Explain how a cactus plant is adapted to survive in a hot desert environment.

AQA GCSE Biology (8461) — 4.7.1 Adaptations, interdependence and competition · Explain · 4 marks · View as Markdown

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

Cacti are plants that live in hot desert environments where water is scarce and temperatures are extreme.

Model answer (4 marks)

A cactus has a thick, swollen stem that stores water, allowing it to survive long periods of drought.
Its spines replace leaves, reducing the surface area from which water can be lost by transpiration.
The plant has an extensive root system, either spreading wide or growing deep, to maximise water uptake from the soil.
Its pale or waxy cuticle reflects sunlight, lowering leaf temperature and further reducing water loss.

Examiner tips

  • Use the exact terms: "thick stem", "spines", "extensive root system", "pale/waxy cuticle". Show the link between each adaptation and the desert environment. Keep the answer concise – one sentence per point – to fit the 4 marks.

Common mistakes

  • Confusing spines with leaves – remember spines are modified leaves. Forgetting to mention the stem’s water‑storage function. Using vague phrases like "good adaptation" without specifying the mechanism.

Mark scheme (4 marks)

  1. Thick/swollen stem (or fleshy stem) stores water
  2. Spines instead of leaves reduce water loss (by transpiration / reducing surface area)
  3. Extensive/wide-spreading or deep root system to absorb as much water as possible
  4. Pale/light-coloured or waxy surface (cuticle) reflects sunlight / reduces overheating / reduces water loss

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