Explain how the structure of xylem vessels makes them well adapted for transporting water and minerals from the roots to the leaves of a plant.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Plants need to move water and dissolved minerals from the soil up to their leaves. Xylem vessels are specialised plant cells responsible for this transport.
Model answer (4 marks)
Xylem vessels are hollow, providing an unobstructed pathway for water to move.
Lignin in the vessel walls gives them strength, so they do not collapse under the tension created by transpiration.
The vessels are joined end‑to‑end, forming long continuous tubes that allow water to travel from roots to leaves.
Water and dissolved minerals move passively by mass flow (cohesion‑tension) up the concentration gradient, so no energy is required.
Lignin in the vessel walls gives them strength, so they do not collapse under the tension created by transpiration.
The vessels are joined end‑to‑end, forming long continuous tubes that allow water to travel from roots to leaves.
Water and dissolved minerals move passively by mass flow (cohesion‑tension) up the concentration gradient, so no energy is required.
Examiner tips
- Use the exact terms ‘hollow’, ‘lignin’, ‘continuous tubes’ and ‘mass flow’ as the mark scheme expects.
- Show the link between the structure (hollow, lignified, continuous) and the function (passive transport).
Common mistakes
- Confusing xylem with phloem or mentioning active transport.
- Omitting the role of lignin or the continuous nature of the vessels.
Mark scheme (4 marks)
- Xylem vessels are hollow/have no living contents, providing an unobstructed pathway for water movement
- Lignin strengthens the xylem vessel walls, preventing them from collapsing under pressure
- Xylem vessels are joined end to end, forming long continuous tubes that allow water to travel from roots to leaves
- Water and minerals move by diffusion/osmosis/mass flow up the concentration gradient, and the structure allows this passive movement without requiring energy
Key terms in this question
Related
- Revision notes: Supplying the cell →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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