Which of the following acts as a filter of the blood by trapping blood borne micro-organisms and also has a large reservoir of erythrocytes ?

Options

A. Bone marrow
B. Thymus
C. Spleen
D. Tonsils

Answer

To solve the question, "Which of the following acts as a filter of the blood by trapping blood borne micro-organisms and also has a large reservoir of erythrocytes?", we will analyze the options provided and determine which one fits the description.

### Step-by-Step Solution:

1. **Understanding the Question**:
- We need to identify an organ that filters blood by trapping microorganisms and also serves as a reservoir for erythrocytes (red blood cells).

2. **Analyzing the Options**:
- **Option 1: Bone Marrow**
- Bone marrow is primarily responsible for the production of blood cells (including erythrocytes) but does not filter blood or trap microorganisms. Therefore, this option is incorrect.

- **Option 2: Thymus**
- The thymus is involved in the maturation of T-cells, which are crucial for the immune response. It does not function as a blood filter or reservoir for erythrocytes. Thus, this option is also incorrect.

- **Option 3: Spleen**
- The spleen plays a significant role in filtering blood. It traps blood-borne microorganisms and old or damaged erythrocytes. Additionally, it serves as a reservoir for erythrocytes, making this option correct.

- **Option 4: Tonsils**
- Tonsils are lymphoid tissues that help in immune response but are not involved in filtering blood or serving as a reservoir for erythrocytes. Therefore, this option is incorrect.

3. **Conclusion**:
- The correct answer is **Option 3: Spleen**, as it acts as a filter for blood and has a large reservoir of erythrocytes.

### Final Answer:
**Option 3: Spleen**