The greatest contribution of root pressure is

Options

A. to re- establish the continuous chains of water molecules in the xylem which often break under the enormous tensions created by transpiration.
B. to play a major role in water movement up tall tress over 50 feet in height.
C. to act as a main driving force to push water from the roots in the xylem towards the leaves .
D. to give water high tensile strength and high capillarity action.

Answer

To solve the question regarding the greatest contribution of root pressure, we need to analyze each option provided and understand the role of root pressure in the movement of water in plants.

### Step-by-Step Solution:

1. **Understanding Root Pressure**:
- Root pressure is generated in the roots of plants when water is absorbed from the soil. It creates a positive pressure that can push water upwards in the xylem.

2. **Analyzing the Options**:
- **Option 1**: To re-establish the continuous chains of water molecules in the xylem which often break under the enormous tension created by transpiration.
- This option suggests that root pressure helps maintain the continuity of the water column in the xylem, which is indeed a significant role of root pressure.

- **Option 2**: To play a major role in water movement up tall trees over 50 feet in height.
- This option is incorrect because root pressure alone cannot push water to such great heights. The main mechanism for water transport in tall trees is transpirational pull.

- **Option 3**: To act as a main driving force to push water from the roots in the xylem towards the leaves.
- This option is also incorrect. While root pressure does contribute to water movement, the primary driving force for water transport to the leaves is transpirational pull, not root pressure.

- **Option 4**: To give water high tensile strength and high capillarity action.
- This option is misleading. The tensile strength and capillarity are properties of the xylem vessels themselves, not directly a result of root pressure.

3. **Conclusion**:
- After analyzing all the options, the greatest contribution of root pressure is indeed **Option 1**: to re-establish the continuous chains of water molecules in the xylem which often break under the enormous tension created by transpiration.

### Final Answer:
The correct answer is **Option 1**.

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