Which of the following is not membrane-bound

Options

A. Ribosomes
B. Lysosomes
C. Mesosomes
D. Vacuoles

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks which of the given options is not membrane-bound. This means we need to identify the structure that does not have a surrounding membrane.

2. **Analyzing the Options**:
- **Ribosomes**: These are small structures that are involved in protein synthesis. They are not surrounded by a membrane, making them non-membrane-bound organelles.
- **Lysosomes**: These are membrane-bound organelles that contain hydrolytic enzymes for digestion. They have a lipid bilayer membrane.
- **Mesosomes**: These are infoldings of the plasma membrane in prokaryotic cells and are also considered membrane-bound.
- **Vacuoles**: These are storage organelles in cells that are surrounded by a membrane called the tonoplast.

3. **Identifying the Correct Answer**: Based on the analysis, ribosomes are the only option that is not membrane-bound. Therefore, the correct answer is **Ribosomes**.

4. **Conclusion**: The answer to the question "Which of the following is not membrane-bound?" is **Ribosomes**.