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The Function of the Stoma
The Function of the Stoma. A stoma -- plural stomata -- allows a plant to control the amount of carbon dioxide and water vapor moving in and out of the plant. Stomata are found on all parts of the plant except the underground parts, particularly on the leaves.
A stoma -- plural stomata -- allows a plant to control the amount of carbon dioxide and water vapor moving in and out of the plant. Stomata are found on all parts of the plant except the underground parts, particularly on the leaves.
Description
A stoma, which is Greek for "mouth," is an opening in the plant's skin. Each stoma is bordered by two guard cells that control the size of the opening, based on factors like atmospheric conditions and light levels.
Considerations
Plants need open stomata during the day so carbon dioxide for photosynthesis can enter. The "cost" of open stomata is water loss through transpiration, and through natural selection, each plant species has found the optimum amount of opening to minimize the cost-to-benefit ratio in its environment.
Number
Deciduous trees have more stomata per square millimeter than grasses. Stomata density increases when the benefit of more stomata is highest or the cost is lowest; parts of the plant in bright light, plants in humid environments and plants in low-carbon dioxide conditions have the highest stomata densities.
