Decay Lesson | GCSE Biology OCR 21st Century Higher Triple

Decay

This lesson covers:

What 'decomposition' is
The ideal conditions for decomposition

Decomposition

Decomposition, often called 'rotting', is the process by which dead organic matter is broken down into simpler organic or inorganic substances, such as carbon dioxide, water, simple sugars, and minerals.

Decomposition is essential for the recycling of elements throughout an ecosystem.

Hands holding decomposed leaves and fresh leaves to illustrate the decomposition process.

For example, when leaves fall from a tree and are slowly broken down in the soil, we say that they are decomposing. This recycles the carbon, nitrogen, magnesium etc. and makes them available for the plants to absorb and use again.

Detritus feeders and decomposers

Decomposition is carried out by two groups of organisms: detritus feeders (detritivores), and decomposers.

Illustration showing detritivores like a worm and woodlice, and decomposers like bacteria and fungi.

Detritus feeders - small animals like worms and woodlice that feed on dead organic matter.

Decomposers - microorganisms, such as bacteria and fungi.

What is decay?

The formation of urea by the liver

The production of glucose from carbon dioxide and water

The breakdown of organic matter by the action of decomposers

Which of the following are detritus feeders?

Worms

Fungi

Bacteria

Woodlice

Factors that affect the rate of decomposition

The rate of decomposition is affected by 3 environmental conditions:

Diagram showing oxygen molecules, illustrating one of the factors affecting the rate of decomposition.

1Oxygen availability

Higher oxygen ➔ more aerobic respiration ➔ more energy available ➔ faster growth and decomposition

Illustration showing temperature as a factor affecting decomposition with fire and ice cubes.

2Temperature

Higher temperature ➔ particles have more kinetic energy & enzymes are closer to optimum temperature ➔ higher rate of reactions ➔ more decomposition

However, if temperature rises too high, it will denature enzymes, decreasing the rate of reaction and therefore decreasing the rate of decomposition.

Illustration showing two water droplets with a label reading water.

3Water content

Decomposers need water to survive, so the rate of decomposition increases in moist conditions.

However, if the soil becomes waterlogged then the oxygen levels will fall, which will decrease the rate of decomposition.

What effect would lowering the temperature have on the rate of decay of an apple?

No effect on the rate of decay

Decrease the rate of decay

Increase the rate of decay

Oxygen is important for decomposition.

What process do bacteria need oxygen for?

Aerobic respiration

Why could the rate of decomposition fall if soil becomes waterlogged?

What does anaerobic mean?

Without oxygen

With air

Without air

With oxygen