Which is not a free living protozoan

Options

A. Euglena
B. Amoeba
C. Giardia
D. Noctiluca.

Answer

To determine which organism is not a free-living protozoan, we can analyze the provided options: Euglena, Amoeba, Giardia, and Noctiluca.

### Step-by-Step Solution:

1. **Understanding Free-Living Protozoans**:
- Free-living protozoans are organisms that can live independently in their environment, such as in water or soil, without relying on a host organism for survival.

2. **Analyzing the Options**:
- **Euglena**: This is a genus of single-celled organisms that can photosynthesize and live freely in freshwater environments. Therefore, Euglena is a free-living protozoan.
- **Amoeba**: This is another type of free-living protozoan that can be found in various environments, including freshwater and soil. It feeds on bacteria and other small organisms. Thus, Amoeba is also a free-living protozoan.
- **Giardia**: This organism is known to be a parasite. It primarily resides in the intestines of its host, which is often humans. Giardia is transmitted through contaminated food and water, making it dependent on a host for survival. Therefore, Giardia is not a free-living protozoan.
- **Noctiluca**: This is a genus of bioluminescent marine protozoans that live freely in ocean waters. Hence, Noctiluca is also a free-living protozoan.

3. **Conclusion**:
- Based on the analysis, the organism that is not a free-living protozoan is **Giardia**. It is a parasitic organism that requires a host to survive.

### Final Answer:
The organism that is not a free-living protozoan is **Giardia**.

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