Explain why removing all the decomposers from a woodland ecosystem would eventually cause the plants in that woodland to stop growing, even if rainfall and light levels remained unchanged.

Eduqas GCSE Biology — 1.6.2 Nutrient cycles · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Decomposers break down dead organic matter and leaf litter, releasing mineral nutrients into the soil.
Without decomposers these nutrients remain locked in the dead material and are not returned to the soil.
Consequently the soil becomes deficient in essential minerals such as nitrates and phosphates.
Plants cannot absorb enough of these nutrients, so their growth eventually stops.

Examiner tips

  • Use the term ‘decomposers’ and ‘mineral nutrients’ to show understanding of the cycle.
  • Explain the chain: decomposition → nutrient release → plant uptake → growth.
  • Mention that rainfall and light are unchanged to focus on nutrient limitation.
  • Keep the answer concise and directly linked to the marks scheme.

Common mistakes

  • Confusing decomposers with predators or producers.
  • Failing to mention that nutrients are locked in dead matter.
  • Using vague terms like ‘nutrients’ without specifying minerals such as nitrates or phosphates.

Mark scheme (4 marks)

  1. Decomposers break down dead organic matter / dead organisms / leaf litter
  2. Decomposition releases (mineral) nutrients / ions into the soil
  3. Without decomposers, nutrients / minerals become locked up in dead matter and are not returned to the soil
  4. Plants cannot absorb sufficient minerals / nutrients (e.g. nitrates / phosphates) needed for growth

Key terms in this question

decomposers

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