Stomata

Stomata are minute structures on plants found on the outer leaf skin layer, also known as the epidermis. They consist of two specialized cells, called guard cells that surround a tiny pore called a stoma. The word stomata means mouth in Greek because they allow communication between the internal and external environments of the plant. Their main function is to allow gases such as carbon dioxide, water vapor and oxygen to move rapidly into and out of the leaf. Stomata are found on all above-ground parts of plants including the petals of flowers, petioles, soft herbaceous stems and leaves. They are formed during the initial stages of the development of these various plant organs and therefore reflect the environmental conditions under which they grew.

Leaves are the main "food manufacturing" organs of plants. They make food from carbon dioxide and water in the presence of light during a process called photosynthesis. As stomata open in the presence of light, carbon dioxide will diffuse into the leaf as it is converted to sugars through photosynthesis inside the leaf. At the same time, water vapor will exit the leaf along a diffusive gradient through the stomata to the surrounding atmosphere through the process of transpiration. Consequently, plants face the dilemma of taking up carbon dioxide while losing water vapor through their stomata. If this water loss remains unchecked, they can deplete their water reserve. This depletion can become catastrophic to the physiological functioning of the plant given that is the most essential solvent in which biochemical and growth processes occur. Based on Darwinian principles, it is presumed that selective adaptation has driven plants to acquire characteristics which enable them to grow more quickly without diminishing the probability of survival. If plants have not acquired the characteristics to withstand changes in water availability in their growth environment, plants may exacerbate their water shortage by not regulating the size of their stomata apertures in an optimal manner and may fail to survive when water availability declines.

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