Regulacja transpiracji przez aparaty szparkowe

Plants require ample carbon dioxide from the atmosphere to conduct photosynthesis. The surfaces of plant leaves contain openings that facilitate gas exchange. These openings are called stomata.

Sunlight triggers the opening of stomata, allowing carbon dioxide to enter the leaf when it is needed for photosynthesis. Oxygen is a byproduct of photosynthesis and escapes into the atmosphere through the stomata.

A pair of guard cells regulates each stomatal opening. These specialized cells swell when they take in water from neighboring cells via osmosis, creating an opening that enables gas exchange. When water leaves the guard cells, they shrink and the stoma closes. 

The concentration of ions influences the amount of water in the guard cells. Sunlight stimulates guard cells to take up potassium ions. The increase in the potassium concentration drives water into the cells, thereby opening the stoma. 

When potassium leaves the guard cells, water follows via osmosis. The now flaccid guard cells close the stoma.

While open stomata facilitate gas exchange, they also allow water to escape from leaves through evaporation. The evaporative water loss—or transpiration—allows the long-distance movement of water through the plant.

Transpiration is typically greatest on warm and sunny days. However, if a plant cannot acquire sufficient water, its stomata will rapidly close to prevent wilting.

Interestingly, even if kept in the dark, plants will open and close stomata on a regular, 24-hour cycle, due to an internal clock.

The opening and closing of stomata are tightly regulated, allowing plants to respond to specific environmental conditions. In their function as gate-keepers, stomata efficiently balance gas exchange and transpiration.