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Selective breeding and tissue culture: exam questions

6 questions, 15 marks. Write your answers on paper, then open each mark scheme.

Spec 4.8–4.9BQuestions and mark scheme (PDF)3 pages

Question 1

Which is a possible disadvantage of selective breeding?

  1. It increases genetic variation.
  2. It reduces genetic variation.
  3. It only takes one generation.
  4. It involves inserting genes from other species.
[1 mark]
Show mark scheme for question 1

Answer: B (1)

Question 2

Describe how a farmer could use selective breeding to produce cattle that give more milk.

[4 marks]
Show mark scheme for question 2
  • select a bull and cows that produce a lot of milk / with high milk yield (1)
  • breed them together (1)
  • select offspring that produce the most milk and breed them (1)
  • repeat over many generations (1)

Question 3

In a plant, resistance to a disease is controlled by a dominant allele R. Susceptibility is controlled by the recessive allele r. Two plants with the genotype Rr are crossed. Use a genetic diagram to find the probability that an offspring is susceptible.

[3 marks]
Show mark scheme for question 3
  • gametes R and r from each parent (1)
  • offspring RR, Rr, Rr, rr (1)
  • probability of rr = 1/4 or 25% (1)

Question 4

Triple only (what this means)Triple only: only in Triple Biology. Combined Science students can skip it. What the labels mean

Describe how tissue culture can be used to produce new plants.

[3 marks]
Show mark scheme for question 4
  • take small pieces of tissue / cells from the parent plant (1)
  • use aseptic technique / sterile conditions to prevent contamination (1)
  • grow on a nutrient medium (agar) with nutrients and growth hormones (1)
  • cells divide to form new plants that are identical to the parent (1)
  • Max 3

Question 5

Triple only (what this means)Triple only: only in Triple Biology. Combined Science students can skip it. What the labels mean

Give two advantages of using tissue culture in plant breeding programmes.

[2 marks]
Show mark scheme for question 5
  • many identical plants produced quickly (1)
  • from a small amount of tissue (1)
  • desirable characteristics are kept / plants are genetically identical (1)
  • can be done all year / in a small space (1)
  • rare / endangered plants can be reproduced (1)
  • Max 2

Question 6

Triple only (what this means)Triple only: only in Triple Biology. Combined Science students can skip it. What the labels mean

Explain how tissue culture is useful in medical research.

[2 marks]
Show mark scheme for question 6
  • large numbers of identical cells can be grown (1)
  • so new drugs can be tested on them / disease can be studied, with reliable results (1)
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