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 11 of 17

1. Q11 · Original practice · 1 mark
   Which organism occupies both the second and third trophic levels in the food web?
   Functioning ecosystems and succession
2. Q12 · Original practice · 1 mark
   Which conversion is carried out by nitrifying bacteria in the nitrogen cycle?
   Functioning ecosystems and succession
3. Q13 · Original practice · 1 mark
   Lichens begin colonising a newly exposed lava flow with no soil. This is an example of
   Functioning ecosystems and succession
4. Q14 · Original practice · 1 mark
   An orchid uses a tree branch for support. It gains better access to light, while measurements show no detectable effect on the tree. The interaction described is
   Functioning ecosystems and succession
5. Q15 · Original practice · 1 mark
   Two protist species use the same limiting food source. When cultured together, their populations follow the graph. Which conclusion is best supported?
   Functioning ecosystems and succession
6. Q16 · Original practice · 1 mark
   In a double-stranded DNA molecule, 28% of the bases are adenine. What percentage are cytosine?
   Genetics and heredity
7. Q17 · Original practice · 1 mark
   During DNA replication, which enzyme joins adjacent Okazaki fragments into a continuous strand?
   Genetics and heredity
8. Q18 · Original practice · 1 mark
   A diploid animal has 12 chromosomes in its somatic cells. At metaphase I of meiosis, one cell contains
   Genetics and heredity
9. Q19 · Original practice · 1 mark
   A DNA template is written $3^\prime\text{-TAC GGA CTT-}5^\prime$. The corresponding mRNA sequence, written $5^\prime$ to $3^\prime$, is
   Genetics and heredity
10. Q20 · Original practice · 1 mark
    A primary RNA transcript contains exon 1, intron 1, exon 2, intron 2 and exon 3, in that order. Which sequence remains after normal RNA splicing?
    Genetics and heredity
11. Q21 · Original practice · 1 mark
    A coding sequence changes the mRNA codon UAU to UAA. Use the supplied genetic code excerpt. The mutation is
    Genetics and heredity
12. Q22 · Original practice · 1 mark
    A woman with genotype $X^NX^n$ and a man with genotype $X^NY$ have a child. The allele $n$ causes an X-linked recessive trait. Assuming equal probabilities of male and female offspring, the probability that their child has the trait is
    Genetics and heredity
13. Q23 · Original practice · 1 mark
    For ABO blood groups, $I^A$ and $I^B$ are codominant and both dominate $i$. A parent with genotype $I^Ai$ and a parent with genotype $I^BI^B$ can produce children with blood groups
    Genetics and heredity
14. Q24 · Original practice · 1 mark
    The histogram shows variation in a trait within a large population raised under similar conditions. Which pattern of inheritance is most consistent with the distribution?
    Genetics and heredity
15. Q25 · Original practice · 1 mark
    A PCR starts with 3 double-stranded copies of a target region. Assuming ideal doubling in every cycle, how many double-stranded copies are present after 5 cycles?
    Genetics and heredity
16. Q26 · Original practice · 1 mark
    The gel shows DNA fragments from an unknown sample U and three reference samples. Which reference has the same banding pattern as U?
    Genetics and heredity
17. Q27 · Original practice · 1 mark
    A diploid population contains 36 AA, 48 Aa and 16 aa individuals. What is the frequency of allele A?
    Continuity of life on Earth
18. Q28 · Original practice · 1 mark
    A storm kills most beetles on an island, regardless of their colour. The survivors have a different colour-allele frequency from the original population. The most direct explanation is
    Continuity of life on Earth
19. Q29 · Original practice · 1 mark
    Which pair of species shares the most recent common ancestor in the cladogram?
    Continuity of life on Earth
20. Q30 · Original practice · 1 mark
    A shark and a dolphin independently evolved streamlined bodies while adapting to swimming. This similarity is an example of
    Continuity of life on Earth
21. Q31 · Original practice · 5 marks
    A floodplain contains reed beds, open water and woodland. Surveys record 32 bird species. Within one duck species, individuals carry different alleles for bill colour.
    Biodiversity and populations
22. Q32 · Original practice · 6 marks
    Equal-sized samples from two rock pools contain the animals shown. Use $SDI=1-\dfrac{\sum n(n-1)}{N(N-1)}$.
    Biodiversity and populations
23. Q33 · Original practice · 5 marks
    Researchers randomly locate eight 0.50 m² quadrats in a uniform 240 m² meadow. They count 3, 7, 4, 6, 5, 4, 8 and 3 orchid plants.
    Biodiversity and populations
24. Q34 · Original practice · 5 marks
    A saltmarsh reserve is 60% low marsh and 40% upper marsh. The habitats differ in flooding frequency and vegetation. Twenty quadrats can be sampled.
    Biodiversity and populations