Cohesion tension theory Flashcards
What is the Cohesion Tension Theory? Is it active or passive?
Currently accepted theory of how water moves up the plant from root to leaves. It’s a passive process, heat required to evaporate water from the leaves.
Outline the theory
1) Water is lost from the leaf due to transpiration
2) This lowers the water potential of the cell
3) Water is pulled up by the xylem, creating tension
4) Water molecules cohere/ stick because of hydrogen bonds
5) This causes the continuous flow of water up the xylem
6) Adhesion of water to the walls of the xylem
What is the evidence to the theory?
Tension has been measured in the xylem as plants transpire.
If a column breaks, air bubbles in the xylem form, preventing cohesion.
Respiratory inhibitors don’t inhibit this
Diameter of trees decrease when they’re transpiring
