The diagram shows a greenhouse bench used for growing lettuce plants. A sensor switches on a lamp when light intensity is low. Carbon dioxide can be release...
Question 1 Report
The diagram shows a greenhouse bench used for growing lettuce plants. A sensor switches on a lamp when light intensity is low. Carbon dioxide can be released from a cylinder, and fans move air around the leaves. The grower wants rapid growth but also wants to avoid wasting energy.
(a) Name the process in plants that uses carbon dioxide and light energy. [1]
(b) Describe two ways shown in Fig. 1 that could increase the rate of this process. [2]
(c) Explain why the fan may improve lettuce growth even though it does not supply carbon dioxide. [2]
(d) Use knowledge of limiting factors to explain why adding more carbon dioxide may not always increase crop yield. [2]
(e) Suggest two measurements the grower should make when comparing the growth of lettuces in two greenhouse treatments. [2]
Answer Details
(a) The process using carbon dioxide and light energy is photosynthesis. [1]
(b) The lamp provides more light [1], and the carbon dioxide cylinder increases carbon dioxide concentration [1]. Both can increase photosynthesis when they are limiting factors. [2]
(c) The fan mixes air around the leaves and replaces air that has become depleted in carbon dioxide [1]. This maintains diffusion of carbon dioxide into leaf cells [1], supporting photosynthesis and growth. [2]
(d) Another factor, such as light intensity, temperature, water or mineral ions, may be limiting [1]. Once carbon dioxide is no longer limiting, extra carbon dioxide cannot increase photosynthesis or crop yield [1]. [2]
(e) Any two valid measurements gain [2]: fresh mass or dry mass; leaf area; number or mass of harvested lettuce heads; or increase in height over a stated time.
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