If early tetrapods lived in freshwater, and if they lost the ability to produce urea and used ammonia only, they would have to evolve it from scratch again later.

This enzyme controls the final step of the urea cycle, which produces urea by removing nitrogen from arginine.

The liver produces urea in the urea cycle as a waste product of the digestion of protein.

Another nitrogen is added from aspartate, producing the denitrogenated fumarate, and the resulting arginine (a guanidinium compound) is hydrolysed back to ornithine, producing urea.

It produces anhydrous ammonia and granular urea, and is one of the largest urea plants in Asia.

Since urea production is performed on a worldwide basis, plants producing urea would be able to expand their capacity if needed.

The plant, completed in 1985, produces ammonia, methanol and urea for export.

Excess ammonia is processed in the liver through the urea cycle to produce urea.

Another disadvantage is the fact that fossil fuels are used to produce urea.

Ammonium cyanate decomposes to ammonia and cyanic acid which in turn react to produce urea in a nucleophilic addition followed by tautomeric isomerization: