Explain how the carbon stored in a dead tree is returned to the atmosphere.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Decomposers such as bacteria and fungi break down the dead tree, a process called decomposition. During this, they respire and release carbon dioxide (CO₂) into the atmosphere. If the dead material is buried and compressed over millions of years, it may become fossil fuels; when these fuels are later burned, they also release CO₂ back into the air.
Examiner tips
- Use the word ‘decomposers’ and mention bacteria/fungi; show the respiration step; include fossil fuel formation and combustion; keep answer concise and to the point.
Common mistakes
- Forgetting to mention decomposers; confusing decomposition with combustion; omitting the fossil fuel step or not linking it to carbon release.
Mark scheme (4 marks)
- Decomposers / bacteria / fungi break down the dead tree (decomposition / decay)
- Decomposers respire, releasing carbon dioxide into the atmosphere
- Carbon is also stored in fossil fuels if dead material is compressed / buried over millions of years (reference to incomplete decomposition leading to fossil fuel formation)
- Burning / combustion of wood (or fossil fuels formed from organic matter) releases carbon dioxide into the atmosphere
Related
- All WJEC GCSE Biology (Wales) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →