AskDefine | Define transpiration

Dictionary Definition



1 the passage of gases through fine tubes because of differences in pressure or temperature
2 the process of givng off or exhaling water vapor through the skin or mucous membranes
3 the emission of water vapor from the leaves of plants

User Contributed Dictionary



  1. The loss of water by evaporation in terrestrial plants, especially through the stomata; accompanied by a corresponding uptake from the roots.
  2. The process of giving off water vapour through the skin or mucous membranes.
  3. The passage of gases through fine tubes.


botany: the loss of water by evaporation in terrestrial plants
  • French: transpiration
physiology: the process of giving off water vapour through the skin or mucous membranes
the passage of gases through fine tubes

Extensive Definition

Transpiration is the evaporation of water from the aerial parts of plants, especially leaves but also stems, flowers and roots. Leaf transpiration occurs through stomata, and can be thought of as a necessary "cost" associated with the opening of stomata to allow the diffusion of carbon dioxide gas from the air for photosynthesis. Transpiration also cools plants and enables mass flow of mineral nutrients and water from roots to shoots. Mass flow is caused by the decrease in hydrostatic (water) pressure in the upper parts of the plants due to the diffusion of water out of stomata into the atmosphere. Water is absorbed at the roots by osmosis, and any dissolved mineral nutrients travel with it through the xylem.
The rate of transpiration is directly related to the degree of stomatal opening, and to the evaporative demand of the atmosphere surrounding the leaf. The amount of water lost by a plant depends on its size, along with the surrounding light intensity, temperature, humidity, and wind speed (all of which influence evaporative demand). Soil water supply and soil temperature can influence stomatal opening, and thus transpiration rate.
A fully grown tree may lose several hundred gallons (a few cubic meters) of water through its leaves on a hot, dry day. About 90% of the water that enters a plant's roots is used for this process. The transpiration ratio is the ratio of the mass of water transpired to the mass of dry matter produced; the transpiration ratio of crops tends to fall between 200 and 1000 (i.e., crop plants transpire 200 to 1000 kg of water for every kg of dry matter produced) .
Transpiration rate of plants can be measured by a number of techniques, including potometers, lysimeters, porometers, and heat balance sap flow gauges.
Desert plants and conifers have specially adapted structures, such as thick cuticles, reduced leaf areas, sunken stomata and hairs to reduce transpiration and conserve water. Many cacti conduct photosynthesis in succulent stems, rather than leaves, so the surface area of the shoot is very low. Many desert plants have a special type of photosynthesis, termed Crassulacean acid metabolism or CAM photosynthesis in which the stomata are closed during the day and open at night when transpiration will be lower.

External links

transpiration in Bulgarian: Транспирация
transpiration in Catalan: Transpiració vegetal
transpiration in Czech: Transpirace
transpiration in Danish: Transpiration (botanik)
transpiration in German: Transpiration
transpiration in Estonian: Transpiratsioon
transpiration in Spanish: Transpiración
transpiration in Persian: تعرق
transpiration in French: Transpiration végétale
transpiration in Indonesian: Transpirasi
transpiration in Italian: Traspirazione
transpiration in Hebrew: דיות
transpiration in Lithuanian: Transpiracija
transpiration in Hungarian: Transpiráció
transpiration in Macedonian: Транспирација
transpiration in Dutch: Transpiratie (hydrologie)
transpiration in Japanese: 蒸散
transpiration in Polish: Transpiracja
transpiration in Portuguese: Transpiração
transpiration in Russian: Транспирация
transpiration in Simple English: Transpiration
transpiration in Slovak: Transpirácia
transpiration in Slovenian: Transpiracija
transpiration in Serbian: Транспирација
transpiration in Finnish: Transpiraatio
transpiration in Swedish: Transpiration
transpiration in Turkish: Transpirasyon
transpiration in Ukrainian: Транспірація
transpiration in Chinese: 蒸腾作用
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