Which one of the following organisms is not an eukaryote ?

Options

A. Paramecium caudatum
B. Escherichia coli
C. Euglena viridis
D. Amoeba proteus

Answer

To determine which organism is not a eukaryote among the given options, we will analyze each organism based on their classification.

### Step-by-Step Solution:

1. **Understand Eukaryotes**:
- Eukaryotes are organisms that have a true nucleus and membrane-bound organelles. They belong to various kingdoms, including Protista, Fungi, Plantae, and Animalia.

2. **Identify the Organisms**:
- The options provided are:
- A) Paramecium caudatum
- B) Escherichia coli
- C) Euglena viridis
- D) Amoeba proteus

3. **Analyze Each Option**:
- **A) Paramecium caudatum**:
- This organism is a protozoan that belongs to the kingdom Protista. Since it has a true nucleus, it is a eukaryote.
- **B) Escherichia coli**:
- This is a type of bacteria that belongs to the kingdom Monera. Bacteria are prokaryotes, meaning they do not have a true nucleus or membrane-bound organelles. Therefore, E. coli is not a eukaryote.
- **C) Euglena viridis**:
- This organism is a protistan algae, also belonging to the kingdom Protista. It has a true nucleus and is classified as a eukaryote.
- **D) Amoeba proteus**:
- This is another protozoan that belongs to the kingdom Protista. Like Paramecium and Euglena, it is also a eukaryote.

4. **Conclusion**:
- Among the options, the only organism that is not a eukaryote is **Escherichia coli** (Option B), as it is a prokaryote.

### Final Answer:
**B) Escherichia coli is not a eukaryote.**