Introduction:
The cohesion-tension theory explains the movement of water in plants. This theory proposes that the movement of water from the roots to the leaves is driven by the combined forces of cohesion, adhesion, and tension.

Key Points:
The cohesion-tension theory can be explained in the following steps:

1. Transpiration:
- Transpiration is the process by which water evaporates from the leaves of the plant.
- It occurs through small openings on the surface of leaves called stomata.
- Transpiration creates a suction force that pulls water up from the roots.

2. Cohesion:
- Cohesion refers to the attraction between water molecules.
- Water molecules are cohesive due to their polarity, allowing them to form hydrogen bonds with each other.
- This cohesion creates a continuous column of water in the xylem vessels from roots to leaves.

3. Adhesion:
- Adhesion refers to the attraction between water molecules and the walls of the xylem vessels.
- The walls of the xylem vessels are made up of cellulose and lignin, which are polar and attract water molecules.
- Adhesion helps in maintaining the integrity of the water column and prevents it from breaking.

4. Tension:
- Tension is created when water molecules are pulled up from the roots due to transpiration.
- As water evaporates from the leaves, it creates a negative pressure or tension in the xylem vessels.
- This tension pulls water molecules upward through the xylem, from the roots to the leaves.

5. Capillary Action:
- Capillary action is the movement of water within narrow spaces against gravity.
- It occurs due to the combined forces of cohesion and adhesion.
- Water can move up the xylem vessels against gravity, driven by capillary action.

6. Root Pressure:
- Root pressure is another factor that aids in the movement of water in plants.
- It is the pressure exerted by the roots to push water up the xylem vessels.
- Root pressure is primarily responsible for the movement of water in herbaceous plants.

Conclusion:
The cohesion-tension theory explains how water moves from the roots to the leaves in plants. The combined forces of cohesion, adhesion, and tension allow water molecules to form a continuous column in the xylem vessels. Transpiration, cohesion, adhesion, tension, capillary action, and root pressure all contribute to the movement of water, ensuring that plants receive the necessary water and nutrients for their survival and growth.