Stoma
/ˈstoʊmə/
Definition
Stoma refers to a microscopic pore in the epidermis, the outer cell layer of leaves and young stems. Each stoma is usually bordered by two guard cells that open or close the pore. This regulates gas exchange, allowing carbon dioxide in for photosynthesis while controlling the release of oxygen and water vapor through transpiration. Most stomata occur on leaves, often in greater numbers on the undersides.
Function in Plants
- Gas exchange control: A stoma regulates the movement of carbon dioxide into the leaf and oxygen and water vapor out. This balance directly affects photosynthesis and helps the plant manage water loss.
- Response to conditions: Opening and closing can change with light, humidity, temperature, and soil moisture. During drought or heat stress, a stoma may close to conserve water, though this can also slow sugar production.
- Placement on leaves: Many land plants have more on the underside of leaves than on the upper surface. That pattern can reduce direct exposure to sun and dry air, which helps limit evaporation.
- Clue to plant adaptation: The number and arrangement can reflect habitat and strategy. Desert plants, aquatic plants, and shade plants often show different patterns, so these features are useful in plant physiology and comparative botany.
Related Terms
Guard cell
Guard cell refers to one of the two specialized plant epidermal cells that surround a stoma, the tiny pore on a leaf or…
Pore
Pore refers to a small opening in a plant surface or cell wall. In plants, the term often describes stomatal pores on…
Transpiration
Transpiration is the plant process of losing water vapor to the air, mainly through tiny leaf pores called stomata, and…
Photosynthesis
Photosynthesis is the biological process in which plants, algae, and some bacteria use light energy to convert carbon…
Osmosis
Osmosis is a biological process in which water moves across a selectively permeable membrane, such as a plant cell…
Plasmolysis
Plasmolysis is a biological process in plant cells in which the cell membrane pulls away from the cell wall after the…
Humidity
Humidity is the amount of water vapor in the air around a plant, usually discussed as relative humidity, the percentage…