Question

The bean shaped cells of the stomata are known as
(A) Guard cell
(B) Stoma
(C) Epidermis
(D) None of the above

Answer 1

Hint:Stomata, otherwise known as stomatal aperture are minute openings present in the plant tissue that aids in exchange of oxygen and carbon dioxide. Transpiration (evaporative loss of water) also takes place through stomata. The stomatal apparatus consists of stomatal aperture, guard cells, and subsidiary cells, which function as a single unit.

Complete answer:
Water present inside the plant tissue is lost by evaporation through stomata (minute openings) present along with the epidermal cells of the leaves. This is called transpiration. Stomata also helps in exchange of gases like oxygen and carbon dioxide, which are involved in cellular respiration.

The stomatal apparatus constitutes a stomatal aperture or pore, guard cells and subsidiary cells. The stomata is open during the daytime and closed during the night. The stomatal aperture or pore is enclosed by bean shaped cells called guard cells. And the guard cells are surrounded by cylindrical shaped subsidiary cells. The opening and closing of the stomata is due to changes in the turgidity of the guard cell. Guard cells possess micro fibrils which help in bulging and shrinking of itself. It also possesses chloroplasts which helps in performing photosynthesis. The shape of the guard cell depends on the plant type. In dicot plants, guard cells are bean shaped, whereas, in monocot plants, they are dumbbell shaped.
Understanding the options one by one,
(A) Guard cell : This is the correct answer. Cells enclosing the stomatal aperture are bean shaped and are known as guard cells.
(B) Stoma : Stoma is the singular form of stomata. They are minute openings present on the leaves. This is not the correct answer.
(C) Epidermis : Epidermis is the outermost layer of plant tissue, which is irregularly shaped. This is not the correct answer.

Therefore ,the correct answer is option (A) is correct.

Note:Guard cells are modified epidermal cells which are present on the leaves. Depending on the type of plant, the shape of the guard cell varies. Monocot plants have dumbbell shaped guard cells and dicot plants have bean shaped guard cells. The important function of a guard cell is to aid in opening and closing of the stomatal pore or aperture..