Decomposers such as bacteria and fungi play an important role in the recycling of nutrients in ecosystems. Explain how the process of decomposition and decay returns nutrients to the soil, and describe TWO environmental conditions that slow down the rate of decomposition.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A gardener notices that dead plant material left in a cold, waterlogged compost bin breaks down much more slowly than material in a warm, well-aerated bin.
Model answer (5 marks)
Decomposers such as bacteria and fungi digest dead plant material, breaking complex organic molecules into simple compounds.
The digestion releases nutrients (e.g. nitrogen, phosphorus, potassium) as inorganic ions into the soil, making them available for plant uptake.
Low temperature reduces the activity of decomposer enzymes, so the rate of digestion and nutrient release is slower.
Waterlogged, anaerobic conditions limit the oxygen available for aerobic decomposers, so decomposition is also slowed and nutrients remain locked in organic matter.
These conditions therefore reduce the speed at which nutrients are recycled back into the soil, limiting plant access to essential minerals.
The digestion releases nutrients (e.g. nitrogen, phosphorus, potassium) as inorganic ions into the soil, making them available for plant uptake.
Low temperature reduces the activity of decomposer enzymes, so the rate of digestion and nutrient release is slower.
Waterlogged, anaerobic conditions limit the oxygen available for aerobic decomposers, so decomposition is also slowed and nutrients remain locked in organic matter.
These conditions therefore reduce the speed at which nutrients are recycled back into the soil, limiting plant access to essential minerals.
Examiner tips
- Use the term ‘decomposers’ and specify bacteria/fungi. Explain the release of inorganic nutrients. Give two specific conditions: low temperature and anaerobic waterlogged soil. Link each condition to slower nutrient recycling.
Common mistakes
- Confusing decomposition with photosynthesis. Forgetting to mention nutrient release. Using vague terms like ‘slow down’ without specifying temperature or oxygen.
Mark scheme (5 marks)
- Decomposers (bacteria and fungi) break down / digest dead organic material / organisms
- Decomposers release nutrients / minerals into the soil (so they can be absorbed by plants)
- Low temperature slows decomposition because decomposers / enzymes are less active
- Waterlogged / anaerobic conditions slow decomposition because decomposers need oxygen (for aerobic respiration)
- Linking both conditions back to slower nutrient recycling / reduced availability of minerals for plants
Key terms in this question
decomposers · decomposition · nutrients
Related
- All Edexcel A-Level Biology A: Salters-Nuffield (9BN0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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