Question

Will the ascent of sap be possible without the cohesion and adhesion of the water molecules? Explain.

Answer 1

Cohesion

Cohesion is defined as the force of attraction between two like molecules. As a result of this property the water molecules in the xylem vessels remain together causing a continuous stream of water. This property assists transpiration pull as the whole water column is sucked up without any air in between.


Adhesion

Adhesion is defined as the force of attraction between two different molecules (water molecules and polar surfaces like the xylem vessels). Due to this property of water no space exists between the surface of the xylem vessels and water column helping in transpiration pull.


Ascent of sap

The upward movement of sap in xylem vessels is called ascent of sap. In the absence of cohesive and adhesive forces the water column will break and cease the upward movement of water.