A-LevelBiologyTransport in plants9700/42 · Feb/Mar 2022 · Q107 Marks
10 (a) Fig. 10.1 shows the structure of two guard cells. [Figure 10.1]
- (a)Name the structures labelled A, B and C in Fig. 10.1. A _______ B _______ C _______[3]
- (b)In times of water stress, abscisic acid is released. This results in the closure of stomata to reduce water loss by transpiration. Describe the role of abscisic acid in stomatal closure.[4]
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- [3] A - chloroplast; B - vacuole ; C - cell wall; A cell surface membrane
- [4] any four from: 1 abscisic acid binds to receptors on cell surface membrane (of guard cell); 2 proton pumps are inhibited / AW ; 3 stimulates Ca2+ uptake / opens Ca2+ channels ; 4 Ca2+ acts as second messenger ; 5 K+ diffuses out of the (guard) cell; 6 water potential of (guard) cell increases ; 7 water leaves (guard) cell, by osmosis / down water potential gradient; 8 (guard) cell becomes flaccid / cell volume decreases (so stoma closes);
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