A conserved structure is

Options

A. Contractile vacuole
B. Flagellum
C. Pseudopodium
D. All the above.

Answer

To determine which of the given options is a conserved structure, we need to analyze each option based on the definition of a conserved structure. A conserved structure is one that remains similar or identical in appearance and function throughout evolution.

### Step-by-Step Solution:

1. **Understanding Conserved Structures**:
- A conserved structure is one that has remained relatively unchanged throughout evolution. This means it should be similar or identical in different organisms.

2. **Analyzing the Options**:
- **Contractile Vacuole**:
- These are round structures found in cells that function in osmoregulation. However, they can vary in size among different cells. Since they differ in size, they cannot be classified as conserved structures.
- **Flagellum**:
- Flagella are thread-like projections that extend from the cell and are primarily used for movement. They are found in various organisms, including bacteria and eukaryotes, and their structure is generally consistent across these organisms. Therefore, flagella can be considered a conserved structure.
- **Pseudopodium**:
- Pseudopodia are temporary projections of the cell membrane that help in movement and feeding, especially in amoeba. They are not always present and vary in form and function, making them not conserved structures.

3. **Conclusion**:
- Based on the analysis, the only option that fits the definition of a conserved structure is **flagellum**. Therefore, the correct answer is option 2, flagellum.

### Final Answer:
The conserved structure is **flagellum**.

---