Explain how the high specific heat capacity of water arises from hydrogen bonding between water molecules, and outline one consequence of this property for aquatic organisms.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Water molecules are polar and form hydrogen bonds with each other.
Because of these hydrogen bonds a large amount of energy is required to increase the kinetic energy of the water; energy must first be used to break or overcome the hydrogen bonds before the molecules can move faster.
Consequently water temperature changes slowly and resists rapid fluctuations.
One consequence for aquatic organisms is that the relatively stable temperature of lakes, oceans and rivers prevents extreme thermal fluctuations, allowing organisms to maintain enzyme function and metabolic processes.
Because of these hydrogen bonds a large amount of energy is required to increase the kinetic energy of the water; energy must first be used to break or overcome the hydrogen bonds before the molecules can move faster.
Consequently water temperature changes slowly and resists rapid fluctuations.
One consequence for aquatic organisms is that the relatively stable temperature of lakes, oceans and rivers prevents extreme thermal fluctuations, allowing organisms to maintain enzyme function and metabolic processes.
Examiner tips
- Use the word ‘hydrogen bonds’ and explain that energy is needed to break them before temperature rises.
- Show the link between slow temperature change and stable enzyme activity in aquatic life.
Common mistakes
- Failing to mention that water molecules are polar and form hydrogen bonds.
- Confusing the energy required to break bonds with the energy that actually raises temperature.
- Not linking the stable temperature to a specific consequence for aquatic organisms.
Mark scheme (4 marks)
- Water molecules are polar and form hydrogen bonds with each other.
- A large amount of energy is required to increase the kinetic energy / temperature of water because energy must first be used to break / overcome hydrogen bonds before molecules can move faster.
- This means water temperature changes slowly / resists rapid fluctuations in temperature.
- One consequence for aquatic organisms: the relatively stable temperature of lakes / oceans / rivers prevents extreme thermal fluctuations, allowing aquatic organisms to maintain enzyme function / metabolic processes / physiological stability.
Key terms in this question
specific heat capacity · hydrogen bond · aquatic organisms
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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