Stomata and Guard Cells in Gas Exchange
Stomata are small pores primarily found on the underside of leaves that play a role in regulating gas exchange in plants. Each stoma is flanked by two specialised guard cells that control its opening and closing, effectively acting as gatekeepers.
The shape and turgidity of guard cells are influenced by water availability. When the plant has enough water, guard cells take up water, become turgid and curve outward, causing the stomata to open. This opening allows carbon dioxide to diffuse into the leaf, which is required for photosynthesis, while oxygen, a byproduct of this process, diffuses out. However, water vapour can also escape through the open stomata in a process called transpiration.
When the plant experiences water stress or high temperatures, guard cells lose turgor pressure, becoming flaccid, which leads to the closing of the stomata. This closure reduces water loss through transpiration but also limits the intake of carbon dioxide and the release of oxygen, temporarily slowing down photosynthesis.
The ability of guard cells to regulate the opening and closing of stomata allows the plant to balance its need for gas exchange with the need to conserving water, particularly in arid or drought-prone environments.