How do stomata regulate transpiration?

Stomata regulate transpiration by opening and closing to control the amount of water vapour that escapes from plant leaves.

Stomata are tiny openings or pores, primarily found on the underside of plant leaves. They play a crucial role in photosynthesis, allowing the exchange of gases, including the intake of carbon dioxide and the release of oxygen. However, they also facilitate transpiration, which is the process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems and flowers.

The regulation of transpiration by stomata is a delicate balancing act. When stomata are open, they allow carbon dioxide to enter the leaf for photosynthesis, but this also means that water vapour can escape. Conversely, when stomata are closed, the loss of water through transpiration is reduced, but so is the intake of carbon dioxide for photosynthesis. Therefore, stomata must open and close at appropriate times to optimise both photosynthesis and water conservation.

The opening and closing of stomata are controlled by guard cells, which surround each stoma. When the guard cells are filled with water, they swell, causing the stoma to open. Conversely, when the guard cells lose water, they shrink, causing the stoma to close. This process is influenced by various factors, including light, temperature, humidity, and the concentration of carbon dioxide.

In bright light, for example, the guard cells photosynthesise and produce glucose, which increases their osmotic potential and causes them to take in water and swell, opening the stomata. In contrast, in darkness, the guard cells respire and lose glucose, reducing their osmotic potential, causing them to lose water and shrink, closing the stomata. Similarly, high temperatures can increase the rate of evaporation of water from the leaf, causing the guard cells to lose water and close the stomata to prevent excessive water loss.

In summary, stomata regulate transpiration by opening and closing in response to environmental conditions, thereby controlling the amount of water vapour that escapes from the leaf. This process is crucial for maintaining the plant's water balance and ensuring efficient photosynthesis.