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IGCSE · Practice questions · Sexual reproduction

Mixing genes from two parents.

Six original Cambridge-style questions on sexual reproduction: definitions, fertilisation, chromosome numbers in gametes and zygotes, and (Extended) a balanced comparison with asexual reproduction for wild species and crops.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Keep these straight

Fusion of nuclei, variation.

01
Recall
[3 marks]

Describe sexual reproduction.

  • The nuclei of two gametes (sex cells) fuse. ✓
  • This forms a zygote. ✓
  • The offspring produced are genetically different from each other (and from the parents). ✓
02
Recall
[1 marks]

Define fertilisation.

  • The fusion of the nuclei of two gametes (a male and a female gamete). ✓
03
Calculation
[2 marks]

Extended. A fruit fly has 8 chromosomes in each body cell. State the number of chromosomes in (a) a sperm cell and (b) a zygote. Use the terms haploid and diploid.

  • (a) 4: the sperm nucleus is haploid, with one set of chromosomes. ✓
  • (b) 8: the zygote nucleus is diploid, with two sets (one from each parent). ✓
04
Explain
[2 marks]

Extended. Explain why gametes must be haploid.

  • At fertilisation two gamete nuclei fuse, so their chromosome numbers add together. ✓
  • If gametes are haploid the zygote is diploid, so the chromosome number stays the same in every generation (it does not double). ✓
05
Explain
[4 marks]

Extended. Discuss the advantages and disadvantages of sexual reproduction to a species of wild plant.

  • Advantage: offspring show variation, so some may survive a new disease or a change in the environment. ✓
  • Advantage: the species can adapt by natural selection; seeds spread offspring away from the parent, reducing competition. ✓
  • Disadvantage: it needs two parents and often pollinators, so an isolated plant may not reproduce. ✓
  • Disadvantage: it is slower and uses more energy (flowers, nectar, many pollen grains). ✓
06
Analysis
[3 marks]

Extended. A plant breeder wants a new wheat variety that resists a fungal disease, then wants to grow large fields of it. Suggest why the breeder uses sexual reproduction for the first stage, and why the uniformity of the final crop is both useful and risky.

  • Sexual reproduction (crossing two parent plants) produces variation, so new combinations such as disease resistance can be found and selected. ✓
  • A uniform crop gives predictable yield and ripens at the same time. ✓
  • But if a new form of the fungus appears, all plants may be equally affected, so the whole crop could be lost. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.