Water absorption of root hairs occurs until

Options

A. Concentration of water in the cell sap is higher
B. Salt concentration in cell sap is higher
C. They are separted from the soil by a selectively permeable membrane
D. Water potential is lower

Answer

**Step-by-Step Solution:**

1. **Understanding Water Absorption in Root Hairs:**
Water absorption in root hairs primarily occurs through the process of osmosis, where water moves from an area of higher concentration to an area of lower concentration.

2. **Analyzing the Options:**
- **Option 1: Concentration of water in the cell sap is higher.** This suggests that if the concentration of water in the cell sap of root hairs becomes higher than that in the soil, water absorption will stop.
- **Option 2: Salt concentration in cell sap is higher.** If the salt concentration is higher in the cell sap, it would create a lower water potential in the root hairs, causing water to move out, which is not the case for absorption.
- **Option 3: They are separated from soil by a selectively permeable membrane.** While this is true, it does not directly relate to the stopping of water absorption.
- **Option 4: Water potential is lower.** This is incorrect because for water absorption to occur, the water potential in the soil must be higher than that in the root hairs.

3. **Conclusion:**
Water absorption in root hairs will continue until the concentration of water in the cell sap becomes equal to or higher than that in the surrounding soil. Therefore, the correct answer is **Option 1: Concentration of water in the cell sap is higher.**

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