Assertion (A): The genetic code is universal. Reason (R): The same codon codes for the same amino acid in all organisms. MCQ with Answer and Explanation

Explanation:
Tuberculosis is a bacterial disease caused by Mycobacterium tuberculosis, primarily affecting the lungs. Polio is a viral disease caused by the poliovirus, attacking the nervous system. Tetanus is caused by the bacterium Clostridium tetani, which produces a neurotoxin that causes severe muscle spasms and affects the nervous system. Thus, only statement 3 is correct.

Explanation:
Prolactin, secreted by the anterior pituitary, is the primary hormone responsible for milk synthesis (lactation) after childbirth. Oxytocin causes milk ejection (let-down reflex). Estrogen and progesterone stimulate mammary duct and alveolar development during pregnancy but inhibit milk secretion; after delivery, their levels drop, allowing prolactin to act.

Explanation:
The pulmonary artery (trunk) exits the right ventricle and carries deoxygenated blood to the lungs for oxygenation. The pulmonary veins return oxygenated blood from the lungs to the left atrium. The aorta distributes oxygenated blood to the body, and the vena cava returns deoxygenated blood to the heart.