Question

Basis of stomata opening is
a. Exosmosis
b. Endosmosis
c. Decrease in cell sap concentration
d. Plasmolysis of guard cells

Answer 1

Hint: In the green plants, exchange of the gases such as carbon dioxide and oxygen take place. the exchange of gases takes place through specialized pores present in the epidermis and are known as stomata. The stomata helps in regulating water loss within the plant and gases exchange.

Complete answer:
Stomata is a pore that is found in the epidermis of leaves, stems, and other organs of the plant. It controls the rate of gas exchange by allowing the exchange of gases and evaporation of water. The pore is formed by a pair of specialized cells known as guard cells. The guard cells are kidney shaped cells and are two in number. They are responsible for regulation of the size of the stomatal opening.

The turgor pressure of the two guard cells mediates the opening and closure of the stomatal pore. It is controlled by movements of large quantities of ions and sugars which move into and out of the guard cells. Turgor pressure can be described as the force within the cell that pushes the plasma membrane against the cell wall and is caused by the osmotic flow of water. It is regulated within cells by osmosis and causes the cell wall to expand during growth.

In case of lower turgor pressure, the cell has a low water concentration and closing the stomata would help to preserve water while in high turgor pressure keeps the stomata open for gas exchanges necessary for photosynthesis

When water enters into the guard cells through the process of endosmosis, the guard cells swell and become turgid. This allows the opening of the stomatal pore through the movement of the inner wall of guard cells outside.

In exosmosis, the movement of water takes place towards outside of the cell as a result, the guard cells become flaccid. As the guard cells turn flaccid, the stomatal pore closes.

The process in which cells lose water to the outside in a hypertonic solution is known as plasmolysis. As a result of plasmolysis, turgor pressure decreases and cells shrink away. It is also known as shrinking of cell membrane and results in closing of the stomata.

Hence, the correct answer is option (B).

Note: The minute pore present on the underside of the leaves that are used for transpiration and gaseous exchange are known as stomatal pore. These pores are made up of two guard cells. The guard cell helps in the opening and closing of the stomatal pore. In the process of endosmosis, water enters the guard cells and they swell up and thereby increase the turgor pressure of the cells. This allows the opening of the stomatal pore and thus, endosmosis is the basis of opening of the pore of the stomata.