Assertion : Some diseases that attack in childhood do not attack again.
Reason : Memory cells play an important role.

Options

A. If both assertion and reason are true and reason is the correct explanation of assertion.
B. If both assertion and reason are true but reason is not the correct explanation of assertion.
C. If assertion is true but reason is false.
D. If both assertion and reason are false.

Answer

A

Explanation

After the infection disappears as a result of antigen-antibody interaction, some of the specific lymphocytes remain in circulation as "memory cells" that give rise to more effector cells and memory cells in case of a second attack of antigens. The effector cells have a life of a few days only, and the memory cells live long, some even for whole life. That is why the second attack of the infectious disease elicits quick response.