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 determine which statements about acquired immunity are correct, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement I: Acquired immunity is a non-specific type of immunity.**
- Acquired immunity, also known as adaptive immunity, is specific to particular pathogens. It develops over time and is not present at birth. In contrast, non-specific immunity is referred to as innate immunity, which responds to all pathogens in the same way. Therefore, this statement is **false**.

2. **Statement II: The primary and secondary immune responses are carried out with the help of lymphocytes present in our blood.**
- The primary and secondary immune responses involve B lymphocytes and T lymphocytes, which are indeed present in the blood. B lymphocytes are responsible for antibody production, while T lymphocytes play a role in cell-mediated immunity. Thus, this statement is **true**.

3. **Statement III: Each antibody molecule has two small heavy chains and two longer light chains respectively.**
- The structure of an antibody is represented as H2L2, indicating that there are two heavy chains (which are longer) and two light chains (which are shorter). The statement incorrectly describes the lengths of the chains. Therefore, this statement is **false**.

4. **Statement IV: Cell-mediated immunity is mediated by T-lymphocytes.**
- Cell-mediated immunity is indeed mediated by T-lymphocytes, which mature in the thymus gland. This type of immunity is a crucial part of the acquired immune response. Hence, this statement is **true**.

### Conclusion:
Based on the analysis:
- **Correct Statements**: II and IV
- **Incorrect Statements**: I and III

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

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