Assertion (A): Double circulation is seen in birds and mammals. Reason (R): It ensures complete separation of oxygenated and deoxygenated blood. MCQ with Answer and Explanation

Explanation:
Innate immunity is the non-specific, inborn defense mechanism present from birth. It includes physical barriers (skin, mucous membranes), physiological barriers (stomach acid, tears), cellular barriers (neutrophils, macrophages), and cytokine barriers (interferons). Antibodies and memory cells are part of acquired (adaptive) immunity.

Explanation:
Edward Jenner developed the first successful vaccine against smallpox in 1796 using cowpox virus. Pasteur developed rabies vaccine, Koch TB bacterium, Salk polio.

Explanation:
The lac repressor protein (product of lacI gene) binds to the operator sequence, preventing RNA polymerase from transcribing the structural genes. When lactose is present, allolactose (inducer) binds the repressor, causing it to release the operator, allowing transcription. This is negative regulation.