What is the role of guard cells in plants?

Guard cells in plants control the opening and closing of stomata to regulate gas exchange and water loss.

Guard cells are specialised cells in the epidermis of leaves, stems and other organs that are used to control gas exchange. They are produced in pairs with a gap between them that forms a pore, known as a stoma. The primary role of guard cells is to control the opening and closing of stomata, which are tiny openings in the surface of plants that allow for gas exchange. This process is crucial for photosynthesis, as it allows carbon dioxide to enter the plant and oxygen to be released.

Guard cells are sensitive to light and change shape in response to it. In the presence of light, they absorb water and swell, causing the stomata to open. This allows carbon dioxide to enter the plant for photosynthesis. At the same time, some water vapour escapes from the plant in a process known as transpiration. When it is dark, the guard cells lose water and become less turgid, causing the stomata to close. This helps to prevent excessive water loss from the plant when photosynthesis is not taking place.

In addition to light, guard cells also respond to other environmental factors such as humidity, temperature and carbon dioxide concentration. For example, if the external environment is very dry, the guard cells will close the stomata to prevent water loss. Similarly, if the carbon dioxide concentration inside the plant is high, the stomata will close to prevent further entry of carbon dioxide. This shows that guard cells play a crucial role in maintaining the balance of gases and water in plants, thereby helping them to survive and grow in different environmental conditions.