Read the following statements about acquired immunity. Which of the following statements are correct ?
I. Acquired immunity is a non - specific type of immunity .
II. The primary and secondary immune responses are carried out with the help of lymphocytes present in our blood.
III. Each antibody molecules has two smll heavy chains and two longer light chains respectively.
IV. Cell - mediated immunity is mediated by T - lymphocytes.

Options

A. I and III
B. I, II and IV
C. II, III and IV
D. II and IV

Answer

To solve the question regarding acquired immunity, we need to evaluate each statement provided and determine its correctness.

### Step-by-Step Solution:

1. **Evaluate Statement I**:
- **Statement**: Acquired immunity is a non-specific type of immunity.
- **Analysis**: This statement is incorrect. Acquired immunity is actually a specific type of immunity that targets specific pathogens. It develops after exposure to a specific antigen.
- **Conclusion**: **Incorrect**

2. **Evaluate Statement II**:
- **Statement**: The primary and secondary immune responses are carried out with the help of lymphocytes present in our blood.
- **Analysis**: This statement is correct. Both primary and secondary immune responses involve lymphocytes (B cells and T cells) that are crucial for the adaptive immune response.
- **Conclusion**: **Correct**

3. **Evaluate Statement III**:
- **Statement**: Each antibody molecule has two small heavy chains and two longer light chains respectively.
- **Analysis**: This statement is incorrect. Each antibody molecule actually consists of two heavy chains (which are longer) and two light chains (which are shorter).
- **Conclusion**: **Incorrect**

4. **Evaluate Statement IV**:
- **Statement**: Cell-mediated immunity is mediated by T-lymphocytes.
- **Analysis**: This statement is correct. T-lymphocytes (T cells) play a crucial role in cell-mediated immunity, which involves the direct killing of infected cells and the activation of other immune cells.
- **Conclusion**: **Correct**

### Summary of Findings:
- Statement I: Incorrect
- Statement II: Correct
- Statement III: Incorrect
- Statement IV: Correct

### Final Answer:
The correct statements about acquired immunity are **II and IV**.