The correct answer is: A. Exchange of gases.
Stomata are small pores on the surface of leaves that allow for the exchange of gases between the plant and the atmosphere. They are also responsible for the loss of water vapor from the plant, a process known as transpiration.
Option B: Exchange of lipids is incorrect because stomata do not play a role in the exchange of lipids. Lipids are a type of fat that is found in the cell membrane and other parts of the cell. They are not involved in the exchange of gases.
Option C: Exchange of water is incorrect because stomata are responsible for the loss of water vapor from the plant, not the uptake of water. Water is absorbed by the plant through the roots and transported to the leaves through the xylem.
Option D: Exchange of proteins is incorrect because stomata do not play a role in the exchange of proteins. Proteins are molecules that are essential for the function of the cell. They are not involved in the exchange of gases.
In conclusion, stomata help in the exchange of gases between the plant and the atmosphere. They are also responsible for the loss of water vapor from the plant, a process known as transpiration.