Explain how hydrogen bonding of water molecules is involved with movement of water in the xylem by cohesion-tension in transpiration pull and by adhesion to cellulose in cell walls
Explain how hydrogen bonding of water molecules is involved with movement of water in the xylem by cohesion-tension in transpiration pull and by adhesion to cellulose in cell walls
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The movement of water in the xylem of plants is primarily driven by two key processes: cohesion and adhesion, both of which are influenced by hydrogen bonding among water molecules. Here’s how these processes work together during transpiration:
Cohesion-Tension and Transpiration Pull
- Cohesion: Water molecules are polar, which allows them to form hydrogen bonds with each other. This creates a cohesive force that causes water molecules to stick together. As water evaporates from the stomata of leaves during transpiration, it creates a tension (or negative pressure) in the leaf.
- Transpiration Pull: The continuous evaporation of water from the leaf surfaces creates a negative pressure that pulls more water upward from the roots through the xylem vessels. Because of cohesion, the water molecules remain attached to one another, forming a continuous column of water that extends from the roots, through the stem, and up to the leaves. This cohesive column is crucial for maintaining the movement of water against the force of gravity.
Adhesion to Cellulose in Cell Walls
- Adhesion: In addition to cohesion, water molecules also exhibit adhesion, which is the attraction between water molecules and other substances. In the case of the xylem, water adheres to the cellulose fibers in the plant cell walls.
- Facilitating Movement: This adhesion helps to counteract the force of gravity by allowing water to stick to the walls of the xylem vessels, creating a narrow pathway that promotes the upward movement of water. The adhesive forces between water and the cellulose help maintain the integrity of the water column and prevent it from breaking.
Combined Effect
The combination of cohesion (water molecules sticking together) and adhesion (water molecules sticking to xylem walls) enables the efficient transport of water from the roots to the leaves. As water is pulled up through the xylem due to transpiration, the cohesive and adhesive properties of water ensure that it continues to flow uninterrupted, supporting the plant’s physiological processes and maintaining its overall health.
BNO Team
