Explain how carbon from carbon dioxide in the atmosphere is transferred into the bodies of animals, and how it is returned to the atmosphere through two different processes.

Edexcel GCSE Biology (1BI0) — 9.3 Material 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)

Plants absorb CO₂ from the atmosphere during photosynthesis, converting it into organic matter.
Animals obtain carbon by eating plants or other animals, so carbon is transferred up the food chain.
Carbon is returned to the atmosphere as CO₂ by respiration in plants, animals and decomposers.
Carbon is also returned to the atmosphere as CO₂ by combustion of organic material, fossil fuels or biomass.

Examiner tips

  • Use the word ‘absorb’ for photosynthesis and ‘obtain’ for eating. Show the two return routes: respiration and combustion. Keep the answer concise and use the exact terms from the mark scheme.

Common mistakes

  • Mixing up absorption with release; forgetting to mention respiration. Using ‘burn’ instead of ‘combustion’. Including extra processes not asked for, such as decomposition alone.

Mark scheme (4 marks)

  1. Plants absorb carbon dioxide from the atmosphere during photosynthesis
  2. Animals obtain carbon by eating (consuming) plants or other animals / carbon passes along a food chain
  3. Carbon is returned to the atmosphere as carbon dioxide by respiration (in plants, animals or decomposers)
  4. Carbon is returned to the atmosphere as carbon dioxide by combustion of organic material / fossil fuels / biomass

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