Final answer:
Urea is the most abundant solute found in human urine, as humans are ureotelic animals that convert toxic ammonia into less toxic urea for excretion.
Step-by-step explanation:
The most abundant solute found in urine is urea. In humans, nitrogenous wastes are produced from the breakdown of proteins into amino acids, which are then deaminated to form various waste products, including ammonia, ammonium ion (NH4*), urea, and uric acid. Ammonia is highly toxic and is quickly converted to urea in the liver due to its lesser toxicity. Humans primarily excrete urea, with smaller amounts of ammonium ions and very little uric acid, making them ureotelic animals. Although birds, reptiles, and some terrestrial invertebrates convert ammonia to uric acid, this conversion is more energy-intensive and complex compared to the conversion of ammonia to urea, which is the predominant process in mammals, including humans.