Explain why a plant wilts when the soil around its roots dries out, referring to the roles of root hair cells and guard cells in your answer.

Edexcel GCSE Biology (1BI0) — 6.2 Transport in plants · Explain · 4 marks · View as Markdown

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

During a prolonged dry spell, the soil around a potted plant loses most of its water. Within a few days the plant's leaves and stem begin to droop.

Model answer (4 marks)

Root hair cells can no longer absorb water from the dry soil, so less water enters the plant.
Water is still lost from leaves by transpiration, so the plant loses more water than it gains.
Guard cells lose water and become flaccid, causing stomata to close (to reduce further water loss).
Cells throughout the plant lose water / become flaccid, reducing turgor pressure, so the plant wilts / droops.

Examiner tips

Use the exact terms: root hair cells, guard cells, turgor pressure, stomata.
Show the causal chain: dry soil → less absorption → more transpiration loss → guard cell shrinkage → stomata close → loss of turgor → wilting.
Keep each point short and directly linked to the mark scheme points.

Common mistakes

Confusing wilting with leaf drop; not mentioning guard cells or stomata.
Using vague terms like ‘water loss’ without linking to transpiration or turgor.
Writing a long paragraph instead of clear, separate points.

Mark scheme (4 marks)

Root hair cells can no longer absorb water from the dry soil, so less water enters the plant
Water is still lost from leaves by transpiration, so the plant loses more water than it gains
Guard cells lose water and become flaccid, causing stomata to close (to reduce further water loss)
Cells throughout the plant lose water / become flaccid, reducing turgor pressure, so the plant wilts / droops

Key terms in this question

root hair cells · guard cells