Which is a unit of immune system

Options

A. lymphocytes
B. erythocytes
C. chondrocyte
D. parasite

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for a unit of the immune system. We need to identify which of the provided options is directly involved in immune functions.

2. **Analyzing the Options**:
- **Option 1: Lymphocyte**: Lymphocytes are a type of white blood cell (WBC) that play a crucial role in the immune response. They are classified into B-cells and T-cells.
- **Option 2: Erythrocyte**: Erythrocytes, or red blood cells (RBCs), are primarily responsible for transporting oxygen in the blood. They do not play a direct role in the immune system.
- **Option 3: Chondrocyte**: Chondrocytes are cells found in cartilage and are not involved in the immune response.
- **Option 4: Parasite**: Parasites are organisms that live on or in a host organism and can cause disease, but they are not units of the immune system.

3. **Identifying the Correct Answer**: Based on the analysis, lymphocytes are the only option that is a unit of the immune system. They are essential for both humoral and cell-mediated immunity.

4. **Conclusion**: The correct answer is **Lymphocyte**.