Amoeba moves when

Options

A. Upper part of plasma-gel changes to plasmasol
B. Lower part of plasmasol changes into gel
C. Upper part of plasmasol changes into plasmagel
D. All the above.

Answer

### Step-by-Step Solution

1. **Understanding Amoeba Movement**: Amoeba moves using a process that involves the transformation of its cytoplasm between two states: the fluid state (plasma sol) and the solid state (plasma gel). This process is essential for its locomotion.

2. **Sol-Gel Theory**: The movement of amoeba is explained by the Sol-Gel theory, which was proposed by Goldarg and Lorsch. According to this theory, the cytoplasm of amoeba can change from a fluid state to a solid state and vice versa.

3. **Cytoplasmic States**:
- **Plasma Sol**: This is the fluid state of the cytoplasm, which allows for movement and flow.
- **Plasma Gel**: This is the solid state of the cytoplasm, which provides structure and support.

4. **Mechanism of Movement**:
- At the **anterior end** of the amoeba, the plasma sol converts into plasma gel, allowing the cell to extend forward.
- At the **posterior end**, the plasma gel converts back into plasma sol, allowing the cell to retract and move forward.

5. **Analyzing the Options**:
- **Option 1**: "Upper part of plasma gel changes to plasma sol" - This is incorrect as it does not describe the movement accurately.
- **Option 2**: "Lower part of plasma sol changes into gel" - This is also incorrect as it misrepresents the process.
- **Option 3**: "Upper part of plasma sol changes into plasma gel" - This is correct as it describes the forward movement of amoeba.
- **Option 4**: "All of the above" - This is incorrect since not all options are true.

6. **Conclusion**: The correct answer is **Option 3**, which states that the upper part of plasma sol changes into plasma gel, facilitating the movement of the amoeba.