STOMATA

Stomata are microscopic pores found on the underside of leaves. You will find the stomata in the epidermal tissue. The stomata is bounded by two half moon shaped guard cells that function to vary the width of the pore. Each guard cell contains chloroplasts. The glucose concentration of the cells changes with the photosynthetic activity and therefore it is the guard cells that regulate the opening and closing of the stomata.

Why do plants have a STOMATA?

Plants carry on the process of photosynthesis by combining together several ingredients in their leaves. Some of these materials are gaseous (carbon dioxide), some are liquid (water), and one is energy (sunlight). If one were to look at the anatomy of a leaf, it would be easy to see how these materials are brought to the leaf so that they can form the food. The Stomata is the way in which this transfer of ingredients can occur, transferring the CO2, light and water from the surrounding atmosphere into the plant.

In light, the guard cells swell, causing the pore to be at its widest, and CO2 diffuses into the leaf and into the cells to be assimilated in photosynthesis. In the dark or under drought conditions the guard cells are not turgid, the stomata are closed and no photosynthesis takes place. Opening of the stomata not only allows CO2 to diffuse into the leaf, but allows water vapor to diffuse out of the leaf. The alteration in the size of the stomata occur in response to a variety of the external stimuli such as light, carbon dioxide concentration and water.

The stomata is situated on the underside of the leaf for the reason that if it were on the top side, the plant would lose too much water. Because the guard cells are partially light activated, plants under direct sunlight wouldconstantly have their stomata open and would thus lose much water, causing the plant to die.