# Explain the role of decomposers in the cycling of phosphorus within an ecosystem.

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

## Mark scheme (4 marks)

1. Decomposers (bacteria and fungi) break down dead organic matter / detritus containing phosphorus compounds (e.g. nucleic acids, phospholipids, ATP)
2. Decomposers release inorganic phosphate ions (PO₄³⁻) into the soil / water through the process of mineralisation
3. Inorganic phosphate ions are absorbed / taken up by producers (plants / algae) via roots / active transport
4. This cycling ensures phosphorus is returned to the biotic components of the ecosystem / prevents permanent loss of phosphorus from the ecosystem / allows phosphorus to be reused by living organisms

## Key terms

- [decomposers](https://www.gradenine.co.uk/glossary/decomposers)
- [cycling](https://www.gradenine.co.uk/glossary/cycling)

## Related

- [Revision notes for IB DP Biology Standard 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-the-role-of-decomposers-in-dda6947f) · Published by Druglandscape Ltd.