1. 1
   A strawberry grower produces new plants in two ways: by allowing runners (stolons) to grow roots and become new plants, and by growing new plants from seeds produced after pollination and fertilisation. In one growing season, the grower notices that all the runner-produced plants have identical fruit size and colour, whereas the seed-produced plants show a wide range of fruit sizes and colours.

   (a)

   Which type of cell division produces the new runner plants?

   [1 mark]

   • AMitosis
   • BMeiosis
   • CFertilisation
   • DTranslation

   (b)

   Which statement best explains why the runner plants show no variation in fruit size or colour?

   [1 mark]

   • ATheir DNA mutates in the same way each time a runner forms
   • BThey are produced by meiosis, which halves the chromosome number
   • CThey inherit DNA from two parent plants
   • DThey are produced by mitosis, which produces genetically identical offspring

   (c)

   State one advantage and one disadvantage of asexual reproduction for the strawberry grower, using information from the scenario.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Aphids are small insects that feed on plant sap. In summer, when host plants are abundant and temperatures are warm, aphid populations reproduce asexually, with each female producing genetically identical offspring without mating. In autumn, as conditions become colder and food becomes scarcer, some aphids switch to sexual reproduction, producing eggs that overwinter and hatch as genetically varied offspring in spring.

   (a)

   Which of the following is an advantage of asexual reproduction for the aphids in summer?

   [1 mark]

   • AOffspring inherit alleles from two parents
   • BIncreased genetic variation among offspring
   • CNo need to find a mate, allowing rapid population increase
   • DOffspring are produced by meiosis

   (b)

   Why is sexual reproduction advantageous for the aphids as conditions become less favourable in autumn?

   [1 mark]

   • AIt removes the need for the aphids to find a mate
   • BIt produces genetically varied offspring, increasing the chance that some survive the changing conditions
   • CIt always produces more offspring than asexual reproduction
   • DIt prevents any mutations from occurring in the offspring

   (c)

   Explain one disadvantage of asexual reproduction that sexual reproduction overcomes, using the aphid example.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A liver cell in an animal contains 24 chromosomes (12 pairs) in its nucleus. A biologist is studying a testis cell from the same animal, which also starts with 24 chromosomes, as it divides by meiosis to form sperm cells.

   (a)

   Describe what happens to the chromosome number when the testis cell divides by meiosis to form sperm cells, and state how many sperm cells are produced from each testis cell.

   [3 marks]

   (b)

   Explain why the sperm cells produced by meiosis are genetically different from each other and from the parent testis cell, and why this genetic difference is important for the species.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A species of freshwater snail can reproduce both asexually (a single snail producing offspring without mating or gametes) and sexually (by mating with another snail). In a stable pond with few predators and a constant food supply, most snails reproduce asexually. When a new species of fish that eats snails is introduced to the pond, a much higher proportion of snails begin reproducing sexually.

   (a)

   Discuss the advantages and disadvantages of asexual reproduction for the snails living in the stable pond, before the new fish species was introduced.

   [6 marks]

   (b)

   Explain why a higher proportion of snails reproduce sexually after the new predatory fish is introduced to the pond, and evaluate why this response gives the snail population a survival advantage.

   [6 marks]

   Total for question 4: 12 marks

End of questions