A gardener adds a large amount of salt fertiliser to the soil around a healthy plant. The following day, the plant shows signs of wilting. Explain why the plant wilts after salt is added to the soil.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Adding salt to the soil lowers the soil water potential, making the soil solution more concentrated.
Water then moves out of the root hair cells into the soil by osmosis, following the water potential gradient.
This reduces the amount of water taken up by the roots.
As the cells lose water, turgor pressure falls, causing the plant to wilt.
Water then moves out of the root hair cells into the soil by osmosis, following the water potential gradient.
This reduces the amount of water taken up by the roots.
As the cells lose water, turgor pressure falls, causing the plant to wilt.
Examiner tips
- Use the term ‘water potential’ and ‘osmosis’. Show the direction of water movement. Explain the link between reduced uptake and loss of turgor. Keep the answer concise, covering all four points.
Common mistakes
- Saying the plant wilts because of ‘high salt concentration’ without mentioning water potential. Forgetting to state that water moves out of the cells. Using vague terms like ‘drying out’ instead of ‘loss of turgor’.
Mark scheme (4 marks)
- Adding salt to the soil lowers the water potential of the soil (makes the soil solution more concentrated)
- Water moves out of the root hair cells into the soil by osmosis (water moves down a water potential gradient)
- Less water is taken up into the plant / water uptake by roots decreases
- Cells lose water and turgor pressure decreases, 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 →