# Explain how hydrogen bonding between water molecules gives water a high latent heat of vaporisation, and outline one way this property is significant to living organisms.

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

## Mark scheme (4 marks)

1. Hydrogen bonds form between water molecules due to the polar nature of the O–H bond / the partial negative charge on oxygen and partial positive charge on hydrogen.
2. A large amount of energy is required to break the many hydrogen bonds holding water molecules together before vaporisation can occur.
3. This means that the evaporation of a small amount of water removes a large amount of heat energy from the surface / organism.
4. One biological significance outlined — e.g. sweating / transpiration / panting acts as an effective cooling mechanism, helping to maintain a stable body/leaf temperature (thermoregulation).

## Key terms

- [latent heat of vaporisation](https://www.gradenine.co.uk/glossary/latent-heat-of-vaporisation)
- [hydrogen bond](https://www.gradenine.co.uk/glossary/hydrogen-bond)

## 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-hydrogen-bonding-between-water-85b3cf0f) · Published by Druglandscape Ltd.