Decomposition

This lesson covers decomposition — the breakdown of dead organisms and waste material — as required by the Edexcel GCSE Combined Science specification (1SC0). You need to understand the role of decomposers, the factors that affect the rate of decomposition, and the importance of decomposition for nutrient recycling.

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What Is Decomposition?

Decomposition is the process by which dead organisms and biological waste (e.g. fallen leaves, faeces, dead animals) are broken down into simpler substances. This process is carried out by decomposers.

Decomposers are organisms that feed on dead or decaying material. The main decomposers are:

• Bacteria — microscopic prokaryotes found in soil, water and on surfaces
• Fungi — including moulds and mushrooms; they secrete enzymes onto dead material and absorb the products

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How Decomposition Works

Decomposers break down dead organic matter through a process of extracellular digestion:

1. The decomposer (bacterium or fungus) secretes enzymes onto the dead material
2. The enzymes break down large, complex molecules into smaller, soluble molecules
3. The decomposer absorbs the small molecules for nutrition
4. Simple inorganic substances (e.g. mineral ions, carbon dioxide, water) are released back into the environment