Explain how the properties of water are important to plants living in environments that experience high temperatures.

AQA A-Level Biology (7402) — 3.1.7 Water · Explain · 5 marks · View as Markdown

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

Plants lose water from their leaves by evaporation. This process helps to cool the plant. Water is also used in many other ways by plants.

Model answer (5 marks)

Water has a high latent heat of vaporisation, so when it evaporates from leaf surfaces it removes a large amount of heat energy, cooling the plant.
Water is a good solvent; many minerals, sugars and other solutes dissolve in it.
This allows dissolved nutrients to be transported through the xylem and phloem to all parts of the plant.
Water is also a reactant in photosynthesis (CO₂ + H₂O → C₆H₁₂O₆ + O₂) and in many other cellular reactions.
Thus, the physical and chemical properties of water enable plants to dissipate heat, transport nutrients and carry out essential metabolic processes in hot environments.

Examiner tips

  • Mention latent heat of vaporisation first to secure the cooling point. Include transport of nutrients via xylem/phloem to cover the solvent point. State photosynthesis as a key reaction to hit the reactant point. Use UK spelling and correct terminology (latent heat, xylem, phloem).

Common mistakes

  • Forgetting to mention the latent heat of vaporisation. Using ‘water evaporates’ without linking it to heat removal. Mixing up xylem and phloem functions or omitting the solvent role of water.

Mark scheme (5 marks)

  1. Water has a high latent heat of vaporisation
  2. So evaporation of water from leaves removes a large amount of heat energy, cooling the plant
  3. Water is a good solvent / many substances dissolve in water
  4. So dissolved minerals / nutrients / sugars can be transported around the plant (in the xylem / phloem)
  5. Water is a reactant in photosynthesis / used in chemical reactions inside cells

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