Question

Assertion (A): Lymphocytes arise from the bone marrow and present in the blood and lymph serve as natural killer cells.
Reason (R): Lymphocytes migrate to thymus, where they develop into T-cells and begin to mature.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true, but (R) is not the correct explanation of (A).
• C. (A) is true, but (R) is false.
• D. (A) is false, but (R) is true.

Hint:

Lymphocytes include B-cells, T-cells, and NK cells; only T-cells mature in the thymus, while NK cells develop elsewhere.

Answer 1

The Correct Option is B

Step 1: Lymphocytes, including natural killer (NK) cells, do arise from bone marrow and are present in blood and lymph — Assertion is true.
Step 2: Some lymphocytes migrate to the thymus to develop into mature T-cells — Reason is true.
Step 3: However, the Reason explains T-cell development, not the role of lymphocytes as NK cells — so option (B) is correct.