3. The human body excretes nitrogen in the form of urea, NH2CONH2. The key biochemical step in urea formation is the reaction of water with arginine to produce urea and ornithine:
(a) What is the mass percent of nitrogen in urea , arginine, and ornithine?
(b) How many grams of nitrogen can be excreted as urea when 143.2 g of ornithine is produced?