A) potassium
B) sodium
C) sulphur
D) phosphorus
Correct Answer: A
Solution :
According to ATP-driven proton \[({{H}^{+}})-{{K}^{+}}\] exchange pump mechanism in guard cells, proposed by Levitt (1974), a rise in pH during day time causes hydrolysis of starch to form organic acid (PEP) which combines with available \[C{{O}_{2}}\] to produce malic acid that dissociates to produce H+ and malate. The protons \[({{H}^{+}})\] are pumped out from the guard cells into the subsidiary cells and in exchange K+ ions are pumped into them from, the adjustment subsidiary cells. This exchange of \[{{H}^{+}}\] and \[{{K}^{+}}\] ions is followed by entry of \[C{{l}^{-}}\] anions into the guard cells with the help of c-AMP, ATP and cytokinins. \[{{K}^{+}}\]are immediately combines with malate and increase the osmotic concentration of the guard cells. As a result guard cells absorb water from the nearby epidermal (subsidiary) cells, swell up and leads to opening of stomata.
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