Assertion (A): All organisms are composed of cells. Reason (R): The cell is the basic unit of life. MCQ with Answer and Explanation

Explanation:
Renin is released by juxtaglomerular cells of the kidney when blood pressure drops. It starts the renin-angiotensin-aldosterone system. Note: rennin (chymosin) is in the stomach for milk digestion.

Explanation:
Charles Darwin's 1859 book 'On the Origin of Species by Means of Natural Selection' laid out the theory of evolution by natural selection. Mendel's work on heredity was published later, Wallace independently conceived natural selection but Darwin's book detailed the evidence comprehensively. Lamarck proposed earlier theories.

Explanation:
Active vitamin D (calcitriol) induces synthesis of calcium-binding proteins in the intestinal mucosa, enhancing calcium absorption. Calcium is vital for bones, teeth, blood clotting, and nerve-muscle function.