Question

Give biological reason for the following:

Tensile strength of water.

Answer 1

Cohesion

1. As the water is lost from mesophyll cells due to transpiration, it increases the suction pressure for the ascent of sap.
2. So, they start withdrawing water from the xylem channels.
3. The water column in the xylem vessel comes under tension or negative pressure of around 10-20 atm.
4. However, the water column does not break due to the forces of adhesion and cohesion.
5. Cohesion is a type of force where water molecules are bound to each other by hydrogen bonds.
6. This cohesion of water molecules develops a cohesive force or tensile strength of around 200 atm.

Hence, the tensile strength of water develops due to cohesion.