What closes the stomata and how do they do it?
By controlling how much water goes into its vacuole affecting the cell's turgidity (thereby affecting its shape). It does this by controlling salt concentration (potassium ion) inside cell. The .....
The potassium ion concentration itself is a response to the movement of proton (hydrogen ion) that affects the electric potential across cell membrane. Both potassium ion and proton have their corresponding transporter (transmembrane) protein that does the job. Potassium ion transporter protein is triggered by proton electric potential difference. Meanwhile, proton transporter is a response to light.