Which cell organelle is not bound by any membrane?

Options

A. Mitochondria
B. Chloroplast
C. ER
D. Ribosome

Answer

To answer the question "Which cell organelle is not bound by any membrane?", we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Options**: We start by listing the organelles mentioned in the question:
- Mitochondria
- Chloroplast
- Endoplasmic Reticulum
- Ribosome

2. **Analyze Mitochondria**:
- Mitochondria are known as the powerhouse of the cell and are involved in energy production.
- They are **double membrane-bound organelles**, consisting of an outer membrane and an inner membrane.
- **Conclusion**: Mitochondria are not the answer.

3. **Analyze Chloroplast**:
- Chloroplasts are involved in photosynthesis.
- They are also **double membrane-bound organelles** with an outer and inner membrane.
- **Conclusion**: Chloroplasts are not the answer.

4. **Analyze Endoplasmic Reticulum (ER)**:
- The endoplasmic reticulum comes in two forms: rough ER and smooth ER.
- It is a **single membrane-bound organelle**.
- **Conclusion**: Endoplasmic reticulum is not the answer.

5. **Analyze Ribosome**:
- Ribosomes are the sites of protein synthesis in the cell.
- They are **not bound by any membrane** at all.
- **Conclusion**: Ribosomes are the answer.

6. **Final Answer**: The cell organelle that is not bound by any membrane is **Ribosome**.