Class 11 NEET Biology Excretory Products and Their Elimination

(a) Urea NH2−CO−NH2 is formed from two molecules of ammonia and one molecule of carbon dioxide. A molecule of ammonia combines with carbondioxide to form carbonyl phosphate. It reacts with ornithine to form citrulline. Citrulline accepts another molecule of NH4+ giving rise to arginine. Arginine is hydrolysed into urea and ornithine with the help of enzyme arginase.