetland. An investigator can place 24 quadrats and wants proportional stratified random sampling. Which plan meets this requirement?
    Biodiversity and populations
23. Q105 · Original practice · 1 mark
    A census interval begins with 280 birds and ends with 310. During the interval there are 44 deaths, 12 immigrants and 18 emigrants. How many births occurred?
    Biodiversity and populations
24. Q106 · Original practice · 1 mark
    A grazer consumes food containing 1200 kJ. During the same interval it egests 500 kJ and releases 450 kJ through respiration. These are the only losses in the complete energy budget. How much energy is stored in new grazer biomass?
    Functioning ecosystems and succession