Question

The turgidity of the guard cells is maintained by
(a) OP
(b) TP
(c) WP
(d) DP

Answer 1

This is the minimum pressure that is required to be applied to a solution to prevent the backflow or inward flow of its pure solvent across the semipermeable membrane. This is the tendency of taking in a pure solvent by a solution with the help of the process of osmosis.

Complete answer:
Osmotic pressure (OP) is responsible for maintaining the turgidity of the guard cells. Turgidity is the point at which the membrane of the cell pushes against the cell wall, this takes place when the turgor pressure is high. Similarly, when the turgor pressure is low in the cell membrane it will become flaccid. In plants when the surrounding solution of cell sap becomes less negative as compared to it, this will lead to the movement of water from the region of less negative or high water potential to the region of more negative or low water potential. This movement of water inside the guard cells is made possible with the help of osmotic pressure which creates the turgor pressure (TP) inside the guard cells. This turgor pressure is made balanced by wall pressure (WP). So, we can say that it is osmotic pressure that is responsible for the creation of turgor pressure and wall pressure in the guard cells.

Additional Information:
-The opening and closing of the stomatal pore takes place due to the changes in the turgor pressure of the two guard cells.
-The turgor pressure of guard cells is mainly controlled by the movements of large quantities of ions and sugars from inside and outside of the guard cells.
-Guard cells have cell walls with different thicknesses at various places and differently oriented cellulose microfibers which make them bend outward when they are turgid, this finally results in the opening of the stomata.
-Stomata closes when there is an osmotic loss of water, which is mainly because of the loss of potassium ions from neighboring cells.
-Guard cells are specialized plant cells present in the epidermis of leaves, stems, and other organs from where the exchange of gases is controlled in the plants.
-Guard cells are produced in pairs with a gap between them which forms a pore called a stomatal pore.

So, the correct answer is, ‘osmotic pressure (OP)’.

Note:
-Turgidity is the point at which the cell membrane starts pushing itself against the cell wall in the plant cells.
-The stomatal pores are largest when water is freely available which causes swelling of guard cells and results in its turgidity.
-The stomatal pores are closed when the availability of water is highly low and results in the flaccidity of guard cells.