Which is not parasitic protozoan

Options

A. Plasmodium vivax
B. Trypanosoma gambiense
C. Amoeba proteus
D. Entamoeba histolytica.

Answer

### Step-by-Step Solution:

1. **Understanding Protozoans**: Protozoans are unicellular eukaryotic organisms that can be classified based on their mode of nutrition. They can be parasitic or non-parasitic.

2. **Identifying Parasitic Protozoans**: Parasitic protozoans derive their nutrition from a host organism, often causing harm to the host. Examples include:
- **Plasmodium**: Causes malaria.
- **Trypanosoma**: Causes sleeping sickness.
- **Entamoeba histolytica**: Causes amoebiasis.

3. **Identifying Non-Parasitic Protozoans**: Non-parasitic protozoans do not rely on a host for nutrition. They often feed through processes like phagocytosis.

4. **Examining the Options**:
- **Plasmodium**: Parasitic (causes malaria).
- **Vivax**: A species of Plasmodium, also parasitic.
- **Trypanosoma**: Parasitic (causes sleeping sickness).
- **Gambiense**: A species of Trypanosoma, also parasitic.
- **Amoeba proteus**: Non-parasitic (feeds through phagocytosis).
- **Entamoeba histolytica**: Parasitic (causes amoebiasis).

5. **Conclusion**: Among the given options, **Amoeba proteus** is the only organism that is not a parasitic protozoan. It feeds by engulfing food particles rather than deriving nutrition from a host.

### Final Answer:
The correct option is **Amoeba proteus**.

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