A horticulturist photographs a cactus growing in a dry botanical garden. Fig. 1 shows the structure of the plant. The garden has very little rainfall for se...
Question 1 Report
A horticulturist photographs a cactus growing in a dry botanical garden. Fig. 1 shows the structure of the plant. The garden has very little rainfall for several months each year, so conserving water is important for the cactus cells.
(a) Describe two visible features of the cactus in Fig. 1 that help it survive in a dry habitat. [4]
(b) Explain how each of these features reduces water loss or improves water supply to the plant body. [4]
(c) State the name of the process by which water vapour leaves a plant leaf or stem. [1]
(d) Suggest why a cactus with a large leaf surface area would be less likely to survive in this habitat. [2]
Answer Details
(a) Two visible xerophytic features are leaves reduced to spines and a thick, fleshy green stem. Other acceptable visible features are wide-spreading shallow roots and a waxy outer surface. For each feature, description gains credit. [4]
(b) Spines have a small surface area, reducing transpiration or evaporation. The fleshy stem stores water. Wide shallow roots rapidly absorb water from a large area after rain, and a waxy layer reduces evaporation. Explain the two features selected in part (a). [4]
(c) Water vapour leaves a plant by transpiration. [1]
(d) A large leaf surface area exposes more cells to the air. More water would then be lost by transpiration, making survival in a dry habitat less likely. [2]
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