7.2.3: Decomposition (biology only)
Not started yet — this one needs some love.
Decay of biological material is affected by temperature, water and availability of oxygen.
Higher temperature can increase decay rate up to an optimum because microorganisms and their enzymes work faster.
Water is needed for decay by microorganisms, so very dry conditions slow decay.
Oxygen allows aerobic decay; anaerobic decay happens without oxygen and produces methane gas.
Rate of decay can be calculated from the change in biological material divided by time.
Gardeners and farmers try to provide optimum conditions for rapid decay of waste biological material.
Compost produced by decay is used as a natural fertiliser for growing garden plants or crops.
Biogas generators can be used to produce methane gas as a fuel.
Common exam mistakes
Do not say decomposers are used up during decay; microorganisms digest material and use the products.
In RP10: Decay and temperature, a faster fall in pH means faster decay because fatty acids are being produced.
Do not mix up aerobic and anaerobic decay: methane is linked to anaerobic decay.
In RP10, temperature is the independent variable, so it should not be listed as a control variable.
If improving a decay investigation, mention repeats and calculating a mean, not just "do repeats".