What is urine primarily composed of?

Urine is primarily composed of urea and other dissolved substances, which is why this choice is correct. Urea, a waste product formed from the breakdown of proteins, is the most abundant nitrogenous compound in urine. It plays a critical role in the elimination of excess nitrogen from the body.

In addition to urea, urine contains a variety of dissolved substances including creatinine, uric acid, electrolytes (like sodium, potassium, chloride), and other metabolic byproducts. The composition of urine can vary based on factors such as hydration status, dietary intake, and metabolic changes. This diverse array of constituents reflects the body's ongoing processes of filtration and excretion.

The other choices do not accurately represent the primary composition of urine. While glucose and electrolytes are present in urine, they do not constitute its primary component. Normal urine does not typically contain significant amounts of proteins or fats, and the presence of red and white blood cells indicates a pathological condition rather than a standard component of urine. Thus, the correct answer emphasizes the presence of urea and the other dissolved substances fundamental to urine’s role in bodily waste elimination.