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 1 of 17

1. Q1 · 2025 QCAA · Paper 1 · 1 mark
   QUESTION 1 Which base pairs with adenine during DNA replication? (A) uracil (B) guanine (C) thymine (D) cytosine
   Genetics and heredity
2. Q2 · 2025 QCAA · Paper 1 · 1 mark
   QUESTION 2 The diagram shows energy flow through an ecosystem in kJ m−2 year−1. Shaded boxes represent gross productivity. Respiration and heat 50 000 7800 Primary consumers Sunlight Producers 7 200 000 87 000 22 600 5060 Decomposers Calculate the percentage of solar energy available to primary consumers. (A) 0.1% (B) 0.2% (C) 0.4% (D) 0.5%
   Functioning ecosystems and succession
3. Q3 · 2025 QCAA · Paper 1 · 1 mark
   QUESTION 3 As a population approaches its carrying capacity, the population growth rate will (A) increase due to intraspecific competition. (B) increase due to interspecific competition. (C) decrease due to intraspecific competition. (D) decrease due to interspecific competition.
   Biodiversity and populations
4. Q4 · 2025 QCAA · Paper 1 · 1 mark
   QUESTION 4 What is the role of tRNA in protein synthesis? (A) acting as a template strand for mRNA (B) matching amino acids to mRNA codons (C) transporting mRNA from the nucleus to the ribosome (D) providing a copy of genetic instructions for the ribosome
   Genetics and heredity
5. Q5 · 2025 QCAA · Paper 1 · 1 mark
   QUESTION 5 Which option describes the contents of a human cell at metaphase I of meiosis? Number of chromosomes Number of copies of each gene (A) 23 1 (B) 23 2 (C) 46 2 (D) 46 4
   Genetics and heredity
6. Q6 · 2025 QCAA · Paper 1 · 1 mark
   QUESTION 6 A student investigating the impact of a selection pressure on a population collected the data shown. Genotype BB Bb bb Number of individuals 128 220 85 Calculate the frequency of the recessive allele in the population. (A) 10% (B) 20% (C) 32% (D) 45%
   Continuity of life on Earth
7. Q7 · 2025 QCAA · Paper 1 · 1 mark
   QUESTION 7 Which process is involved in both carbon and water cycling? (A) respiration (B) evaporation (C) transpiration (D) precipitation
   Functioning ecosystems and succession
8. Q8 · 2025 QCAA · Paper 1 · 1 mark
   QUESTION 8 Speciation is more likely to occur between two populations when (A) gene flow is low and selection pressures are similar. (B) gene flow is high and selection pressures are similar. (C) gene flow is low and selection pressures are different. (D) gene flow is high and selection pressures are different.
   Continuity of life on Earth
9. Q9 · 2025 QCAA · Paper 1 · 1 mark
   QUESTION 9 Which term describes large, geographically distinct areas of Earth’s surface with common climates, geology, landforms and communities? (A) niches (B) ecoregions (C) environments (D) microhabitats
   Biodiversity and populations
10. Q10 · 2025 QCAA · Paper 1 · 1 mark
    QUESTION 10 In humans, sex-linked recessive traits are more common in (A) males, because they have a Y chromosome. (B) females, because they have two X chromosomes. (C) males, because they have only one X chromosome. (D) females, because they do not have a Y chromosome.
    Genetics and heredity
11. Q11 · 2025 QCAA · Paper 1 · 1 mark
    QUESTION 11 A student surveying a forest community collected the data shown. Species Number of individuals W 220 X 123 Y 62 Z 145 Calculate the relative abundance of species W. (A) 0.22 (B) 0.25 (C) 0.40 (D) 0.67
    Biodiversity and populations
12. Q12 · 2025 QCAA · Paper 1 · 1 mark
    QUESTION 12 An experiment was conducted to determine how the concentration of calcium chloride (CaCl2) affects the transformation efficiency of plasmids. Error bars show standard error. 6 Transformation efficiency (104 cfu/μg) 5 4 3 2 1 0 0.3 0.0 0.1 0.2 Concentration of CaCl2 (M) Which concentration had the greatest variation in transformation efficiency? (…
    Genetics and heredity
13. Q13 · 2025 QCAA · Paper 1 · 1 mark
    QUESTION 13 The cladogram shows relationships for species P, Q, R, S and T. P Q R S T hair amniotic egg four limbs backbone What inference can be drawn? (A) Species Q, R and S form a clade. (B) Species P and R are more closely related than species P and T. (C) The most recent common ancestor of species R and T had four limbs. (D) Species Q and R have a m…
    Continuity of life on Earth
14. Q14 · 2025 QCAA · Paper 1 · 1 mark
    QUESTION 14 Which species concept is based on common ancestry? (A) biological (B) ecological (C) phylogenetic (D) morphological
    Biodiversity and populations
15. Q15 · 2025 QCAA · Paper 1 · 1 mark
    QUESTION 15 Which technique identifies the order of bases in DNA? (A) DNA profiling (B) DNA sequencing (C) gel electrophoresis (D) polymerase chain reaction
    Genetics and heredity
16. Q16 · 2025 QCAA · Paper 1 · 1 mark
    QUESTION 16 The table shows haploid (n) and diploid (2n) chromosome numbers for different matings. Mating Female Male I n = 32 2n = 62 II 2n = 62 n = 31 III n = 31 2n = 62 IV 2n = 64 n = 32 Predict which mating would produce an interspecific hybrid. (A) I (B) II (C) III (D) IV
    Genetics and heredity
17. Q17 · 2025 QCAA · Paper 1 · 1 mark
    QUESTION 17 Which mode of evolution involves the development of complementary characteristics in two species experiencing a close and long-term interaction? (A) coevolution (B) parallel evolution (C) divergent evolution (D) convergent evolution
    Continuity of life on Earth
18. Q18 · 2025 QCAA · Paper 1 · 1 mark
    QUESTION 18 Which mutation is likely to have the greatest effect on the viability of an embryo? (A) a point mutation in a HOX gene (B) a point mutation in the SRY gene (C) a frameshift mutation in a HOX gene (D) a frameshift mutation in the SRY gene
    Genetics and heredity
19. Q19 · 2025 QCAA · Paper 1 · 1 mark
    QUESTION 19 Which process involves the random alignment and separation of homologous chromosomes to form unique combinations of maternal and paternal chromosomes in gametes? (A) cytokinesis (B) crossing over (C) recombination (D) independent assortment
    Genetics and heredity
20. Q20 · 2025 QCAA · Paper 1 · 1 mark
    QUESTION 20 The graph shows the relative impact of habitat destruction, overexploitation, pollution and other human activities on four taxonomic groups. Reptiles and amphibians Land mammals Birds Fish 0 10 20 30 40 50 60 70 80 90 100 Relative impact (%) Key Habitat destruction Overexploitation Pollution Other Which activity has the greatest impact on terrest…
    Functioning ecosystems and succession
21. Q21 · 2025 QCAA · Paper 1 · 4 marks
    QUESTION 21  (4 marks) a) Describe two key features of the Linnaean system of biological classification. [2 marks] b) Explain, using an example, how the Linnaean system allows researchers to infer similarities between species. [2 marks]
    Biodiversity and populations
22. Q22 · 2025 QCAA · Paper 1 · 5 marks
    QUESTION 22  (5 marks) a) Compare the role of pioneer species in primary and secondary succession. [3 marks] Similarity:

    Difference:

    Significance:

    b) Describe two ways climax communities differ from pioneer communities. [2 marks]
    Functioning ecosystems and succession
23. Q23 · 2025 QCAA · Paper 1 · 6 marks
    QUESTION 23  (6 marks) a) Identify two enzymes involved in DNA replication and describe their functions. [4 marks] Enzyme 1: Function:

    Enzyme 2: Function:

    b) Explain how synthesis of the leading strand is different from the lagging strand. [2 marks]
    Genetics and heredity
24. Q24 · 2025 QCAA · Paper 1 · 2 marks
    QUESTION 24  (2 marks) Describe the structure of plasmids and their role in making recombinant DNA.
    Genetics and heredity