How do potassium ions affect the opening of stoma?

Potassium ions play a crucial role in the mechanism that regulates the opening of stomata, which are small openings on the surface of leaves. When potassium ions are actively transported into the guard cells, they cause an increase in the concentration of solutes within these cells. This increase in solute concentration leads to osmotic movement of water into the guard cells from the surrounding epidermal cells.

As water enters the guard cells, their turgor pressure rises, causing the cells to swell and effectively bend apart at the stomatal pore. This process allows the stomata to open, facilitating gas exchange necessary for photosynthesis and respiration. Therefore, the correct answer reflects the physiological process whereby potassium ions enhance the solution concentration in the guard cells, prompting water influx that is critical for stomatal opening.