Major component of urine is A) Urea B) Sodium C) Water D) None of these
Hint: Urine is the liquid by-product of metabolism in humans and other animals. Cellular metabolism generates many by-products rich in nitrogen and must be cleared from the bloodstream, such as urea, uric acid, and creatinine. This cleansing is undertaken by urination.
Complete Answer: In humans, soluble wastes are excreted primarily by the urinary system which consists of the kidneys, ureters, urinary bladder, and urethra. The system produces urine by a combination of filtration, reabsorption and tubular secretion. About $91-96\%$ of urine consists of water. The total solids in urine is 59gm per person per day on an average. Organic matter makes up between $65\%$ and $85\%$ of urine with volatile solids comprising $75–85\%$ of the total solids. Urea is the largest constituent of the solids in urine, constituting more than $50\%$ of the total. Thus, option (A) is the correct answer. On an elemental level, human urine contains 6.87 g/L carbon, 8.12 g/L nitrogen, 8.25 g/L oxygen, and 1.51 g/L hydrogen. Their exact proportions vary with factors such as diet and health.
Note: Urine also contains a mixed bag of inorganic salts and organic compounds that includes proteins, hormones and a wide range of metabolites. These vary according to what is introduced into the body. Presence of protein in urine is cause for medical concern.