Studyledge

Reproduction: Question 1

Syllabus 16.1, 16.2

Multiple choice Core 1 mark

A rose bush is home to a large colony of aphids (small sap-feeding insects). Throughout the summer, every aphid in the colony is female. Each female produces many new aphids without mating with a male: every new aphid develops from a single egg cell inside her body, and each one is genetically identical to her. As autumn approaches, some females instead produce egg cells that must first be fertilised by a male aphid before they can develop into the next generation.

Which statement correctly compares these two ways in which the aphids produce new individuals?

Choose an answer to check it, then compare with the worked solution below.
Show worked solution Hide worked solution

Worked solution

Step 1: Recall the defining features of asexual and sexual reproduction

Asexual reproduction involves a single parent and no fusion of gametes, so the offspring are genetically identical to that one parent. Sexual reproduction involves the fusion of the nuclei of two gametes, one from each of two parents, so the offspring are genetically different from both parents (and from each other).

Step 2: Apply this to the summer aphids

In summer, each female aphid produces new aphids on her own, without mating. No male gamete is involved and no fusion of nuclei takes place, the egg cell inside her develops into a new aphid by itself. Because there is only one parent and no gamete fusion, this is asexual reproduction, and every offspring produced this way is genetically identical to its mother.

Step 3: Apply this to the autumn aphids

In autumn, the egg cells produced by some females must be fertilised by a male aphid before they can develop. This fertilisation is the fusion of a male gamete’s nucleus with the egg cell’s nucleus, two parents contribute genetic material. Because gametes from two parents fuse, this is sexual reproduction, and the resulting offspring are genetically variable, not identical to either parent.

Why the other options are wrong

  • B: reverses the two processes. Producing an egg cell is not, by itself, evidence of sexual reproduction; it is the fusion of that egg cell with a male gamete that makes a process sexual. The unmated summer process is asexual, and the mated autumn process is sexual.
  • C: wrongly assumes that because only females are directly “producing” the egg cells, both processes must be asexual; it ignores that the autumn egg cells are fertilised by a male gamete, which makes that process sexual.
  • D: wrongly assumes an egg cell can only ever result from sexual reproduction; an unfertilised egg cell that develops on its own, as in the summer aphids, is still part of an asexual process.

Final answer

The summer method (no mating, genetically identical offspring) is asexual reproduction; the autumn method (fertilisation by a male aphid, genetically variable offspring) is sexual reproduction, option A.