Decomposition (biology only) — AQA GCSE Biology
Test yourself on Decomposition (biology only) with AQA GCSE practice questions.
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Decomposition (biology only) explained
Decay is the breakdown of biological material by microorganisms such as bacteria and fungi.
Read the full explanation
Their enzymes digest the material, and the rate depends on conditions. Warmth increases enzyme activity and microbial growth, so decay is faster up to an optimum; very high temperatures denature enzymes and slow or stop decay. Moisture is needed because microorganisms and their enzymes work in solution, so damp conditions speed up decay while dry conditions slow it. Oxygen is needed for aerobic respiration by decomposers, so plenty of oxygen increases the rate; waterlogged or sealed conditions limit oxygen and slow aerobic decay. These principles explain why food is refrigerated, dried, salted or vacuum-packed to preserve it.
Your focus
- Explain how temperature affects the rate of decay and the role of enzyme denaturation.
- Describe how water and oxygen availability affect the rate of decomposition.
- Apply these factors to explain methods of food preservation.
Decomposition (biology only) exam tips
Marking Points
- Warm temperatures increase enzyme activity and microbial growth, so decay is faster up to an optimum temperature.
- Very high temperatures denature the enzymes of decomposers, so the rate of decay falls.
- Moist conditions allow microorganisms and their enzymes to work, so decay is faster in damp material than in dry material.
- Availability of oxygen supports aerobic respiration in decomposers, so more oxygen increases the rate of decay.
- Limited oxygen, for example in waterlogged or sealed conditions, slows aerobic decay and can favour anaerobic decomposers.
Examiner Tips
- 💡Use the word 'optimum' when describing temperature and explain what happens above it.
- 💡Link each factor to the microorganisms: enzymes, respiration or growth, rather than treating decay as a simple chemical reaction.
- 💡When explaining food preservation, name the factor that is controlled and state how it slows decay.
Common Mistakes
- Saying higher temperature always increases decay; the correction is that decay increases up to an optimum, then enzymes denature and the rate falls.
- Thinking water is a reactant that is used up; the correction is that water provides the moist conditions needed for microbial enzymes to work.
- Ignoring oxygen and assuming decay is the same in all conditions; the correction is that oxygen availability strongly affects the rate of aerobic decomposition.