Question

What is ascent of sap? Explain cohesion-tension theory for it.

Answer 1

Ascent of Sap is the movement of water from a region of positive pressure such as the root to a region of negative pressure such as the shoot regions caused by multiple forces like Transpiration pull and root pressure.

Cohesion tension theory says that the movement of water in the upwards direction against gravity is guided by the attractive forces between the particles of water which is known as cohesion and thus gives rise to surface tension which pulls the water upwards from the root through the xylem and this is aided by Transpiration pull and capillary action of water. This is the main mechanism of transport of water in plants. Transpiration pull causes a suction effect on the water column and water rises up, aided by its capillary action. Cohesion (with other water molecules) and adhesion (with the walls of xylem vessels) helps in a continuous flow of water without breaking the column. the