Explain why a wilting plant that is watered recovers its firm, upright structure.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
A houseplant left without water for several days begins to wilt and its stems become soft and drooping. After watering, the plant gradually becomes firm and upright again.
Model answer (4 marks)
Water enters the root hair cells by osmosis from the soil into the cell sap.
The soil water is a more dilute solution than the cell sap, so water moves across the partially permeable membrane into the cell.
The water fills the central vacuole, increasing the internal pressure (turgor pressure).
The turgid cells press against each other; the rigid cell wall resists expansion, so the plant tissues become firm and the stem stands upright.
The soil water is a more dilute solution than the cell sap, so water moves across the partially permeable membrane into the cell.
The water fills the central vacuole, increasing the internal pressure (turgor pressure).
The turgid cells press against each other; the rigid cell wall resists expansion, so the plant tissues become firm and the stem stands upright.
Examiner tips
- Use the word "osmosis" and mention the soil being more dilute than the cell sap. Show the sequence: water enters root → vacuole fills → turgor pressure → cell wall support. Link the increase in turgor to the plant becoming firm and upright.
Common mistakes
- Forgetting to mention osmosis or the direction of water movement. Describing the plant as simply "getting water" without explaining turgor pressure. Using vague terms like "cell swelling" instead of "turgor pressure".
Mark scheme (4 marks)
- Water enters root hair cells / root cells by osmosis
- Water moves from a more dilute solution (soil water) to a more concentrated solution (cell sap) across a partially permeable membrane
- Water fills the vacuole / enters the vacuole, increasing the pressure inside the cell
- Turgid cells press against each other / cell wall resists expansion, supporting the plant tissues and making the stem firm / upright
Related
- All Pearson Edexcel International GCSE Biology (4BI1) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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