Image: Transpiration Overview

Description: 1-Water molecules enter the roots passively, passing through the cortex, and are guided to xylem tissue by the Casparian strip. A concentration gradient of solutes within the xylem leads to further passive transport of water into the vessel elements or traicheids. 2-Once the water has entered the xylem, the forces of adhesion and cohesion take effect. Adhesion causes the molecules to adhere to sides of the vessels, and cohesion causes the molecules to adhere to each other, forming a column of water that extends from the roots to the top of the plant. 3-Water from the xylem is let into the spongy mesophyll, where it can come into contact with stomata. When the stomata are open, the cells in this layer are exposed to the outside air, and evaporation occurs. When water molecules evaporate out of the stomata, they create tension in the water column, as the forces of cohesion pull nearby molecules up with them, creating pulling force down the length of the xylem.

Mader, Sylvia S. Biology, Tenth. New York: McGraw Hill, 2010. Print.
Author: Laurel Jules
Usage Terms: Creative Commons Attribution-Share Alike 3.0
License: CC-BY-SA-3.0
License Link: http://creativecommons.org/licenses/by-sa/3.0/
Attribution Required?: Yes