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  4. Assertion (A) In old persons, there is gradually weakening of immune system. Reason (R) It is because of degeneration of thymus gland.

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Q. Assertion (A) In old persons, there is gradually weakening of immune system.
Reason (R) It is because of degeneration of thymus gland.

Chemical Coordination and Integration

Solution:

Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
In old persons, there is gradually weakening of immune system because of degeneration of thymus gland. Thymus secretes a hormone named thymosin which stimulates the development of certain kinds of WBCs involved in generating immunity. It is prominent at the time of birth, but it gradually atrophies in adults and its disappearance causes ageing.