7.2.3 Decomposition (Biology Only)

What three main factors affect the rate of decomposition?

Temperature, water, and availability of oxygen.

How does temperature affect the rate of decomposition?

Chemical reactions work faster in warmer conditions, but if too hot enzymes denature and decomposition stops.

Why does water speed up decomposition?

Microorganisms grow faster in moist conditions as water is needed for respiration and makes food easier to digest.

Why is oxygen important in decomposition?

Most decomposers respire aerobically, so more oxygen increases the rate of decay.

What is produced when biological material decays?

Compost.

Why is compost useful to farmers and gardeners?

It is used as a natural fertiliser, returning nutrients to the soil.

How do gardeners provide optimum conditions for composting?

They ensure oxygen and warmth are present, so microorganisms respire aerobically and heat speeds decay.

What gas is produced when microorganisms decompose waste anaerobically?

Methane.

How is methane from decomposition used?

It can be burnt as a fuel.

What are biogas generators used for?

Producing methane by anaerobic decomposition of waste.

Why must biogas generators be kept at a constant temperature of around 30°C?

So microorganisms keep respiring without being killed or slowed by cold.

Why can methane not be stored as a liquid?

It must be used immediately because it cannot be stored safely as a liquid.

How can you investigate the effect of temperature on decay using milk?

Use milk with phenolphthalein indicator and sodium carbonate, add lipase at different temperatures, and time how long it takes for the pink colour to disappear.

What does the disappearance of the pink colour in the milk decay experiment show?

The pH has decreased due to decomposition, meaning lipase has broken down the milk fats into fatty acids.