Stomata are microscopic pores found mainly on the underside of plant leaves that facilitate gas exchange for photosynthesis. Stomatal opening is the process by which these pores widen and open.
Carbon dioxide is taken up by the leaf through the stomata and transported to chloroplasts filled with the pigment chlorophyll. Here, it is converted into glucose using sunlight and water. At the same time, oxygen is released through the stomata as a by-product of photosynthesis.
As water vapour also evaporates through the stomata, the plant can control when they open and close to prevent dehydration. The regulation of the openings is also governed by light intensity, carbon dioxide levels and the plant’s access to water. The two cells that surround the stomatal opening and control the inflow and outflow are called guard cells or lip cells, and look like tiny mouths.
The reason why the stomatal openings, also known as stomata, are usually found on the underside of leaves is that the shade reduces transpiration. This also protects the pores from becoming clogged with dirt and debris. However, in certain conifers, such as some species of spruce, they can be found on all surfaces.
Links
ReThink – Plant Knowledge
Britannica – Stomate 
Youtube – Stamata Function
Wikipedia – Guard Cells
May 2026, TÄNKOM | Revised August 2026, RETHINK
