Describe the roles of the xylem and phloem in a leaf, and explain why both tissues are necessary for photosynthesis to continue.

Cambridge International IGCSE Biology (0610) — 6.2 Leaf structure · Describe · 4 marks · View as Markdown

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

Model answer (4 marks)

Xylem carries water and dissolved minerals from the stem to the leaf, providing the water needed for photosynthesis.
Phloem carries the sugars (sucrose, glucose) produced in the leaf to other parts of the plant.
The transport of water by xylem supplies the reactant for the light‑dependent and Calvin‑cycle reactions.
The removal of sugars by phloem prevents their accumulation, keeping the photosynthetic machinery operating efficiently.

Examiner tips

  • Use the terms xylem and phloem explicitly. Show the flow of water to the leaf and sugars away from it. Explain that water is a reactant and sugar removal keeps photosynthesis running.

Common mistakes

  • Confusing xylem with phloem or vice versa. Forgetting to mention that sugars are removed, not just produced. Using vague language like "transport" without specifying direction or purpose.

Mark scheme (4 marks)

  1. Xylem transports water (and dissolved minerals) to the leaf
  2. Water is a raw material / reactant needed for photosynthesis
  3. Phloem transports sugars (sucrose / glucose) away from the leaf
  4. Removal of sugars by phloem prevents sugar accumulation / allows photosynthesis to continue

Key terms in this question

xylem · phloem · photosynthesis

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