Guard Cells - GCSE Biology Definition

Guard cells are specialised cells found on the surface of plant leaves, usually in pairs, surrounding tiny openings called stomata. These cells control the opening and closing of the stomata to regulate gases entering and leaving the leaf, such as carbon dioxide, oxygen, and water vapour. When guard cells take in water, they swell and cause the stomata to open, allowing the plant to take in carbon dioxide for photosynthesis. When they lose water, they shrink, causing the stomata to close, which helps to conserve water within the plant. This process is essential for maintaining a balance between photosynthesis, respiration, and water loss in plants.