Biology · Gaseous Exchange

The opening and closing of stomata are controlled by the turgidity of guard cells. When solutes accumulate in guard cells, water enters by osmosis, making them turgid and opening the stomata. Conversely, when solutes leave the guard cells, water exits, causing the cells to become flaccid and the stomata to close. This process ensures gas exchange and water regulation in plants. Options A and D refer to concepts not directly applicable to stomatal regulation, while Option C describes a condition resulting from the loss of turgidity, not a controlling factor.

Option A is incorrect because turbidity relates to cloudiness in a liquid and is unrelated to the physiological processes in guard cells.

Option B is correct. Turgidity refers to the state of being swollen with water, which is crucial in the opening and closing of stomata. When guard cells are turgid, they swell and open the stomatal pore; when they lose water and become less turgid, the pore closes.

Option C is incorrect. Flaccidity refers to the condition of being limp due to loss of water. While it describes a state opposite to turgidity, it alone does not directly control stomatal movement.

Option D is incorrect. While turgor pressure is indeed involved in the process, the term 'turgor force' is not commonly used to describe the mechanism of stomatal movement.