# Explain how detritivores and decomposers contribute to the cycling of matter in an ecosystem, and distinguish their roles from those of producers and consumers.

> IB DP Biology Higher Level (2023 syllabus) — C4.2 Transfers of energy and matter · Explain · 4 marks

## Mark scheme (4 marks)

1. Detritivores physically break down (fragment) dead organic matter / detritus into smaller pieces, increasing the surface area available for decomposer action.
2. Decomposers (bacteria and fungi) chemically digest / mineralise organic compounds via extracellular enzymes, releasing inorganic nutrients (e.g. nitrate, phosphate, carbon dioxide) back into the abiotic environment.
3. Producers (autotrophs) incorporate inorganic nutrients / CO₂ into organic compounds via photosynthesis, thereby moving matter from the abiotic to the biotic component of the ecosystem.
4. Consumers obtain organic matter by feeding on other organisms (heterotrophically), transferring matter along the food chain but not returning it to the inorganic pool, unlike detritivores and decomposers which ultimately return matter to the abiotic environment / close the cycle.

## Key terms

- [detritivore](https://www.gradenine.co.uk/glossary/detritivore)
- [decomposer](https://www.gradenine.co.uk/glossary/decomposer)

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-detritivores-and-decomposers-contribute-827a460e) · Published by Druglandscape Ltd.