The main excretory product in humans is: MCQ with Answer and Explanation

Explanation:
Vitamin D (cholecalciferol) is synthesized in the skin from 7-dehydrocholesterol under UV-B radiation. It then undergoes activation in the liver and kidneys. It regulates calcium and phosphate metabolism.

Explanation:
Enterokinase (enteropeptidase), secreted by the duodenal mucosa, is the specific activator of pancreatic trypsinogen, converting it to active trypsin. Trypsin then activates other pancreatic zymogens (chymotrypsinogen, procarboxypeptidase). This cascade ensures that potent digestive enzymes are activated only in the intestinal lumen, preventing autodigestion of the pancreas.

Explanation:
Ethylene is a gaseous hormone that accelerates ripening, promotes leaf and fruit abscission, and senescence. Auxin and cytokinin promote growth, gibberellin elongation. Ethylene is used commercially for fruit ripening.