Fig. 1 shows a prickly pear cactus growing in a dry botanical garden. The plant has a thick green stem, spines instead of broad leaves and a waxy outer surf...
Question 1 Report
Fig. 1 shows a prickly pear cactus growing in a dry botanical garden. The plant has a thick green stem, spines instead of broad leaves and a waxy outer surface. At night, pores in the stem can open to allow carbon dioxide to enter. During the day the pores are mostly closed, but the plant can still use light energy to make food. This reduces water loss in the hot, dry conditions.
(a) Name the process that uses carbon dioxide and light energy to make food in this plant. [1]
(b) Describe two features in Fig. 1 that reduce water loss. [2]
(c) Explain why carbon dioxide is needed for the cactus to make glucose. [1]
(d) Suggest two ways in which a cactus can use the glucose made by photosynthesis. [2]
Answer Details
(a) The process is photosynthesis. [1 mark]
(b) Two water-loss-reducing features are:
- Spines have a much smaller surface area than broad leaves, reducing evaporation. [1 mark]
- A waxy outer surface reduces evaporation of water. [1 mark]
A thick stem that stores water, and pores opening mainly at night, are also acceptable adaptations. At night temperatures are lower, so opening pores then reduces water loss.
(c) Carbon dioxide supplies the carbon atoms from which glucose is made in photosynthesis. [1 mark]
(d) Any two uses of glucose:
- used in respiration to release energy; [1 mark]
- converted to starch for storage; [1 mark]
- used to make cellulose for cell walls; [1 mark]
- converted into lipids or proteins when suitable additional substances are available. [1 mark]
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