Root pressure is maximum when

Options

A. absorption is high but transpiration is low
B. absorption is high but transpiration is high
C. both absorption and transpiration is high
D. both absorption and transpiration is low.

Answer

### Step-by-Step Solution:

1. **Understanding Root Pressure**:
- Root pressure is a phenomenon that occurs in plants where a positive pressure builds up in the xylem sap, primarily due to the active absorption of water by the roots. This pressure can help in the upward movement of water within the plant.

2. **Factors Affecting Root Pressure**:
- Root pressure is influenced by two main factors: the rate of water absorption by the roots and the rate of transpiration (water loss through leaves).
- When water absorption is high, it contributes to an increase in root pressure. Conversely, when transpiration is high, it can lead to a decrease in root pressure due to the loss of water.

3. **Analyzing the Options**:
- **Option 1**: Absorption is high but transpiration is low.
- **Option 2**: Absorption is high and transpiration is high.
- **Option 3**: Both absorption and transpiration are high.
- **Option 4**: Both absorption and transpiration are low.
- Among these options, we need to determine which scenario would lead to maximum root pressure.

4. **Identifying the Correct Option**:
- The first option states that absorption is high while transpiration is low. This scenario is ideal for maximizing root pressure because the roots are taking in a lot of water, and since transpiration is low, less water is being lost. This creates a strong positive pressure in the xylem.
- The other options either have high transpiration, which would counteract the root pressure, or low absorption, which would not generate enough pressure.

5. **Conclusion**:
- Therefore, the correct answer is that root pressure is maximum when absorption is high but transpiration is low.