A student investigating plant growth cuts off all the leaves from a young plant. Explain why removing all the leaves would reduce the rate of cell elongation in the shoot tips of the plant.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Plants produce auxin in meristem tissue at the shoot tip. Auxin moves down the shoot and causes cell elongation. Auxin production depends on the availability of sugars made during photosynthesis.
Model answer (5 marks)
Leaves are the main site of photosynthesis, so cutting them off stops the plant’s ability to produce glucose. With less glucose available, the meristem at the shoot tip cannot synthesise as much auxin. Auxin is the hormone that stimulates cell elongation in the shoot. Therefore, with reduced auxin production, cells in the shoot tip elongate more slowly, and the overall rate of shoot growth is lowered.
Examiner tips
- Show the causal chain: photosynthesis → glucose → auxin → cell elongation
- Use the exact terms ‘photosynthesis’, ‘glucose’, ‘auxin’, ‘cell elongation’
- Keep the answer concise and directly linked to the marks
Common mistakes
- Confusing photosynthesis with respiration or not mentioning glucose as the key sugar
- Saying auxin is produced in leaves instead of the meristem
- Using vague terms like ‘hormone’ without specifying auxin
Mark scheme (5 marks)
- Leaves are the main site of photosynthesis
- Without leaves, less glucose/sugar is produced by the plant
- Less glucose available means less auxin can be produced/synthesised by meristem tissue
- Auxin stimulates / causes cell elongation in shoot cells
- With less auxin, cells in the shoot tip elongate less / at a reduced rate, so growth is reduced
Key terms in this question
Related
- All Pearson Edexcel A-Level Biology A (9BI0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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