# Explain how the thermal properties of water help maintain stable internal temperatures in living organisms.

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

## Mark scheme (4 marks)

1. Water has a high specific heat capacity, meaning a large amount of energy is required to raise its temperature by 1 °C (per unit mass).
2. This is because hydrogen bonds between water molecules must absorb energy before the molecules can move faster (increase in kinetic energy), so temperature rises slowly.
3. Because the cytoplasm and body fluids are largely water, organisms are buffered against rapid or extreme fluctuations in internal temperature.
4. Water also has a high latent heat of vaporisation, so evaporation of water from body surfaces (e.g. sweating / transpiration) removes a large amount of heat energy, providing an effective cooling mechanism.

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