# Explain how the thermal properties of water, arising from hydrogen bonding, make it important for the survival of aquatic organisms during freezing conditions.

> IB DP Biology Higher Level (2023 syllabus) — A1.1 Water · Explain · 4 marks

## Mark scheme (4 marks)

1. Water has a high latent heat of fusion, meaning a large amount of energy must be removed before water changes from liquid to solid.
2. This is because hydrogen bonds between water molecules must be broken / reorganised during freezing, requiring the removal of significant energy.
3. Ice is less dense than liquid water because hydrogen bonds hold water molecules further apart in the crystalline lattice of ice, so ice floats on the surface.
4. The floating ice layer acts as an insulator, preventing the water beneath from freezing and allowing aquatic organisms to survive.

## Key terms

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

## 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)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-thermal-properties-of-df7049ea) · Published by Druglandscape Ltd.