Osmotic expansion of a cell kept in water is chiefly regulated by

Options

A. Ribosomes
B. Mitochondria
C. Vacuoles
D. Plastids

Answer

**Step-by-Step Solution:**

1. **Understanding Osmosis**: Osmosis is the movement of water molecules from an area of lower solute concentration (more dilute) to an area of higher solute concentration (less dilute) through a semipermeable membrane. In simpler terms, water moves toward where there is less water (more solute).

2. **Setting the Scenario**: When a cell is placed in water, it is in a hypotonic solution, meaning the concentration of solutes outside the cell is lower than inside the cell. This causes water to move into the cell.

3. **Identifying the Process**: The influx of water into the cell leads to osmotic expansion. This process is often referred to as deplasmolysis, where the cell swells as water enters.

4. **Role of Cell Organelles**: The question asks which part of the cell regulates this osmotic expansion. While various organelles have different functions, we need to identify the one that specifically helps in managing water balance.

5. **Examining Organelles**:
- **Ribosomes**: These are involved in protein synthesis and do not regulate water movement.
- **Mitochondria**: Known as the powerhouse of the cell, they generate ATP but do not play a direct role in water regulation.
- **Vacuoles**: These are storage organelles that can hold water and help maintain turgor pressure within the cell. They play a crucial role in regulating water balance and osmotic pressure.
- **Plastids**: These are involved in photosynthesis and storage of food but do not directly regulate water movement.

6. **Conclusion**: The organelle chiefly responsible for regulating osmotic expansion of a cell kept in water is the **vacuole**. It helps in maintaining the internal environment of the cell by managing the influx of water.

**Final Answer**: The osmotic expansion of a cell kept in water is chiefly regulated by the **vacuole**.

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