The opening and closing of the stomatal pore depends upon A) Oxygen B) Wind velocity C) Water in guard cells D) $CO_2$ concentration
Hint:Transpiration is a process that involves the loss of water from the plants to the surroundings in the form of water vapour. The transpiration process in plants takes place in the leaves.
Complete answer: To answer this question, we have to know about the structure of stomata that helps in the transpiration process. The stomata are the pores found in the epidermal surface of the leaves. It consists of two kidneys-like structures called guard cells. The inner wall of the guard cell is thicker in comparison to the outer wall. There are microfibrils found in the guard cells that involve in the opening and closing of the stomatal aperture. The opening and closing of the stomata is a result of change in the turgidity in the guard cells. In the daytime the guard cells involved in the photosynthesis process as a result the osmotic pressure increases and the guard cells absorb the water contained from the neighboring cells that make the guard cells turgid. Then the outer wall of the guard cell is pushed out and the inner wall pulls in the inward direction that causes the opening of the stomata. And during night due to unavailability or scarcity of water the stomata remain close as the guard cell becomes flaccid. Therefore, we can say that the opening and closing of the stomatal pore depends upon the water in guard cells.
Hence, the correct answer is ‘C’. Water in guard cells.
Note:The oxygen and the carbon dioxide exchange in the plants are carried out by osmosis process it does not relate with the opening and closing of the guard cells. The wind velocity does not relate to the transpiration process.