# A deep-sea fish lives in very cold, oxygen-poor water at great depth. Explain why the fish must still carry out respiration continuously, referring to specific uses of energy in the fish's cells.

> Pearson Edexcel A-Level Biology A (9BI0) — Topic 5 Energy for Life · Explain · 5 marks

> Deep-sea fish face extreme conditions including near-freezing temperatures, very low oxygen availability, and crushing pressures. Despite these challenges, their cells remain metabolically active.

## Mark scheme (5 marks)

1. Respiration releases energy (from glucose/food) for use in the cell
2. Energy is needed for movement / contraction of muscle fibres
3. Energy is needed for active transport (to move substances across cell membranes / against a concentration gradient)
4. Energy is needed to maintain body temperature / for warmth in the cold deep-sea environment
5. Energy is needed for the synthesis of large molecules (e.g. proteins from amino acids / building new cells)

## Key terms

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

## Related

- [Revision notes for Pearson Edexcel A-Level Biology A (9BI0)](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/a-deep-sea-fish-lives-in-very-c7e0ee30) · Published by Druglandscape Ltd.