Stomata

Stomata are microscopic pores found mostly on the surfaces of leaves and young stems that allow plants to exchange gases with their environment. They are critical for photosynthesis, respiration, and transpiration.​

Structure of Stomata

Stomatal Pore: The central opening through which gases and water vapor move in and out of the plant.​

Guard Cells: Two specialized, kidney- or dumbbell-shaped cells flank each stoma and control its opening and closing. They contain chloroplasts and change shape based on water content, regulating pore size.​

Subsidiary Cells: Sometimes found adjacent to guard cells, these cells support guard cell movements in certain stomata types.​

Epidermal Cells: Surround the stomata complex, providing protection and mechanical support.​

Function

Gas Exchange: Stomata enable the absorption of carbon dioxide (CO2) for photosynthesis and the release of oxygen (O2) produced in the process.​

Transpiration: Water vapor exits through stomata, helping to regulate plant temperature and draw nutrients and water upward from roots (transpiration pull).​

Regulation: Guard cells open stomata when turgid (full of water), typically during the day, and close them when flaccid (water loss), helping to conserve water—especially under dry or hot conditions.​

Opening and Closing Mechanism

Stomata open when guard cells take in water (become turgid) due to osmotic changes, often triggered by light or internal signals.​

When water is scarce, guard cells lose turgor, the stomatal pore closes to prevent water loss.​