Stomata
Say it: STOH-muh-tuh
Stomata are tiny pores in the epidermis of leaves and stems, each opened and closed by two guard cells to control gas exchange and water loss.
Also: stoma, stomate, stomatal pore, leaf pore
Definition
What are stomata?
Stomata (singular stoma) are microscopic openings in the outer skin, or epidermis, of leaves and young stems. Each pore is flanked by a pair of curved guard cells that change shape to open or close it. In many plants stomata are most numerous on the lower surface of the leaf, where they connect to air spaces in the spongy mesophyll inside.
Stomata let carbon dioxide into the leaf for photosynthesis and let oxygen out, but every open pore also lets water vapor escape, which is transpiration. Plants therefore constantly trade carbon gain against water loss. Guard cells open the pore by pumping in potassium ions; water follows by osmosis, the cells swell with turgor pressure, and they bow apart. They close when the ions and water leave. Light, especially blue light, promotes opening, while darkness, high carbon dioxide inside the leaf and the drought hormone abscisic acid trigger closing.
Plants of dry or cold habitats often have sunken stomata that cut water loss, while water lilies and other plants with floating leaves carry theirs on the upper surface. Counting stomata on leaf peels is a common practical class exercise.
Word parts
Where does the word “stomata” come from?
- stoma
- mouthGreek stoma, plural stomata
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Terms that go with it
- TranspirationTranspiration is the escape of water vapor from a plant, mostly through open stomata in its leaves, which pulls more water up through the xylem.
- PhotosynthesisPhotosynthesis is the process in which plants, algae and cyanobacteria capture light energy and store it in sugar built from carbon dioxide and water.
- XylemXylem is the vascular tissue of plants that carries water and dissolved minerals upward from the roots to the stems and leaves.
- OsmosisOsmosis is the diffusion of water across a selectively permeable membrane, from the side with fewer dissolved solutes to the side with more.
- DiffusionDiffusion is the net movement of molecules from a region of higher concentration to one of lower concentration, driven by their random motion.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- OpenStax Biology 2e, 30.4 Leaves
- OpenStax Biology 2e, 30.5 Transport of Water and Solutes in Plants
- Yang et al. (2020), Light-Mediated Signaling and Metabolic Changes Coordinate Stomatal Opening and Closure, Frontiers in Plant Science
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