The organ that produces urea as the main nitrogenous waste in humans is the: MCQ with Answer and Explanation

Explanation:
Glucagon is secreted by alpha cells of the islets of Langerhans when blood glucose is low. It acts on the liver to stimulate glycogenolysis (glycogen to glucose) and gluconeogenesis (synthesis of glucose from non-carbohydrates), thereby increasing blood glucose. Insulin, from beta cells, lowers blood glucose. Somatostatin inhibits both.

Explanation:
Edward Jenner, an English physician, is known as the 'father of immunology'. In 1796, he developed the world's first successful vaccine against smallpox. He observed that milkmaids who had contracted cowpox (a mild disease) were immune to smallpox. He inoculated a boy with material from a cowpox blister, successfully conferring immunity to smallpox, thus pioneering the concept of vaccination.

Explanation:
During photosynthesis, water is split (photolysis), releasing oxygen as a byproduct. Respiration consumes oxygen, nitrogen fixation uses nitrogenase, transpiration releases water vapor.