What is correct about root pressure ?

Options

A. Provides a modest push in the over all process of water transport
B. Play a major role in water movement in tall trees
C. Is not observable at night
D. Cannot explain the loss of impure water from hydathodes

Answer

### Step-by-Step Solution:

1. **Definition of Root Pressure**: Root pressure is the pressure exerted in the roots of plants that helps in the upward movement of water through the xylem. It is generated when water is absorbed from the soil into the roots.

2. **Mechanism of Root Pressure**: When roots absorb water, it creates a positive pressure that pushes water upward through the plant. This is particularly important in maintaining the flow of water to the leaves where transpiration occurs.

3. **Role of Transpiration**: Transpiration is the process by which water vapor is lost from the plant, primarily through small openings in the leaves called stomata. This loss of water creates a negative pressure (transpirational pull) that helps in pulling water up from the roots.

4. **Interaction with Transpirational Pull**: While root pressure provides a moderate push to help move water up, it is the transpirational pull that is the primary driving force for water movement in tall plants and trees.

5. **Conditions Affecting Root Pressure**: Root pressure is generally observed during the day when transpiration is occurring. However, it may not be as effective at night when transpiration rates drop significantly.

6. **Limitations of Root Pressure**: Root pressure cannot account for the loss of water from the leaves, especially during conditions where transpiration is high. It also does not explain the movement of water in very tall trees, where the transpirational pull is much more significant.

### Conclusion:
The correct statement about root pressure is that it provides a moderate push for water transport in plants, but it is not the sole mechanism and is influenced by transpiration.