# Explain why the net primary productivity (NPP) of an ecosystem is always less than the gross primary productivity (GPP), and outline how NPP is used to support consumers at higher trophic levels.

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

## Mark scheme (4 marks)

1. GPP is the total rate of photosynthetic fixation of energy/carbon by producers in an ecosystem
2. Producers use a portion of GPP in their own cellular respiration, releasing energy as heat, so NPP = GPP minus respiration losses
3. NPP represents the net gain in organic biomass by producers per unit time and is therefore the energy/matter available to primary consumers
4. Only a fraction of NPP passes to the next trophic level because energy is lost through consumer respiration, undigested material in faeces, and matter entering detritus/decomposers

## Key terms

- [gross primary productivity (GPP)](https://www.gradenine.co.uk/glossary/gross-primary-productivity-gpp)
- [net primary productivity (NPP)](https://www.gradenine.co.uk/glossary/net-primary-productivity-npp)
- [trophic level](https://www.gradenine.co.uk/glossary/trophic-level)

## 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-why-the-net-primary-productivity-9f6543c0) · Published by Druglandscape Ltd.