Decomposer

In the syllabus and the exam

Decomposers are organisms, mainly bacteria and fungi, that break down dead organisms and waste products into simpler inorganic substances, and this process is examined specifically for its role in nutrient cycling, allowing minerals locked up in dead matter to be released and reused by producers, rather than being lost from the ecosystem permanently. Candidates should be able to explain decomposition as an essential step in cycles such as the nitrogen cycle and the carbon cycle, distinguishing decomposers from detritivores (larger organisms such as earthworms and millipedes that physically break dead matter into smaller pieces, increasing the surface area available for decomposers, but which do not themselves chemically break down the material in the same way). A common error is describing a decomposer simply as something that 'eats dead things', without linking this to the release of nutrients back into the ecosystem, which is the key exam-relevant consequence. Candidates should also avoid confusing decomposers with consumers: consumers occupy a defined trophic level and feed on living or recently killed organisms within a food chain, whereas decomposers act outside the normal food chain structure on dead organic matter from any trophic level at once. Without decomposers, exam scenarios often ask candidates to predict that dead matter and waste would accumulate indefinitely and nutrients would become permanently locked away from producers. Candidates should also be able to name the specific stage of the carbon cycle at which decomposers act, releasing carbon dioxide back into the atmosphere through their own respiration as they break down dead organic matter.

Example

Fungi and bacteria in soil break down a fallen leaf into simpler substances, releasing minerals such as nitrate back into the soil where a plant's roots can absorb them again.

Related terms

Food chainProducerEcosystem

Source:SRC-DSKP-EN