Describe how decomposers return carbon and mineral ions to the environment, and explain why this is important for producers.

AQA GCSE Biology (8461) — 4.7.2 Organisation of an ecosystem · Describe · 4 marks · View as Markdown

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

Model answer (4 marks)

Decomposers secrete enzymes that break down dead plant and animal matter into simple compounds.
The carbon in the material is oxidised to carbon dioxide, which is released into the atmosphere.
Mineral ions such as nitrogen, phosphorus and potassium are released into the soil.
Producers use the CO₂ for photosynthesis and absorb the mineral ions from the soil to build proteins and other cellular components.

Examiner tips

  • Use the word ‘decomposers’ and ‘producers’ explicitly. Show the two steps – release of CO₂ and return of mineral ions. Explain the role of CO₂ and minerals in photosynthesis and growth. Keep each point short and use correct terminology.

Common mistakes

  • Confusing decomposers with producers. Omitting the release of CO₂ or the return of mineral ions. Using vague terms like ‘break down’ without mentioning enzymes or oxidation. Failing to link the returned substances to photosynthesis or growth.

Mark scheme (4 marks)

  1. Decomposers release enzymes which break down dead plant and animal material
  2. Carbon is converted to carbon dioxide and released into the atmosphere / mineral ions are returned to the soil
  3. Producers use carbon dioxide for photosynthesis
  4. Producers absorb mineral ions from the soil for growth / to make proteins and other biological molecules

Key terms in this question

decomposers · producers · mineral ions

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