Explain why a plant begins to wilt when the rate of transpiration is greater than the rate of water uptake by the roots.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
A plant wilts when transpiration exceeds water uptake because more water leaves the plant than enters. The excess loss causes water to move out of the cells by osmosis, reducing the water content of the cells. As a result, turgor pressure falls and the cells lose turgidity. Without sufficient turgor, the non‑woody tissues can no longer stay rigid, so the plant wilts.
Examiner tips
- Use the terms ‘transpiration’, ‘water uptake’, ‘osmosis’, ‘turgor pressure’ and ‘turgidity’.
- Show the causal chain: loss of water → osmotic loss → reduced turgor → wilting.
- Keep the answer concise and directly linked to the marks scheme.
Common mistakes
- Confusing transpiration with evaporation; not mentioning osmosis; using vague phrases like ‘water loss’ without linking to turgor.
Mark scheme (4 marks)
- Excess water is lost from the plant via transpiration / more water leaves the plant than enters
- Water moves out of the cells (by osmosis)
- Turgor pressure / turgidity of cells decreases
- The cells can no longer support the non-woody structures of the plant, causing wilting
Key terms in this question
Related
- All Cambridge International IGCSE Biology (0610) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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