The force with which water molecules are held together in xylem is

Options

A. Imbibition pressure
B. Osmotic pressure
C. Adhesion force
D. Cohesion force

Answer

To answer the question about the force with which water molecules are held together in xylem, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Options**:
- We have four options: imbibation pressure, osmotic pressure, adhesion force, and cohesion force. We need to analyze each one to determine which describes the force holding water molecules together in xylem.

2. **Defining Imbibation Pressure**:
- Imbibation pressure is the pressure generated during the process of imbibation, which is the absorption of water by a substance. This does not specifically refer to the force between water molecules.

3. **Defining Osmotic Pressure**:
- Osmotic pressure is the pressure required to stop the flow of water through a semipermeable membrane during osmosis. This is related to the movement of water across membranes, not the force between water molecules in the xylem.

4. **Defining Adhesion Force**:
- Adhesion force refers to the attraction between different types of molecules. In the context of xylem, this would describe the interaction between water molecules and the walls of the xylem vessels, but not the force holding water molecules together.

5. **Defining Cohesion Force**:
- Cohesion force is the attractive force between molecules of the same substance. In the case of water, this force is responsible for holding water molecules together due to hydrogen bonding. This is the key force that allows water to move through the xylem in plants.

6. **Conclusion**:
- Based on the definitions and explanations, the force with which water molecules are held together in xylem is the **cohesion force**.

### Final Answer:
The force with which water molecules are held together in xylem is **cohesion force**.

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