Stoma

Not to be confused with Stroma.
For natural and surgically created body openings, see Stoma (medicine).
Stoma in a tomato leaf shown via colorized scanning electron microscope image
A stoma in horizontal cross section
The underside of a leaf. In this species (Tradescantia zebrina) the guard cells of the stomata are green because they contain chlorophyll while the epidermal cells are chlorophyll-free and contain red pigments.

In botany, a stoma (pl.: stomata, from Greek στόμα, "mouth"), also called a stomate (pl.: stomates), is a pore found in the epidermis of leaves, stems, and other organs, that controls the rate of gas exchange between the internal air spaces of the leaf and the atmosphere. The pore is bordered by a pair of specialized parenchyma cells known as guard cells that regulate the size of the stomatal opening.

The term is usually used collectively to refer to the entire stomatal complex, consisting of the paired guard cells and the pore itself, which is referred to as the stomatal aperture.[1] Air, containing oxygen, which is used in respiration, and carbon dioxide, which is used in photosynthesis, passes through stomata by gaseous diffusion. Water vapour diffuses through the stomata into the atmosphere as part of a process called transpiration.

Stomata are present in the sporophyte generation of the vast majority of land plants, with the exception of liverworts, as well as some mosses and hornworts. In vascular plants the number, size and distribution of stomata varies widely. Dicotyledons usually have more stomata on the lower surface of the leaves than the upper surface. Monocotyledons such as onion, oat and maize may have about the same number of stomata on both leaf surfaces.[2]: 5  In plants with floating leaves, stomata may be found only on the upper epidermis and submerged leaves may lack stomata entirely. Most tree species have stomata only on the lower leaf surface.[3] Leaves with stomata on both the upper and lower leaf surfaces are called amphistomatous leaves; leaves with stomata only on the lower surface are hypostomatous, and leaves with stomata only on the upper surface are epistomatous or hyperstomatous.[3] Size varies across species, with end-to-end lengths ranging from 10 to 80 μm and width ranging from a few to 50 μm.[4]

  1. ^ Esau, K. (1977). Anatomy of Seed Plants. Wiley and Sons. p. 88. ISBN 978-0-471-24520-9.
  2. ^ Weyers, J. D. B.; Meidner, H. (1990). Methods in stomatal research. Longman Group UK Ltd. ISBN 978-0582034839.
  3. ^ a b Willmer, Colin; Fricker, Mark (1996). Stomata. Springer. p. 16. doi:10.1007/978-94-011-0579-8. ISBN 978-94-010-4256-7. S2CID 224833888.
  4. ^ Fricker, M.; Willmer, C. (2012). Stomata. Springer Netherlands. p. 18. ISBN 978-94-011-0579-8. Retrieved 15 June 2016.