Opening and Closing of Stomata due to Osmosis

Stomata are tiny pores present on the surface of leaves and stems of plants that regulate the exchange of gases and water vapor between the plant and the atmosphere. The opening and closing of stomata are essential for photosynthesis, respiration, and transpiration in plants. It is due to the process of osmosis that the stomata open and close.

What is Osmosis?

Osmosis is the movement of water molecules from a region of higher concentration to a region of lower concentration through a semi-permeable membrane. In plants, the guard cells that surround the stomata act as a semi-permeable membrane.

Opening of Stomata

During the day, when there is light, the guard cells take up water by osmosis from the surrounding epidermal cells, which leads to an increase in their turgor pressure. The water enters the guard cells due to the higher concentration of solutes in the guard cells. This increase in turgor pressure causes the guard cells to swell and bend outwards, leading to the opening of stomata. The opening of stomata allows the exchange of gases and water vapor between the plant and the atmosphere, which is essential for photosynthesis.

Closing of Stomata

During the night, when there is no light, the guard cells lose water by osmosis to the surrounding epidermal cells, which leads to a decrease in their turgor pressure. The water leaves the guard cells due to the higher concentration of solutes in the epidermal cells. This decrease in turgor pressure causes the guard cells to become flaccid and return to their original shape, leading to the closing of stomata. The closing of stomata reduces the loss of water vapor from the plant, which is essential to prevent dehydration.

Conclusion

Thus, the opening and closing of stomata are due to the process of osmosis, which is regulated by the turgor pressure of the guard cells. The opening of stomata allows the exchange of gases and water vapor between the plant and the atmosphere, while the closing of stomata reduces the loss of water vapor from the plant.

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