Root pressure is maximum when :

Options

A. Transpiration is high and absorbtion is low
B. Transpiration is very low and absorption is high
C. Transpiration is absent
D. Guttation is absent

Answer

To determine when root pressure is maximum, we need to analyze the conditions that affect root pressure in plants. Here’s a step-by-step solution:

### Step 1: Understand Root Pressure
Root pressure is a positive pressure that develops in the roots of plants when they absorb water and minerals from the soil. This pressure helps in the upward movement of water and nutrients through the xylem to the stems and leaves.

### Step 2: Identify Factors Affecting Root Pressure
Root pressure is influenced by two main factors:
- **Transpiration Rate**: This is the process of water vapor loss from plant leaves. High transpiration rates can lead to a decrease in root pressure.
- **Absorption Rate**: This refers to how much water and minerals the roots take up from the soil. High absorption rates contribute positively to root pressure.

### Step 3: Analyze the Options
Now, let’s evaluate the given options based on our understanding:
- **A. Transpiration is high and absorption is low**: This would not support high root pressure because high transpiration can reduce root pressure.
- **B. Transpiration is very low and absorption is high**: This condition supports maximum root pressure since low transpiration means less loss of water, allowing for greater pressure buildup from absorption.
- **C. Transpiration is absent**: While this might seem favorable, transpiration cannot be completely absent in plants, making this option impractical.
- **D. Guttation is absent**: Guttation is the process of water exudation from the leaves, which is a result of root pressure. If guttation is absent, it indicates that root pressure is not functioning effectively.

### Step 4: Conclusion
Based on the analysis, the condition for maximum root pressure occurs when transpiration is very low and absorption is high. Therefore, the correct answer is **B**.

### Final Answer:
**Root pressure is maximum when transpiration is very low and absorption is high (Option B).**

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