Question

Give an experiment to demonstrate cohesion - tension theory.

Answer 1

The cohesion-tension theory describes the intermolecular attraction that explains the process of water flow upwards through the xylem of plants given by Dixon and Jolly. To demonstrate the cohesion-tension theory, we have to show that the water present in xylem should experience a strong pulling force. A simple experiment supports this prediction. If we find a leaf that is actively transpiring and cut its petiole, the watery fluid in the xylem, the xylem sap, withdraws from the edge toward the inside of the leaf petiole (Figure). According to the cohesion-tension theory, this observation is due to a transpirational pull at the air-water interface in leaf cells. This shows the xylem sap is under tension which evidenced the cohesion-tension theory.