Which is not example of secondry lymphoid organ

Options

A. Appendix
B. Thymus gland
C. Tonsils
D. Peyer's patches of small intestine.

Answer

To determine which of the given options is not an example of a secondary lymphoid organ, we need to understand the difference between primary and secondary lymphoid organs.

### Step-by-Step Solution:

1. **Define Lymphoid Organs**:
- Lymphoid organs are involved in the immune response and the development of immune cells. They are classified into two categories: primary and secondary lymphoid organs.

2. **Identify Primary Lymphoid Organs**:
- Primary lymphoid organs are where the maturation and development of immune cells occur. The main examples of primary lymphoid organs are:
- Bone marrow
- Thymus gland

3. **Identify Secondary Lymphoid Organs**:
- Secondary lymphoid organs are where mature immune cells encounter antigens. Examples include:
- Spleen
- Tonsils
- Mucosa-associated lymphoid tissue (MALT)
- Peyer's patches in the small intestine
- Appendix

4. **Analyze the Options**:
- **Appendix**: Considered a secondary lymphoid organ.
- **Thymus gland**: This is a primary lymphoid organ where T-cells mature.
- **Tonsils**: These are secondary lymphoid organs.
- **Peyer's patches**: These are also secondary lymphoid organs.

5. **Conclusion**:
- The only option that is not a secondary lymphoid organ is the **Thymus gland** (Option B).

### Final Answer:
The correct answer is **Thymus gland**.

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