A farmer grows crops in a large greenhouse. During winter, the farmer notices that the crops grow much more slowly than in summer. Explain how two different limiting factors could be responsible for the slower growth of crops in the greenhouse during winter.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Greenhouses are used to grow crops throughout the year. However, crop growth rates can vary significantly between seasons even inside a greenhouse.
Model answer (4 marks)
Light intensity is a limiting factor in winter. Less light reaches the leaves, so chlorophyll absorbs less energy, reducing the rate of photosynthesis and therefore plant growth.
Temperature is a second limiting factor. At lower temperatures the enzymes that drive photosynthesis work more slowly, which lowers the rate of photosynthesis and glucose production, slowing crop growth.
Temperature is a second limiting factor. At lower temperatures the enzymes that drive photosynthesis work more slowly, which lowers the rate of photosynthesis and glucose production, slowing crop growth.
Examiner tips
- Use the word ‘limiting factor’ and identify light and temperature. Explain the effect of each on photosynthesis. Show cause‑effect links (less light → less energy absorbed; low temperature → slower enzyme activity).
Common mistakes
- Confusing light intensity with light quality. Failing to explain the biochemical effect of temperature on enzymes. Using vague phrases like ‘less growth’ without linking to photosynthesis.
Mark scheme (4 marks)
- Identifies light intensity / light as a limiting factor in winter
- Explains how reduced light limits photosynthesis / growth — less light energy is absorbed by chlorophyll so the rate of photosynthesis is reduced
- Identifies temperature as a second limiting factor in winter
- Explains how lower temperature limits photosynthesis / growth — enzymes involved in photosynthesis work more slowly at lower temperatures, reducing the rate of photosynthesis and glucose production
Key terms in this question
Related
- Revision notes: Photosynthesis →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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