The functional unit of the human lung is the: MCQ with Answer and Explanation

Explanation:
Melatonin is a hormone secreted by the pineal gland, a small endocrine gland located in the brain. Its secretion is highly sensitive to light and dark cycles, being produced in higher amounts at night. Melatonin is crucial for regulating the circadian rhythm (sleep-wake cycle), maintaining biological clocks, and influencing seasonal reproductive functions in some animals. Thymosin is from the thymus, oxytocin from the posterior pituitary.

Explanation:
Amphibians have two atria and one ventricle; mixing of blood occurs because of the single ventricle. Complete separation is achieved only in four-chambered hearts. So A true, R false.

Explanation:
Vitamin C is a cofactor for prolyl and lysyl hydroxylases, enzymes essential for collagen cross-linking and stability. Deficiency impairs wound healing and causes scurvy. Vitamin A is for epithelial integrity.