Green plants make their own food. They use light energy from the Sun. This happens mostly in the leaves. Leaf cells hold a green pigment. It is called chlor...
Question 1 Report
Green plants make their own food. They use light energy from the Sun. This happens mostly in the leaves. Leaf cells hold a green pigment. It is called chlorophyll. In the leaf the plant takes in carbon dioxide. It takes up water from the soil. It uses light to change these into glucose and oxygen. The oxygen goes into the air. The glucose is used or stored as starch. A gardener grew tomatoes in a greenhouse. They grew a bigger crop than plants outside. The gardener thought the warmth and carbon dioxide helped. A student used limiting factors to explain this.
(a) Write the word equation for photosynthesis. [2]
(b) State the part of the plant cell in which photosynthesis takes place. [1]
(c) State two uses the plant makes of the glucose produced in photosynthesis. [2]
(d) Explain, using the idea of limiting factors, why the tomato plants in the warm, carbon-dioxide-rich greenhouse grew better. [4]
(e) Suggest one other factor the gardener could increase to raise the rate of photosynthesis further. [1]
Answer Details
This question tests the photosynthesis equation, where it happens, the fate of glucose, and how limiting factors control the rate.
(a) The word equation for photosynthesis [2] (1 mark for the correct reactants and glucose, 1 mark for oxygen):
carbon dioxide + water \(\xrightarrow{\text{light, chlorophyll}}\) glucose + oxygen
Light energy and chlorophyll are the conditions that drive the reaction and are shown above the arrow, not as raw materials.
(b) Photosynthesis takes place in the chloroplast, which contains the chlorophyll that absorbs light. [1]
(c) Any two uses of the glucose (1 mark each) [2]: used in respiration to release energy; converted to starch for storage; or used to make cellulose, sucrose, or (with nitrogen) amino acids and proteins.
(d) Using limiting factors [4]: the rate of photosynthesis is limited by whichever factor is in shortest supply [1]. Adding more carbon dioxide supplies more raw material for the reaction [1], and the extra warmth increases the rate of the enzyme-controlled reactions [1], so photosynthesis proceeds faster and more glucose is made for growth, giving a bigger crop. [1]
(e) The gardener could increase the light intensity to raise the rate of photosynthesis further. [1]
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