A) decreasing the solute concentration in the guard cells
B) increasing the solute concentration in the guard cells
C) weakening of the cell walls of the guard cells to allow them to stretch
D) increasing the water potential in the guard cells.
Correct Answer: B
Solution :
: Opening and closing of stomata is governed by turgor changes in guard cells. During day time, pH of guard cell increases due to \[C{{O}_{2}}\] assimilation by mesophyll and guard cells. This rise in pH causes hydrolysis of starch to form phosphoenol pyruvate. The latter combines with \[C{{O}_{2}}\] in the presence of enzyme PEP case to form oxalic acid which gets changed to malic acid. Malic acid dissociates to \[{{H}^{+}}\] and malate. \[{{H}^{+}}\]ions pass out of guard cells in exchange of \[{{K}^{+}}\]ions which along with malate pass into vacuoles and .increase the osmotic concentration of guard cells. Consequently, they absorb water from nearby epidermal cells and swell up creating a pore .between them.
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