What role do the adhesive property of water and evaporation play in generating tension forces in leaf cell walls?

Sourav PanNovember 9, 2024

Answered

The adhesive property of water and evaporation play significant roles in generating tension forces in leaf cell walls, which are crucial for the transport of water in plants. Here’s how these processes work together:

Adhesive Property of Water

1. Adhesion to Cell Walls:
   • Water molecules exhibit adhesive properties, meaning they are attracted to other substances, such as the hydrophilic surfaces of plant cell walls (particularly those made of cellulose). This adhesion allows water to cling to the cell walls of mesophyll cells in the leaves.
2. Formation of Menisci:
   • As water evaporates from the surfaces of mesophyll cells into the air spaces within the leaf, it creates a meniscus (curved surface) at the interface between the water and the air. The adhesive forces between water molecules and the cell walls help maintain this meniscus, which is critical for creating tension.

Evaporation and Tension Generation

1. Water Loss through Transpiration:
   • When water evaporates from the leaf surface (transpiration), it decreases the amount of water available at the surface of the mesophyll cells. This loss generates a negative pressure (tension) within the leaf, as water molecules are drawn out from the liquid film covering the cell walls.
2. Increased Tension Forces:
   • The evaporation process increases the curvature of the water surface in the menisci, which enhances tension forces in the leaf cell walls. This tension pulls more water into the cells from nearby xylem vessels, creating a continuous flow of water upward from roots to leaves.
3. Transpiration Pull:
   • The negative pressure created by transpiration acts as a “pull” on the column of water in the xylem vessels. As water evaporates from stomata, it generates a transpiration pull that draws water upward through capillary action and cohesion among water molecules.