# Explain how the adaptations of deep-sea fish allow them to survive at high hydrostatic pressures.

> IB DP Biology Standard Level (2023 syllabus) — B4.1 Adaptation to environment · Explain · 4 marks

> Deep-sea fish live at depths exceeding 1000 m, where hydrostatic pressure can be more than 100 times greater than at the ocean surface. Many species lack a swim bladder and have unusually flexible, low-density body structures.

## Mark scheme (4 marks)

1. Absence of a gas-filled swim bladder prevents compression/collapse of the body cavity at high pressure
2. Cell membranes contain a high proportion of unsaturated/polyunsaturated fatty acids, maintaining membrane fluidity at high pressure / low temperature
3. Proteins/enzymes are adapted (e.g. more flexible tertiary structures / stabilised by pressure-resistant amino acid sequences) to function at high pressure
4. Soft, gelatinous/flexible body tissues with high water content equalise internal and external pressure, preventing crushing

## Key terms

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

## 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-how-the-adaptations-of-deep-sea-589b83a9) · Published by Druglandscape Ltd.