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Cell division, variation and evolution: exam questions

6 questions, 18 marks. Write your answers on paper, then open each mark scheme.

Spec 3.28–3.39Questions and mark scheme (PDF)3 pages

Question 1

Which statement explains why brothers and sisters are not genetically identical?

  1. They are made by mitosis
  2. Fertilisation is random, so any sperm can fuse with any egg
  3. Each parent only passes on one chromosome
  4. They have different numbers of chromosomes
[1 mark]
Show mark scheme for question 1

Answer: B (1)

Question 2

State two uses of mitosis in a human.

[2 marks]
Show mark scheme for question 2
  • growth (1)
  • repair (1)
  • allow replacing damaged cells
  • ignore asexual reproduction

Question 3

Compare mitosis and meiosis, in terms of the number of cells produced, the number of chromosomes in each human cell, and genetic variation.

[4 marks]
Show mark scheme for question 3
  • mitosis produces two cells and meiosis produces four cells (1)
  • mitosis: each cell has 46 chromosomes / diploid; meiosis: 23 chromosomes / haploid (1)
  • mitosis produces cells that are genetically identical (1)
  • meiosis produces cells that are genetically different (1)

Question 4

Two identical twins were brought up in different places. One twin is 5 kg heavier than the other. (a) Suggest why the twins have the same eye colour. (1) (b) Suggest why the twins have different body masses. (2)

[3 marks]
Show mark scheme for question 4
  • they have the same alleles / genes / are genetically identical (1)
  • difference caused by the environment (1)
  • for example different diet / different amount of exercise (1)

Question 5

State what is meant by the term mutation.

[2 marks]
Show mark scheme for question 5
  • a (rare,) random change (1)
  • in genetic material / DNA that can be inherited (1)
  • allow change in the base sequence of DNA for the second marking point

Question 6

Some bacteria are resistant to an antibiotic. Explain how the number of resistant bacteria can increase in a population when the antibiotic is used, and explain why this makes infections difficult to control.

[6 marks]
Show mark scheme for question 6
LevelMarksWhat the answer does
35–6A clear, logical explanation that links variation, selection, survival, inheritance and the increase in the resistant population, and explains why infections become difficult to control.
23–4An explanation with some of the key steps in order, but with a missing link, or the effect on infection control is not explained.
11–2A few relevant points, such as that some bacteria survive the antibiotic. Little or no use of the idea of natural selection.

Indicative content

  • a mutation produces an allele that gives resistance to the antibiotic (variation)
  • the antibiotic kills non-resistant bacteria; the resistant bacteria survive (selection pressure)
  • the resistant bacteria reproduce, with less competition, and pass on the resistance allele
  • over time the proportion of resistant bacteria increases
  • the antibiotic no longer works against the infection, so it is difficult to control / can spread to other people
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