Explain how the high latent heat of vaporisation of water, arising from hydrogen bonding, is significant for living organisms.

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

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Hydrogen bonds must be broken for water molecules to escape the liquid surface and vaporise.
A large quantity of heat energy is absorbed per gram of water evaporated, giving water a high latent heat of vaporisation.
This allows evaporative cooling to be an effective mechanism for thermoregulation in organisms.
The high latent heat also stabilises aquatic environments by resisting rapid evaporation, helping to maintain stable habitats for aquatic organisms.

Examiner tips

  • Use the term ‘latent heat of vaporisation’ and link it to hydrogen bonding. Show the chain: H‑bond breaking → heat absorbed → cooling. Mention both body and environmental contexts.
  • common_mistakes
  • :
  • Confusing latent heat of fusion with latent heat of vaporisation. Forgetting to mention hydrogen bonds or the stabilising effect on aquatic habitats.

Mark scheme (4 marks)

  1. Hydrogen bonds must be broken for water molecules to escape the liquid surface and vaporise
  2. A large quantity of heat energy is absorbed / removed from the surface or organism per gram of water evaporated
  3. This allows evaporative cooling to be an effective mechanism for thermoregulation / temperature regulation in organisms
  4. The high latent heat of vaporisation also stabilises aquatic / oceanic environments by resisting rapid evaporation, helping to maintain stable habitats for aquatic organisms

Key terms in this question

latent heat of vaporisation · hydrogen bonding

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