Question

What causes opening of stomata
A. Thin wall of guard cell facing stomatal pore is stretched more, curves in and the pore opens.
B. Thin wall of guard cell facing stomatal pore is stretched more, moves in and the pore opens.
C. As the thin wall of the guard cell is stretched less, the guard cell facing the stomatal pore moves in and the pore opens.
D. Thick wall of the guard cell facing the stomatal pore is stretched less, moves in and the pore opens.

Answer 1

Hint: A stoma or stomata are a tiny pore-like structure. It is noticed in the epidermis tissue of leaves and stems. These stomata help in controlling the rate of gas exchange. The pore is enclosed by a pair of parenchyma cells, which is called guard cells.

Complete answer:
The tiny pore found on the surface of the leaves is known as stomata. The stomata control the rate of gaseous exchange during the transpiration. Actually, these small pores are present in epidermis cells which can be opened or closed. The opening and closing of stomata are regulated by multiple mechanisms to control the function of transpiration. Stomata become close at high temperatures then it doesn't open again for the cooling of the leaf.
Stomata are consisting of two guard cells. i.e. stomata are surrounded by guard cells. They are mainly responsible for opening and closing the stomata to control the rate of transpiration. These cells look like bean-shaped or dumbbell-shaped. Later these cells are modified two form subsidiary cells. The inner side of the guard cell walls are thick and elastic and the outer cell wall is comparatively thin. Several microfibrils are found inside the guard cells which help in opening and closing of guard cells. Change in the turgidity or water level of these cells causes the opening and closing of stomata.
Light, the water content of cells, temperature, and mineral elements are the major factors that affect the opening and closing of stomata.
During transpiration, the transport of potassium ions in and out of the guard cells cause the opening and closing of stomata. In day time in the presence of light, potassium ions step inside the guard cells. This is why the water potential in the guard cells goes low and water steps inside the guard cells. This causes the guard cells swollen and they become turgid which leads to the opening of stomata pores. At night in the absence of light, potassium ions step out of guard cells, and water potential increases in the guard cells. So, the water of guard cells steps out and the cell becomes shrunk which leads the cell to close the stomata pores.
So we can say that the thick wall of the guard cell which is facing towards the stomatal pore is stretched less, and it moves in. Due to this stomatal pore is opened.

Hence the right answer to the question is option D.

Note: Stomata are a small pore-like structure that presents in the leaves which are responsible for the exchange of gases. These pores are surrounded by a pair of cells called guard cells. These cells regularize the opening and closing of the stomata. When the light falls on the leaf, potassium ion moves in and the water level increases in the guard cell and the stomata get open. But in absence of lights, potassium ions move out and the water level decreases, and the pore of stomata gets closed.