Explain why the leaves of most plants are broad and flat, and contain chlorophyll, in terms of how these features affect the rate of photosynthesis.

AQA A-Level Biology (7402) — 3.5.1 Photosynthesis · Explain · 5 marks · View as Markdown

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

Model answer (5 marks)

Broad and flat leaves give a large surface area, allowing more light to be intercepted.
A larger area means more photons reach chlorophyll molecules.
Chlorophyll absorbs this light energy.
The absorbed light energy drives the light‑dependent reactions, converting CO₂ and H₂O into glucose and O₂.
Thus the leaf shape and chlorophyll content increase the rate of photosynthesis.

Examiner tips

  • Use the word ‘broad and flat’ to link to surface area. Explain the chain: area → light absorption → chlorophyll → energy conversion. Show the final product (glucose, O₂) to demonstrate understanding of the light‑dependent process.
  • common_mistakes
  • :
  • Confusing leaf shape with colour or texture. Forgetting to mention chlorophyll’s role in absorbing light. Not linking light absorption to the production of glucose and oxygen.

Mark scheme (5 marks)

  1. Broad and flat leaves provide a large surface area
  2. Large surface area allows more light to be absorbed / intercepted
  3. More light energy available increases the rate of photosynthesis
  4. Chlorophyll absorbs light energy (for photosynthesis)
  5. Light energy is used to convert carbon dioxide and water into glucose (and oxygen) / light energy drives photosynthesis

Key terms in this question

photosynthesis · chlorophyll

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