A farmer notices that tomato plants grown in a greenhouse produce more fruit when the greenhouse is heated and the carbon dioxide concentration inside is increased. Explain how increasing the temperature and increasing the carbon dioxide concentration inside the greenhouse each help to increase the rate of photosynthesis in the tomato plants.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Tomato plants are grown commercially in heated greenhouses where carbon dioxide is pumped in artificially. Growers do this to maximise the yield of tomatoes produced.
Model answer (5 marks)
1. Photosynthesis requires carbon dioxide as a reactant.
2. Increasing the CO₂ concentration inside the greenhouse supplies more of this reactant, so the rate of photosynthesis rises.
3. Photosynthesis is an endothermic reaction that occurs in chloroplasts and is carried out by enzymes.
4. Raising the temperature increases enzyme activity (up to the optimum temperature), which accelerates the photosynthetic reactions.
5. The higher rate of photosynthesis produces more glucose, giving the plant more energy and building material for growth, which results in a greater fruit yield.
2. Increasing the CO₂ concentration inside the greenhouse supplies more of this reactant, so the rate of photosynthesis rises.
3. Photosynthesis is an endothermic reaction that occurs in chloroplasts and is carried out by enzymes.
4. Raising the temperature increases enzyme activity (up to the optimum temperature), which accelerates the photosynthetic reactions.
5. The higher rate of photosynthesis produces more glucose, giving the plant more energy and building material for growth, which results in a greater fruit yield.
Examiner tips
- Use the exact terms: CO₂, chloroplasts, enzymes, endothermic, optimum temperature.
- Show the causal chain: CO₂ → more reactant → higher rate; heat → enzyme activity → higher rate; higher rate → more glucose → more fruit.
Common mistakes
- Confusing photosynthesis with respiration; writing ‘photosynthesis uses oxygen’ instead of CO₂.
- Failing to mention that the reaction is endothermic or that enzymes are involved.
- Not linking the increased glucose production to the increased fruit yield.
Mark scheme (5 marks)
- Photosynthesis requires carbon dioxide (as a reactant)
- Increasing carbon dioxide concentration increases the rate of photosynthesis (because more reactant is available)
- Photosynthesis is an endothermic reaction that takes place in the chloroplasts and involves enzymes
- Increasing temperature increases the rate of enzyme activity (up to the optimum temperature), so the rate of photosynthesis increases
- More glucose is produced (by photosynthesis), providing more energy/materials for growth, leading to greater fruit yield
Key terms in this question
photosynthesis · carbon dioxide · rate of photosynthesis
Related
- All OCR A-Level Biology B — Advancing Biology (H422) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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