Roots will absorb water when external medium will be

Options

A. Hypotonic
B. Hypertonic
C. Isotonic
D. Concentrated

Answer

### Step-by-Step Solution:

1. **Understanding Water Absorption in Roots**:
- Water absorption in roots occurs primarily through a process called osmosis. Osmosis is the movement of water from an area of lower solute concentration to an area of higher solute concentration through a semi-permeable membrane.

2. **Analyzing the Options**:
- We have four options to consider regarding the external medium's concentration relative to the root cells:
- **Hypotonic**: This means the external medium has a lower concentration of solutes compared to the inside of the root cells.
- **Hypertonic**: This indicates that the external medium has a higher concentration of solutes than the inside of the root cells.
- **Isotonic**: This means that the concentration of solutes is equal inside and outside of the root cells.
- **Concentrated (Viscous)**: This refers to a medium that has a high concentration of solutes.

3. **Evaluating Each Option**:
- **Hypotonic**: In a hypotonic solution, water will move into the root cells because the concentration of solutes is lower outside the roots than inside. This is favorable for water absorption.
- **Hypertonic**: In a hypertonic solution, water would move out of the root cells into the external medium, leading to dehydration of the root cells.
- **Isotonic**: In an isotonic solution, there would be no net movement of water into or out of the root cells, which does not facilitate absorption.
- **Concentrated**: A concentrated solution would also lead to water moving out of the root cells, making absorption difficult.

4. **Conclusion**:
- The correct answer is **hypotonic**. Roots will absorb water when the external medium is hypotonic, as this allows water to move from an area of lower solute concentration (external medium) to an area of higher solute concentration (inside the root cells).

### Final Answer:
Roots will absorb water when the external medium is **hypotonic**.

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