Selective breeding and chemical fertilisers are two methods used to increase food supply. Describe how each method increases the yield of a crop.

Cambridge International IGCSE Biology (0610) — 20.1 Food supply · Describe · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Selective breeding: farmers choose plants that show desirable traits such as high yield and breed them. The offspring inherit these traits, producing more high‑yielding plants.
Chemical fertilisers: they add mineral salts (nitrogen, phosphorus, potassium) to the soil, increasing the nutrients available to plants. With more nutrients, plants grow larger and produce more fruit, raising the crop yield.

Examiner tips

  • Use the word ‘selective breeding’ and ‘chemical fertilisers’ explicitly. Show the cause–effect chain: choice → inheritance → higher yield; fertiliser → more nutrients → larger plants → more fruit.
  • Include key nutrients (N, P, K) to demonstrate knowledge of fertiliser composition.

Common mistakes

  • Confusing selective breeding with random mutation. Forgetting to mention that offspring inherit the selected traits. Describing fertilisers as ‘food for plants’ instead of mineral salts.

Mark scheme (4 marks)

  1. Selective breeding — organisms with desirable characteristics (e.g. high yield) are chosen to breed
  2. Selective breeding — offspring inherit desirable characteristics / high yield, producing a large number of high-yielding plants
  3. Chemical fertilisers provide / increase mineral salts / nutrients in the soil
  4. Chemical fertilisers allow plants to grow larger / produce more fruit, increasing yield

Key terms in this question

selective breeding · chemical fertilisers · yield

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