Which protozoan is unlikely to have contractile vacuole ?

Options

A. Euglena
B. Paramecium
C. Amoeba
D. Plasmodium

Answer

To determine which protozoan is unlikely to have a contractile vacuole, we need to understand the function of a contractile vacuole and the habitats of the protozoans listed.

### Step-by-Step Solution:

1. **Understand the Function of Contractile Vacuole**:
- A contractile vacuole is an organelle that helps regulate the water content within a cell. It is particularly important for organisms that live in aquatic environments, as it helps prevent the cell from bursting due to excess water intake.

2. **Identify the Protozoans**:
- The protozoans mentioned are Euglena, Paramecium, Amoeba, and Plasmodium.

3. **Analyze Each Protozoan**:
- **Euglena**: This organism is aquatic and has a contractile vacuole to manage water balance.
- **Paramecium**: Also an aquatic organism, Paramecium possesses a contractile vacuole for similar reasons.
- **Amoeba**: As a unicellular organism found in water, Amoeba has a contractile vacuole to regulate its internal environment.
- **Plasmodium**: This protozoan is a parasite that lives within the blood cells of its hosts (mosquitoes and humans) and does not inhabit a free aquatic environment.

4. **Conclusion**:
- Since Plasmodium is an endoparasite and does not live in water, it is unlikely to have a contractile vacuole. Therefore, the correct answer is **Plasmodium**.

### Final Answer:
Plasmodium is the protozoan that is unlikely to have a contractile vacuole.

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