What is the role of guard cells in transpiration?

Guard cells regulate transpiration by controlling the opening and closing of stomata on plant surfaces.

Guard cells are specialised cells in the epidermis of leaves, stems and other plant organs. They play a crucial role in transpiration, which is the process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems and flowers. The primary function of guard cells is to control the opening and closing of stomata, the tiny openings on plant surfaces that allow for gas exchange.

Stomata are surrounded by two kidney-shaped guard cells. When these cells absorb water, they become turgid or swollen, causing the stomata to open. This allows for the exchange of gases, including the release of water vapour from the plant to the atmosphere, a process known as transpiration. Conversely, when guard cells lose water, they become flaccid or limp, causing the stomata to close and thus reducing transpiration.

The opening and closing of stomata by guard cells is a complex process influenced by various factors. These include light intensity, carbon dioxide concentration, and temperature. For instance, in the presence of light, photosynthesis occurs, leading to the production of glucose in the guard cells. This increases their osmotic potential, causing them to absorb water and become turgid, thereby opening the stomata.

In addition to regulating transpiration, guard cells also play a vital role in photosynthesis. By controlling the opening and closing of stomata, they regulate the entry of carbon dioxide, which is essential for photosynthesis, into the plant. Therefore, the role of guard cells in transpiration is not only crucial for water regulation in plants but also for their overall growth and survival.