Root pressure -

Options

A. is not sufficient to rise water above ground level
B. is negative in all except the tallest trees .
C. is the driving force for the mass flow of sugar
D. can push water upto small heights in the stem

Answer

### Step-by-Step Solution for the Question on Root Pressure

1. **Understanding Root Pressure**:
- Root pressure is defined as a positive hydrostatic pressure that develops in the roots of plants due to the accumulation of water. This pressure is generated when water enters the roots through osmosis.

2. **Evaluating the Options**:
- **Option 1**: "Not sufficient to rise water above ground level."
- Root pressure can indeed push water a small height above ground level, especially in herbaceous plants. Therefore, this statement is incorrect.

- **Option 2**: "Negative in all except the tallest trees."
- Root pressure is not negative; it is a positive pressure that occurs in smaller plants, not in tall trees due to high transpiration rates. This statement is also incorrect.

- **Option 3**: "The driving force for the mass flow of sugar."
- Root pressure is related to water movement in the xylem and does not drive the mass flow of sugars, which occurs in the phloem. Hence, this statement is incorrect.

- **Option 4**: "Can push water up to small heights in the stem."
- This statement is correct. Root pressure can indeed push water a few meters up into the stem, particularly in smaller plants.

3. **Conclusion**:
- After evaluating all options, the only correct statement regarding root pressure is **Option 4**: "Can push water up to small heights in the stem."

### Final Answer:
**The correct option regarding root pressure is Option 4: "Can push water up to small heights in the stem."**