Conversion of ammonia to urea is done by ______ cycle.
A. Ornithine
B. Arginine
C. Fumaric
D. Citrulline

Hint: We have to know that in nearly $80\% $ of the nitrogen excreted by humans and mammals is in the form of urea, formed by a series of reactions occurring in the liver cell cytosol and mitochondrial matrix. T. Ammonia is a harmful result of the metabolism of nitrogen that should be eliminated from our bodies.

Complete answer:
We have to know that the urea cycle or ornithine cycle in the mitochondria of liver cells converts surplus ammonia into urea. The urea forms, is purified by the kidneys, then enters the circulatory system, and is ultimately excreted in the urine.The comprehensive answer to the formation of urea from ammonia is as follows:
$2Ammonia + C{O_2} + 3ATP \to Urea + Water + 3ADP$
In humans and mammals, urea is the main end product of nitrogen metabolism. The product of oxidative deamination reactions, ammonia, is poisonous in even small quantities and must be extracted from the body. The conversion reactions of ammonia into urea are described by the urea cycle or ornithine cycle. The urea is then transferred to the kidneys, where it is excreted, as these reactions occur in the liver.Hence, option A is the right option.



Hence, the correct answer is option (A).

Note: The main aim of the cycle of ornithine is to eliminate the body from toxic ammonia. Every day, roughly $10g$ to $20g$ of ammonia is eliminated from the body of a healthy adult. A period of dysfunctional urea will mean that the body has an excess amount of ammonia that can contribute to hyperammonemia and associated diseases. The deficiency in the urea cycle of one or more of the main enzymes that catalyze different reactions may cause cycle-related disorders.