Biology – Transport mechanisms | e-Consult

Stomata are small pores, primarily located on the lower epidermis of leaves, that play a vital role in transpiration. They are surrounded by guard cells, which regulate their opening and closing. Stomata facilitate the diffusion of water vapour from the leaf into the atmosphere.

When the guard cells take up water, they become turgid, causing the stomatal pore to open. This opening allows water vapour to diffuse out of the leaf. The rate of transpiration is therefore directly linked to the degree of stomatal opening.

The opening and closing of stomata are regulated by a variety of factors, including light intensity, carbon dioxide concentration, and water availability. For example, in bright light, stomata tend to open to allow for efficient carbon dioxide uptake for photosynthesis, even though this also increases water loss. Conversely, when water is scarce, the plant hormone abscisic acid (ABA) is released, triggering the closing of stomata to reduce water loss, even if it means a reduction in carbon dioxide uptake.