Decomposition and the Role of Microorganisms — AQA GCSE Biology
Decomposers break down dead material, recycling nutrients back into the ecosystem. The rate of decay depends on the conditions.
What is decomposition?
Decomposition (decay) is the breakdown of dead organisms and waste by microorganisms (decomposers, mainly bacteria and fungi). It releases nutrients back into the soil and carbon dioxide back into the air, recycling materials for new growth.
Factors affecting the rate of decay
Decay is faster when conditions suit the microorganisms:
- Temperature — warmer (up to an optimum) speeds up decay; too hot denatures the microorganisms' enzymes; too cold slows it.
- Moisture (water) — decay is faster in moist conditions.
- Oxygen (air) — most decomposers respire aerobically, so more oxygen speeds decay.
Composting
Gardeners and farmers use these conditions to make compost — decayed material used as a natural fertiliser. Good compost needs warmth, moisture and oxygen.
Anaerobic decay and biogas
In the absence of oxygen, anaerobic decay produces methane gas (biogas). Biogas generators use microorganisms to produce methane from waste, which can be burned as a fuel.
Required practical (rate of decay)
You may investigate the rate of decay of milk (e.g. measuring pH change as it sours) at different temperatures, calculating rate as 1 ÷ time.
Exam tips
- Decomposers are microorganisms (bacteria and fungi) that recycle nutrients.
- Learn the three factors affecting decay rate: temperature, moisture, oxygen.
- Compost needs warmth, moisture and oxygen (aerobic).
- Anaerobic decay produces methane (biogas), used as a fuel.