Explain how water moves from the soil into the xylem of a plant root and then up through the stem to the leaves.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Water is transported from the soil to the leaves of a flowering plant through a continuous pathway involving osmosis and the xylem vessels.
Model answer (4 marks)
1. Water enters root hair cells from the soil by osmosis, moving from a more dilute solution (soil water) to a more concentrated solution (root hair cell) across a partially permeable membrane.
2. It then passes from cell to cell across the root cortex by osmosis, moving towards the xylem.
3. Water travels up the xylem vessels from roots to leaves, with the xylem transporting water through the stem.
4. Water is lost from the leaves by transpiration, and the evaporation of water pulls water up the xylem.
2. It then passes from cell to cell across the root cortex by osmosis, moving towards the xylem.
3. Water travels up the xylem vessels from roots to leaves, with the xylem transporting water through the stem.
4. Water is lost from the leaves by transpiration, and the evaporation of water pulls water up the xylem.
Examiner tips
- Use the word "osmosis" for the movement into root hairs and through the cortex. Mention the xylem as the continuous pathway. Explain that transpiration creates a negative pressure that pulls water up. Keep each point brief and directly linked to the mark scheme.
Common mistakes
- Confusing diffusion with osmosis. Forgetting to mention the xylem as the transport tissue. Not linking transpiration to the upward pull of water.
Mark scheme (4 marks)
- Water enters root hair cells from the soil by osmosis / water moves from a more dilute solution (soil water) to a more concentrated solution (root hair cell) across a partially permeable membrane
- Water passes from cell to cell across the root cortex by osmosis, moving towards the xylem
- Water travels up the xylem vessels from roots to leaves / xylem transports water through the stem
- Water is lost from the leaves by transpiration / evaporation of water from the leaves pulls water up the xylem
Key terms in this question
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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