The epidermal cells of guard cell show chloroplast. They have a thin outer wall and thick inner wall and constitute an important functional element of the plant.

Blue light activates proton pumping and stimulates the synthesis of osmotically active organic solutes and maintains the osmoregulation of guard cell.

Guttation is the exudation of xylem sap from the leaves of the plants as the liquid droplets from the tip or edge.

Hydathodes are the specialized pores in the leaves from where exudation of sap takes place by positive hydrostatic root pressure.

Transpiration is a universal process that occurs in all plants. It does not involve root pressure but the water comes out from a plant in the form of water vapour.