A peat bog is a waterlogged ecosystem where dead plant material accumulates over thousands of years rather than fully decomposing. Explain why dead plant material accumulates in a peat bog instead of being fully broken down, and explain what would happen to the rate of decomposition if the peat bog dried out.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Peat bogs cover around 3% of the Earth's land surface and store vast amounts of carbon. Scientists are concerned about the effects of draining peat bogs for agriculture.
Model answer (5 marks)
In a peat bog the waterlogged soil is saturated and the pore spaces are filled with water, so the oxygen concentration is very low or absent. Because of this, decomposer microorganisms cannot carry out aerobic respiration and the only decomposition that occurs is anaerobic, which is much slower. Consequently dead plant material accumulates.
If the bog were to dry out, oxygen would become available again. Aerobic decomposers would then become active and the rate of decomposition would increase markedly.
If the bog were to dry out, oxygen would become available again. Aerobic decomposers would then become active and the rate of decomposition would increase markedly.
Examiner tips
- Use the terms "waterlogged", "low oxygen", "anaerobic decomposition" and "aerobic decomposition"
- Explain the link between oxygen availability and the type of decomposition
- Show the cause–effect chain: drying → more oxygen → faster decomposition
Common mistakes
- Confusing anaerobic with aerobic decomposition
- Failing to mention that anaerobic decomposition is slower
- Not linking the drying of the bog to increased oxygen and faster decomposition
Mark scheme (5 marks)
- The waterlogged conditions mean there is little or no oxygen available
- Decomposers / microorganisms cannot carry out aerobic decomposition without oxygen
- Anaerobic decomposition is much slower than aerobic decomposition, so material accumulates
- If the bog dried out, oxygen availability would increase
- The rate of decomposition would increase because aerobic decomposition / decomposers would be more active
Key terms in this question
Related
- All OCR A-Level Biology B — Advancing Biology (H422) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Energy budgets and ecosystems questions
- A group of students is investigating the decomposition of leaf litter in two for…
- A marine ecosystem contains phytoplankton (producers), krill (primary consumers)…
- A wildlife organisation is investigating the carbon cycle in a woodland ecosyste…
- A farmer wants to improve the fertility of their soil by making compost from dea…