Final answer:
Urea is a result of amino acid catabolism. It is produced in the urea cycle, which converts ammonia to urea through steps catalyzed by different enzymes. This process is crucial for eliminating toxic ammonia from the body.
Step-by-step explanation:
Urea is the principal waste product in mammals, produced from the nitrogen originating in amino acids, and it leaves the body in urine. In the process known as the urea cycle, or sometimes the ornithine cycle, amino acid catabolism leads to the formation of ammonia, which is then converted to urea. The urea cycle involves five intermediate steps, which are catalyzed by five different enzymes. These steps begin with the conversion of ammonia to carbamoyl phosphate, which then enters the cycle. The first two steps of the urea cycle occur in the mitochondria and the last three in the cytosol. This pathway is essential for the safe elimination of toxic ammonia from the body and the concentration of urea in the blood - referred to as blood urea nitrogen or BUN - is an important indicator of kidney function.
Therefore, the correct answer to the question is: c) Amino acid catabolism.