A farmer keeps her tomato plants in a greenhouse. During winter, the farmer notices that the rate of photosynthesis in her tomato plants is much lower than in summer. Explain why the rate of photosynthesis is lower in winter, and describe TWO ways the farmer could increase the rate of photosynthesis in her greenhouse during winter.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
During winter the rate of photosynthesis is lower because (1) light intensity is reduced – there are fewer daylight hours and the sun is lower in the sky, so light becomes a limiting factor; (2) temperature is lower, which slows the enzyme‑mediated reactions of the Calvin cycle, making temperature a limiting factor.
To increase the rate in the greenhouse the farmer could:
1. Install artificial lighting to raise light intensity.
2. Heat the greenhouse to raise temperature, removing the temperature limitation.
To increase the rate in the greenhouse the farmer could:
1. Install artificial lighting to raise light intensity.
2. Heat the greenhouse to raise temperature, removing the temperature limitation.
Examiner tips
- Use the word ‘limiting factor’ when linking light/temperature to rate; include both points for full marks.
- Show the two practical solutions clearly, using the exact wording from the mark scheme (artificial lighting, heating).
Common mistakes
- Failing to mention both light and temperature as limiting factors; only citing one. Not specifying the solutions as ‘artificial lighting’ and ‘heating’ – using vague terms like ‘more light’ or ‘warm up the room’ may lose marks.
Mark scheme (4 marks)
- Light intensity is lower in winter (fewer daylight hours / less sunlight), so light is a limiting factor that reduces the rate of photosynthesis.
- Temperature is lower in winter, so temperature acts as a limiting factor reducing the rate of photosynthesis.
- The farmer could add artificial lighting to the greenhouse to increase light intensity.
- The farmer could heat the greenhouse to increase temperature, removing temperature as a limiting factor.
Key terms in this question
Related
- Revision notes: Photosynthesis →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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