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transpiration
transpiration in botany, the loss of water by evaporation in terrestrial plants. Some evaporation occurs directly through the exposed walls of surface cells, but the greatest amount takes place through the stomates, or intercellular spaces (see leaf ). Transpiration functions to effect the ascent of sap from the roots to the leaves (thus supplying the food-manufacturing cells with water needed for photosynthesis) and to provide the moisture necessary for the diffusion of carbon dioxide into and oxygen out of these cells. The rate of transpiration is almost always far greater than the above functions would seem to warrant; in most plants 200 to 1,000 lb (90–450 kg) of water are transpired for each pound of solid material added to the plant. Various factors influence the transpiration rate. Photosynthesis, induced by light, has the effect of increasing the water pressure in the guard cells that border each stomate and that, in expanding, pull apart to widen the stomate aperture and thereby increase water loss. Low humidity promotes the diffusion of water vapor from the air passages inside the leaf into the outside air. A lack of water in the soil cuts down the water supply to the cells, thus limiting expansion of the guard cells. Therefore the rate is highest on a bright, dry day and lowest at night or in drought conditions. Morphological factors such as reduced leaf surfaces, a heavy cuticle layer on the leaves, low numbers of stomates, and stomates recessed below the other epidermal cells also lower the rate; desert plants such as conifers and cacti conserve water in these ways. Plants also lose some water by guttation, a process whereby water is exuded directly through pores called hydathodes. The reaction of a plant to excessive water loss is wilting and, eventually, death. |
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"transpiration." The Columbia Encyclopedia, 6th ed.. 2011. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. "transpiration." The Columbia Encyclopedia, 6th ed.. 2011. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1E1-transpir.html "transpiration." The Columbia Encyclopedia, 6th ed.. 2011. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1E1-transpir.html |
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transpiration
transpiration The loss of water vapour by plants to the atmosphere. It occurs mainly from the leaves through pores (stomata) whose primary function is gas exchange. The water is replaced by a continuous column of water (and dissolved nutrients) moving upwards from the roots within the xylem vessels. The flow of this column of water is known as the transpiration stream, which is maintained by root pressure and a combination of cohesive and adhesive forces in the xylem vessels according to the cohesion–tension theory (see cohesion). See also potometer.
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"transpiration." A Dictionary of Biology. 2004. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. "transpiration." A Dictionary of Biology. 2004. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O6-transpiration.html "transpiration." A Dictionary of Biology. 2004. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O6-transpiration.html |
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transpiration
transpiration The loss of water vapour from a plant to the outside atmosphere. It takes place mainly through the stomata of leaves and the lenticels of stems. Its function is disputed. It may reduce leaf temperature, but its absence from some tropical plants would suggest that this is not essential. It may also be important in mineral absorption and translocation. However, it may be merely an inevitable concomitant of gaseous exchange which, to be efficient, requires open stomata; as gases are exchanged, water is lost.
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MICHAEL ALLABY. "transpiration." A Dictionary of Ecology. 2004. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. MICHAEL ALLABY. "transpiration." A Dictionary of Ecology. 2004. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O14-transpiration.html MICHAEL ALLABY. "transpiration." A Dictionary of Ecology. 2004. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O14-transpiration.html |
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transpiration
transpiration The loss of water vapour from a plant to the outside atmosphere. It takes place mainly through the stomata of leaves and the lenticels of stems. Its function is disputed. It may reduce leaf temperature, but its absence from some tropical plants would suggest that this is not essential. It may also be important in mineral absorption and translocation. However, it may be merely an inevitable concomitant of gaseous exchange which, to be efficient, requires open stomata; as gases are exchanged, water is lost.
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Cite this article
MICHAEL ALLABY. "transpiration." A Dictionary of Plant Sciences. 1998. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. MICHAEL ALLABY. "transpiration." A Dictionary of Plant Sciences. 1998. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O7-transpiration.html MICHAEL ALLABY. "transpiration." A Dictionary of Plant Sciences. 1998. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O7-transpiration.html |
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transpiration
transpiration The removal of moisture from the soil by plant roots, its translocation up the stem to the leaves, and its evaporation through the stomata. The flow of water through the plant is known as the transpiration stream. It reduces leaf temperatures, and is thought to be important for mineral absorption and translocation within plants. The process imposes a number of environmental requirements upon plants; for example, wilting and desiccation result from an insufficient supply of water.
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AILSA ALLABY and MICHAEL ALLABY. "transpiration." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. AILSA ALLABY and MICHAEL ALLABY. "transpiration." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O13-transpiration.html AILSA ALLABY and MICHAEL ALLABY. "transpiration." A Dictionary of Earth Sciences. 1999. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O13-transpiration.html |
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transpiration
transpiration In plants, the loss of moisture as water vapour from leaf surfaces or other plant parts. Most of the water entering plant roots is lost by transpiration. The process is speeded up in light, warm, and dry conditions. The flow of water from the roots to the stomata is called the transpiration stream. See also photosynthesis; respiration; stoma
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"transpiration." World Encyclopedia. 2005. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. "transpiration." World Encyclopedia. 2005. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O142-transpiration.html "transpiration." World Encyclopedia. 2005. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O142-transpiration.html |
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