Explain how the thermal properties of water help maintain stable internal temperatures in living organisms.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Water has a high specific heat capacity, so a large amount of energy is required to raise its temperature by 1 °C per unit mass. This is because hydrogen bonds between water molecules must absorb energy before the molecules can move faster, so temperature rises slowly. Since the cytoplasm and body fluids are largely water, organisms are buffered against rapid or extreme fluctuations in internal temperature. Water also has a high latent heat of vapourisation; evaporation of water from body surfaces (e.g. sweating or transpiration) removes a large amount of heat energy, providing an effective cooling mechanism.
Examiner tips
- Use the phrase "high specific heat capacity" and explain the role of hydrogen bonds. Mention that cytoplasm/body fluids are largely water. Include the high latent heat of vapourisation and its cooling effect. Keep answer concise and use UK spelling.
Common mistakes
- Forgetting to explain why hydrogen bonds require energy. Using the wrong term (e.g. latent heat of fusion instead of vapourisation). Over‑extending the answer with irrelevant details.
Mark scheme (4 marks)
- 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).
- 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.
- Because the cytoplasm and body fluids are largely water, organisms are buffered against rapid or extreme fluctuations in internal temperature.
- 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.
Related
- All IB DP Biology Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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