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 13 of 17

1. Q59 · Original practice · 5 marks
   Two equal-area farm plots are surveyed using the same method. Plot M is a monoculture; plot D contains several crop species. The table summarises their arthropod communities.
   Functioning ecosystems and succession
2. Q60 · Original practice · 6 marks
   Large fish are removed from the food web. Assume feeding links remain unchanged and food, rather than habitat space, limits the grazing snails and insect larvae.
   Functioning ecosystems and succession
3. Q61 · Original practice · 6 marks
   The diagram represents a short fragment of double-stranded DNA. Numbers 1–4 indicate structures or bonds.
   Genetics and heredity
4. Q62 · Original practice · 5 marks
   One strand of a double-stranded DNA fragment is $5^\prime\text{-AAGTCCGA-}3^\prime$.
   Genetics and heredity
5. Q63 · Original practice · 5 marks
   The replication fork moves to the right. Template-strand ends are labelled. Arrows on new DNA indicate synthesis direction.
   Genetics and heredity
6. Q64 · Original practice · 6 marks
   A diploid species has 2n = 4. The diagram shows a cell before the first meiotic division (A) and one daughter cell after that division (B).
   Genetics and heredity
7. Q65 · Original practice · 5 marks
   Two loci are linked on a homologous chromosome pair. The alleles are arranged $AB$ on one homologue and $ab$ on the other. A crossover occurs between the loci in two non-sister chromatids.
   Genetics and heredity
8. Q66 · Original practice · 6 marks
   Letters represent chromosome segments, not individual nucleotides. Normal chromosomes have orders ABCDEF and PQRSTU. Four independent changes are shown.
   Genetics and heredity
9. Q67 · Original practice · 7 marks
   The schematic karyotype shows a human cell. Chromosomes are arranged by numbered homologous groups. The sex chromosomes are labelled.
   Genetics and heredity
10. Q68 · Original practice · 5 marks
    Compare spermatogenesis and oogenesis in humans.
    Genetics and heredity
11. Q69 · Original practice · 6 marks
    A short coding region on a DNA template is $3^\prime\text{-TAC AAA GGC ACT-}5^\prime$. The genetic code excerpt is provided.
    Genetics and heredity
12. Q70 · Original practice · 6 marks
    A eukaryotic primary RNA transcript contains three exons of 90, 120 and 150 nucleotides, separated by two introns of 80 and 100 nucleotides. Ignore the 5′ cap and poly-A tail in length calculations.
    Genetics and heredity
13. Q71 · Original practice · 5 marks
    An mRNA normally contains the codon GAA. Three independent base substitutions produce GAG, GUA and UAA. Use the code excerpt.
    Genetics and heredity
14. Q72 · Original practice · 5 marks
    A translated mRNA segment begins $5^\prime\text{-AUG AAA GGC UCU UAA-}3^\prime$. Mutant P loses the fourth nucleotide; mutant Q loses nucleotides 4–6. Read from the original start codon.
    Genetics and heredity
15. Q73 · Original practice · 5 marks
    Two cells from the same organism have the same DNA sequence. Measurements at one gene are shown. Chemical tags associated with compact chromatin are more abundant in cell A.
    Genetics and heredity
16. Q74 · Original practice · 5 marks
    A muscle cell and a nerve cell contain the same genome but produce different sets of proteins.
    Genetics and heredity
17. Q75 · Original practice · 5 marks
    The diagram shows expression of a hypothetical HOX gene in six segments of an embryo. In this species, the gene helps establish segment identity. Shading represents expression, not a DNA-sequence difference.
    Genetics and heredity
18. Q76 · Original practice · 6 marks
    The pedigree shows a fully penetrant trait with no new mutations. Choose among autosomal dominant, autosomal recessive and X-linked recessive inheritance. Use A for the normal dominant allele if a recessive model applies.
    Genetics and heredity
19. Q77 · Original practice · 5 marks
    The pedigree traces a known X-linked recessive trait. Assume complete penetrance and no new mutations. Use $X^N$ for the normal allele and $X^n$ for the trait allele.
    Genetics and heredity
20. Q78 · Original practice · 6 marks
    A person with blood group A and a person with blood group B have a child with blood group O. For ABO inheritance, $I^A$ and $I^B$ are codominant and both dominate $i$.
    Genetics and heredity
21. Q79 · Original practice · 6 marks
    In a hypothetical flower, three independently assorting loci contribute additively to pigment. Each upper-case allele adds one pigment unit. An $AABBCC$ plant is crossed with an $aabbcc$ plant. Their offspring are then crossed with one another; the histogram shows 256 offspring of this second cross.
    Genetics and heredity
22. Q80 · Original practice · 6 marks
    A bacterial plasmid has a replication origin, an antibiotic-resistance marker and one unique restriction site. An investigator wants to insert gene X at that site.
    Genetics and heredity
23. Q81 · Original practice · 6 marks
    PCR begins with 5 double-stranded copies of a target region. Assume ideal doubling each cycle until the stated comparison.
    Genetics and heredity
24. Q82 · Original practice · 6 marks
    The gel shows DNA profiles at two inherited loci. Each individual has two distinct bands at each locus; one allele at each locus is inherited from each parent. Assume no new mutations and that the child’s mother is M. A, B and C are possible fathers.
    Genetics and heredity