Which Option Best Describes the Mechanism That Causes a Stoma

Which option best describes the mechanism that causes a stoma to open?

A) K⁺ enters the guard cells and water follows passively, making the cells turgid.
B) K⁺ activates water pumps in the guard cell membrane that make them turgid.
C) K⁺ leaves the guard cells and water follows passively, making the cells flaccid.
D) Loss of K⁺ from guard cells creates positive pressure and expands the guard cells.