A palisade mesophyll cell and a human cheek cell are both eukaryotic cells. Explain why a palisade mesophyll cell contains chloroplasts and a permanent vacuole, whilst a human cheek cell contains neither of these organelles.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Palisade mesophyll cells are found near the upper surface of a leaf and are specialised for photosynthesis. Human cheek cells are animal cells lining the inside of the mouth.
Model answer (4 marks)
Palisade mesophyll cells are specialised for photosynthesis, so they contain chloroplasts, which house chlorophyll to absorb light energy and carry out the light‑dependent reactions.
They also have a permanent central vacuole that stores cell sap and maintains turgor pressure, which is important for the structural support of plant cells.
Human cheek cells are animal cells that do not perform photosynthesis, so they lack chloroplasts. They also do not require a permanent vacuole to maintain turgidity; animal cells have only small, temporary vacuoles for storage and transport.
They also have a permanent central vacuole that stores cell sap and maintains turgor pressure, which is important for the structural support of plant cells.
Human cheek cells are animal cells that do not perform photosynthesis, so they lack chloroplasts. They also do not require a permanent vacuole to maintain turgidity; animal cells have only small, temporary vacuoles for storage and transport.
Examiner tips
- Mention the function of chloroplasts and vacuoles; link each organelle to the cell’s role; keep the answer concise and use correct terminology.
- Use the word ‘specialised’ or ‘adapted’ to explain why plant cells need chloroplasts.
- Explain that animal cells lack permanent vacuoles because they do not need to maintain turgor pressure.
Common mistakes
- Forgetting to state that chloroplasts contain chlorophyll and are the site of photosynthesis.
- Claiming that animal cells have no vacuoles at all, ignoring the small temporary vacuoles.
- Using vague terms like ‘important’ without linking to the cell’s function.
Mark scheme (4 marks)
- Chloroplasts are the site of photosynthesis / contain chlorophyll to absorb light energy for photosynthesis
- Palisade mesophyll cells need chloroplasts because they are specialised / adapted for photosynthesis, whereas animal/cheek cells do not photosynthesise
- The permanent vacuole stores cell sap / helps maintain the turgidity of the plant cell
- Human cheek cells do not have a permanent vacuole because animal cells do not need to maintain turgidity / only have small temporary vacuoles used for storage and transportation
Key terms in this question
chloroplasts · permanent vacuole · palisade mesophyll · eukaryotic cell
Related
- Revision notes: Cell structures →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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