Describe the role of decomposers in the carbon cycle.

Pearson Edexcel International GCSE Biology (4BI1) — 4.3 Cycles within ecosystems · Describe · 4 marks · View as Markdown

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

Dead leaves and animal remains accumulate on a forest floor. Over time, these materials disappear and carbon dioxide is released back into the atmosphere.

Model answer (4 marks)

Decomposers secrete enzymes that break down dead plant and animal material into simple compounds.
They then carry out respiration, oxidising these compounds and releasing carbon dioxide.
Thus carbon is returned to the atmosphere as CO₂, completing the carbon cycle.
The speed of decomposition depends on temperature, water availability and oxygen levels.

Examiner tips

  • Use the word "decomposers" and "carbon dioxide". Show the sequence: enzymes → breakdown → respiration → CO₂ release. Mention the factors that affect the rate.
  • common_mistakes
  • :
  • Confusing decomposers with producers. Forgetting to link enzyme action to CO₂ release. Omitting the factors that influence decomposition rate.

Mark scheme (4 marks)

  1. Decomposers release enzymes that break down dead plant and animal material
  2. Decomposers carry out respiration, releasing carbon dioxide into the atmosphere
  3. This returns carbon (as carbon dioxide) from dead organic matter to the atmosphere
  4. The rate of decomposition is affected by temperature, water availability or oxygen availability

Key terms in this question

decomposers · carbon cycle

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