Explain how the structure of a palisade mesophyll cell is adapted for its function in photosynthesis.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Palisade mesophyll cells are long and columnar, so they are arranged perpendicular to the leaf surface, which reduces the distance that light must travel to reach each chloroplast and allows many cells to fit in a given area.
They contain a large number of chloroplasts, giving a high surface‑area‑to‑volume ratio for light absorption and the light‑dependent reactions.
The chloroplasts are positioned near the cell periphery by a large central vacuole, which maximises their exposure to light and to CO₂ diffusing from the intercellular spaces.
Chloroplasts can move or orient themselves within the cell to optimise light capture or to avoid photo‑damage, further enhancing photosynthetic efficiency.
They contain a large number of chloroplasts, giving a high surface‑area‑to‑volume ratio for light absorption and the light‑dependent reactions.
The chloroplasts are positioned near the cell periphery by a large central vacuole, which maximises their exposure to light and to CO₂ diffusing from the intercellular spaces.
Chloroplasts can move or orient themselves within the cell to optimise light capture or to avoid photo‑damage, further enhancing photosynthetic efficiency.
Examiner tips
- Use the word ‘adapted’ and link structure to function; mention light absorption, chloroplast number, orientation and cell shape.
- Show the four points in separate sentences or bullet‑style points to match the 4 marks.
Common mistakes
- Confusing palisade cells with spongy mesophyll; describing only one feature; omitting chloroplast movement or the role of the vacuole.
Mark scheme (4 marks)
- Palisade mesophyll cells contain a large number of chloroplasts, increasing the surface area/volume available for light absorption and the light-dependent reactions.
- Chloroplasts can move/are positioned along the cell to optimise light capture or avoid photo-damage (chloroplast movement/orientation).
- The elongated/columnar shape of palisade cells means they are arranged perpendicular to the leaf surface, reducing the path length for light to reach each chloroplast and packing more cells per unit area.
- A large central vacuole pushes the chloroplasts to the periphery of the cell / towards the cell membrane, maximising exposure to CO₂ and light.
Key terms in this question
palisade mesophyll cell · photosynthesis
Related
- All IB DP Biology Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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