The main function of the contractile vacuole is :

Options

A. synthesis of carbohydrate
B. eliminating excess water
C. to be a photoreceptor to detect light
D. resistance for survival during winter and times of drought

Explanation

**Step-by-Step Solution:**

1. **Understanding the Role of Contractile Vacuoles**:
- Contractile vacuoles are specialized organelles found in certain cells, particularly in unicellular organisms like protozoa and some plant cells. Their primary function is to manage water balance within the cell.

2. **Identifying the Functions**:
- The main functions of contractile vacuoles include:
- **Regulating Water Content**: They help in expelling excess water that enters the cell through osmosis.
- **Preventing Cell Lysis**: By expelling excess water, contractile vacuoles prevent the cell from swelling and eventually bursting (lysis).

3. **Elimination of Excess Water**:
- The correct answer to the question is that the main function of the contractile vacuole is the elimination of excess water. This is crucial for maintaining osmotic balance and ensuring the cell's survival.

4. **Mechanism of Action**:
- Contractile vacuoles work by contracting to expel the stored water. When the vacuole contracts, it forces the excess water out of the cell, thus preventing any potential damage from too much water.

5. **Conclusion**:
- Therefore, the main function of the contractile vacuole is to eliminate excess water, which protects the cell from lysis and maintains homeostasis.