Root hairs absorb water when

Options

A. transipration is low
B. soil solution is isotonic
C. salt concentration of cell sap is high
D. salt concentration of soil is high.

Answer

To solve the question "Root hairs absorb water when?", we will analyze the options provided and understand the conditions under which root hairs effectively absorb water.

### Step-by-Step Solution:

1. **Understanding Root Hairs**:
- Root hairs are extensions of root cells that increase the surface area for absorption. They play a crucial role in the uptake of water and nutrients from the soil.

2. **Analyzing the Options**:
- **Option A: Transpiration is low**: When transpiration is low, there is less water loss from the leaves, which can lead to higher water availability in the roots. This condition can promote water absorption.
- **Option B: Soil solution is isotonic**: If the soil solution is isotonic to the root cells, there is no net movement of water into the cells. This condition does not favor water absorption.
- **Option C: Soil concentration of cell sap is high**: If the concentration of cell sap in root hairs is higher than that in the soil, water will move into the root hairs by osmosis. This condition is favorable for water absorption.
- **Option D: Soil concentration of cell is high**: This option seems to be a repetition of option C and suggests that if the soil concentration is high, it would not favor water absorption since water would move out of the root hairs.

3. **Conclusion**:
- The most favorable condition for root hairs to absorb water is when the concentration of cell sap in the root hairs is higher than that in the soil, which corresponds to **Option C**.

### Final Answer:
Root hairs absorb water when the soil concentration of cell sap is high (Option C).