Students should be able to explain how temperature, water and availability of oxygen affect the rate of decay of biological material. • Students should be able to calculate rate changes in the decay of biological material. • Gardeners and farmers try to provide optimum conditions for rapid decay of waste biological material. The compost produced is used as a natural fertiliser for growing garden plants or crops. • Anaerobic decay produces methane gas. Biogas generators can be used to produce methane gas as a fuel.