Explain why the palisade mesophyll tissue is well suited to carry out photosynthesis in a leaf.

Pearson Edexcel International GCSE Biology (4BI1) — 2.5 Nutrition: flowering plants · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Palisade mesophyll cells contain many chloroplasts, the site of photosynthesis.
They are located at the top of the leaf, receiving maximum light.
The cells are column‑shaped and tightly packed, increasing chloroplast number per unit area and maximising light absorption.
Carbon dioxide diffuses in from the air spaces and water moves in from the xylem, providing the substrates for photosynthesis.

Examiner tips

  • Use the exact terms: palisade mesophyll, chloroplasts, column‑shaped, tightly packed, CO₂ diffusion, xylem.
  • Show the link between cell structure and light absorption. Mention both light and CO₂ supply as reasons for suitability.

Common mistakes

  • Confusing palisade with spongy mesophyll. Omitting the role of CO₂ diffusion or water supply. Using vague phrases like "good for photosynthesis" without detail.

Mark scheme (4 marks)

  1. Palisade mesophyll cells contain many chloroplasts / chloroplasts are the site of photosynthesis
  2. Palisade mesophyll is located at the top / upper surface of the leaf to receive maximum light
  3. The cells are column-shaped / tightly packed, increasing the number of chloroplasts per unit area / maximising light absorption
  4. Carbon dioxide / water can diffuse into the cells for photosynthesis (e.g. CO₂ diffuses in from air spaces / water moves in from xylem)

Key terms in this question

palisade mesophyll · photosynthesis

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