# Explain how the properties of water resulting from hydrogen bonding between water molecules contribute to the survival of aquatic organisms during periods of freezing temperatures.

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

## Mark scheme (4 marks)

1. Water has a lower density as ice than as liquid water / ice is less dense than liquid water
2. In ice, hydrogen bonds are fixed in a lattice / regular crystalline arrangement that holds molecules further apart than in liquid water, explaining the lower density
3. Ice floats and forms an insulating layer on the surface of water bodies, preventing the water below from freezing
4. Water's high specific heat capacity / latent heat of fusion means a large amount of energy must be removed before water freezes, buffering temperature change and maintaining liquid conditions for longer

## 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)
- [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-properties-of-water-aca33e52) · Published by Druglandscape Ltd.