How Does Decomposition Work? GCSE Biology
Learn how decomposers break down dead material, return carbon dioxide and mineral ions, and why temperature, water and oxygen affect decay in GCSE Biology.
Decomposition works when microorganisms break down dead plants, dead animals and waste material. This returns materials to the environment so they can be used again by living organisms. In AQA GCSE Biology, decomposition is part of Ecology and is biology-only content for both Foundation and Higher tier.
How do decomposers break material down?
Decomposers are microorganisms, such as bacteria and fungi. They secrete enzymes onto dead material. The enzymes break large molecules into small, soluble molecules, which can then diffuse into the microorganisms. An enzyme is a substance that speeds up a reaction without being used up.
As microorganisms break down material, mineral ions are returned to the soil, where plants can take them up. Microorganisms also respire, returning carbon to the atmosphere as carbon dioxide. This helps explain why decomposition is important in the cycling of materials through an ecosystem.
What affects the rate of decay?
Temperature, water and oxygen all affect how quickly biological material decays. Warm, moist conditions generally help microorganisms break it down faster, but very high temperatures can stop their enzymes working. Oxygen allows aerobic respiration, which helps decomposers remain active. If oxygen is unavailable, anaerobic decay can take place and produce methane gas.
For example, gardeners provide suitable conditions for garden waste to decay into compost. The compost can then be used as a natural fertiliser for plants. Methane from anaerobic decay can also be collected in a biogas generator and used as a fuel.
In the required practical, you investigate how temperature affects the decay of fresh milk by measuring its change in pH. To compare temperatures fairly, use the same volume of milk and measure pH over the same length of time. A faster pH change indicates a faster rate of decay.
Common exam mistake: saying that dead material simply ‘disappears’. Describe what breaks it down and where the materials go: decomposers return mineral ions to the soil and carbon dioxide to the atmosphere.
