Biology » The Excretory System » Nitrogenous Wastes

Summarizing Nitrogenous Wastes


Ammonia is the waste produced by metabolism of nitrogen-containing compounds like proteins and nucleic acids. While aquatic animals can easily excrete ammonia into their watery surroundings, terrestrial animals have evolved special mechanisms to eliminate the toxic ammonia from their systems. Urea is the major byproduct of ammonia metabolism in vertebrate animals. Uric acid is the major byproduct of ammonia metabolism in birds, terrestrial arthropods, and reptiles.



compound made of one nitrogen atom and three hydrogen atoms


describes an animal that excretes ammonia as the primary waste material


agent that prevents cell destruction by reactive oxygen species

blood urea nitrogen (BUN)

estimate of urea in the blood and an indicator of kidney function

urea cycle

pathway by which ammonia is converted to urea


describes animals that secrete urea as the primary nitrogenous waste material

uric acid

byproduct of ammonia metabolism in birds, insects, and reptiles

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