Explain why water moves from the soil into a root hair cell and then continues to move up through the plant to the leaves.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Water moves into the root hair cell by osmosis because the cell has a lower water potential (higher solute concentration) than the surrounding soil solution, so water enters.
The loss of water from the leaves by transpiration through the stomata creates a continuous transpiration stream and tension that pulls water up through the xylem to the leaves.
The loss of water from the leaves by transpiration through the stomata creates a continuous transpiration stream and tension that pulls water up through the xylem to the leaves.
Examiner tips
- Use the word ‘osmosis’ and mention lower water potential in the root hair cell; link transpiration to a continuous tension in the xylem; keep answer concise to fit 4 marks.
Common mistakes
- Forgetting to state that the root hair cell has a lower water potential; confusing transpiration with evaporation; not mentioning the continuous tension in the xylem.
Mark scheme (4 marks)
- Water moves into the root hair cell by osmosis
- The root hair cell has a lower water potential / higher solute concentration than the soil solution, so water enters
- Water is lost from leaves by transpiration / evaporation through the stomata
- This creates a continuous transpiration stream / tension that pulls water up through the xylem
Related
- All Eduqas GCSE Biology revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →