Explain how the use of fertilisers can help improve food security, and describe one problem that their overuse can cause.

Edexcel GCSE Biology (1BI0) — 9.2 Food security · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Fertilisers supply essential nutrients such as nitrogen, phosphorus and potassium to the soil, which plants absorb for growth.

This nutrient enrichment promotes faster plant development and higher crop yields, helping to meet the food demand of a growing population.

However, excessive fertiliser use can lead to eutrophication when the excess nutrients run off into rivers and lakes.

The resulting algal blooms block light penetration and, when the algae die, their decomposition consumes oxygen, creating hypoxic conditions that harm aquatic life.

Examiner tips

  • Use the exact terms "nitrogen, phosphorus, potassium" and "eutrophication". Explain the chain from fertiliser to algal bloom to oxygen depletion. Keep each point brief and directly linked to the marks.
  • Show cause–effect relationships: fertiliser → nutrient supply → yield; overuse → runoff → eutrophication → hypoxia.

Common mistakes

  • Confusing fertiliser benefits with pesticide effects. Using vague terms like "more nutrients" without naming N, P, K. Failing to mention the oxygen depletion step in eutrophication.

Mark scheme (4 marks)

  1. Fertilisers provide essential nutrients to the soil / plants
  2. This improves plant growth / increases crop yield
  3. Overuse of fertilisers can cause eutrophication (fertilisers run off into bodies of water causing algal blooms)
  4. Algal blooms block light / decomposers break down dead algae reducing oxygen levels, harming aquatic organisms

Key terms in this question

fertilisers · food security

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