Question

What causes the opening and closing of guard cells of stomata during transpiration?

Answer 1

The process of water movement through a plant and the evaporation from aerial parts is called transpiration. The transpiration takes place through the stomata of the leaves.

Complete Answer:

The stomata are the tiny pores present on the surface of leaves.
They help in exchange of gases.
Each stoma has guard cells.
The guard cells are specialized plant cells present in the epidermis of leaves, stems.
The change in the turgidity of the guard cells causes their opening and closing.
The guard cells are responsible to regulate the rate of transpiration by opening and closing the stomata.
The guard cells are produced in pairs with a gap between them called as stomatal pore.
The guard cells have thick cuticles on the pore side and thin opposite to it.
During the opening of stomata the turgidity of guard cells increases. The outer walls bulge and the inner walls become crescent shaped.
During closing of the stomata the guard cells lose their turgidity. The outer and inner walls retain original shapes.
Cell walls of varying thickness and differently oriented cellulose microfibers are present in the guard cells which cause them to bend outward when they are turgid and cause stomata to open.

Note: The opening and closing of the stomatal pore is regulated by turgor pressure of two guard cells. The turgor pressure depends on the movements of large quantities of ions and sugars into and out of guard cells.