Question 1
Which change in a glasshouse is most likely to increase the rate of photosynthesis if carbon dioxide is the limiting factor?
- Increasing the carbon dioxide concentration
- Decreasing the temperature
- Shading the glass to reduce the light
- Adding more oxygen
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Answer: A (1)
Question 2
State two ways in which a polythene tunnel can increase the yield of a crop.
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- traps heat / keeps plants warm so faster growth (1)
- protects from pests / wind / frost / heavy rain (1)
- allow lets the growing season be extended (1)
- Max 2
Question 3
Explain how adding fertiliser to the soil can increase the yield of a crop.
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- fertilisers contain mineral ions / nitrates (1)
- nitrate is used to make protein (1)
- so plants grow faster / bigger, giving a higher yield (1)
- ignore plant food
Question 4
Farmers can use a pesticide or biological control to reduce the number of aphids on a crop. Give two advantages and two disadvantages of using a pesticide instead of biological control.
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- advantage: kills pests quickly / more effective (1)
- advantage: easy to apply over a large area (1)
- disadvantage: kills non-target organisms / harmless insects (1)
- disadvantage: pests may become resistant / may build up in food chains / pollute water (1)
- allow other correct points
Question 5
The table shows the mean mass of tomatoes grown on one plant in a glasshouse with and without extra carbon dioxide. Calculate the percentage increase in mass with extra carbon dioxide.
| Carbon dioxide | Mass of tomatoes per plant in kg |
|---|---|
| Normal air | 4.0 |
| Extra carbon dioxide | 5.0 |
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- increase = 5.0 − 4.0 = 1.0 kg (1)
- (1.0 ÷ 4.0) × 100 (1)
- 25% (1)
- correct answer with no working gains 3 marks
- reject (1.0 ÷ 5.0) × 100 = 20%
Question 6
A farmer wants to grow a large crop of lettuces. Describe and explain how the farmer could use a glasshouse and other methods to increase the yield.
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| Level | Marks | What the answer does |
|---|---|---|
| 3 | 5–6 | Detailed description and explanation of at least three methods, linking each to a clear reason for increased yield, with correct use of terms such as photosynthesis, limiting factor, mineral ions and pests. |
| 2 | 3–4 | Describes at least two methods and gives some explanation of how they increase yield, with some use of scientific terms. |
| 1 | 1–2 | Identifies one or two methods with little or no explanation. |
Indicative content
- glasshouse traps heat; higher temperature raises the rate of photosynthesis (enzyme activity) up to the optimum
- added carbon dioxide increases photosynthesis if limiting, so more glucose for growth
- extra light lengthens photosynthesis time
- protection from wind, frost and pests reduces crop loss
- fertiliser supplies nitrates for protein, so faster growth
- pesticide or biological control reduces damage by pests, so less crop is eaten
- a limiting factor must be dealt with first, or extra of another factor has no effect