Explain how carbon stored in the bodies of dead animals is returned to the atmosphere as carbon dioxide.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
When animals die, their bodies contain large amounts of carbon stored in organic compounds such as proteins and fats.
Model answer (4 marks)
1. Decomposers such as bacteria and fungi colonise the carcass and secrete enzymes that break down proteins and fats into simpler organic molecules.
2. The enzymes catalyse the hydrolysis of complex compounds, producing small organic acids, alcohols and sugars.
3. These simpler compounds are then used as a food source by the decomposers, which respire them, oxidising the carbon atoms.
4. During respiration the carbon atoms are released as carbon dioxide, which is expelled into the atmosphere.
2. The enzymes catalyse the hydrolysis of complex compounds, producing small organic acids, alcohols and sugars.
3. These simpler compounds are then used as a food source by the decomposers, which respire them, oxidising the carbon atoms.
4. During respiration the carbon atoms are released as carbon dioxide, which is expelled into the atmosphere.
Examiner tips
- Use the word "decomposers" and mention bacteria/fungi. Show the step of enzyme action. Explain that respiration releases CO₂. Keep the answer concise and use correct terminology.
Common mistakes
- Confusing decomposition with photosynthesis. Omitting the role of enzymes or respiration. Using vague terms like "break down" without specifying decomposers.
Mark scheme (4 marks)
- Decomposers / microorganisms / bacteria and fungi break down / digest the dead animal material
- Decomposers release enzymes that catalyse the breakdown of organic compounds into simpler organic matter
- Decomposers (and other organisms) respire the organic compounds / use them as a food source in respiration
- Carbon dioxide is released into the atmosphere as a product of respiration
Related
- All Pearson Edexcel International GCSE Biology (4BI1) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →