ABSTRACT
Ammonia excretion There is no store for nitrogen-containing compounds as there is for carbohydrate (glycogen, Section J6) or lipids (triacylglycerol, Section K4). Thus nitrogen ingested in excess of what is required by the organism has to be excreted. The excess nitrogen is first converted into ammonia and is then excreted from living organisms in one of three ways. Many aquatic animals simply excrete the ammonia itself directly into the surrounding water. Birds and terrestrial reptiles excrete the ammonia in the form of uric acid, while most terrestrial vertebrates convert the ammonia into urea before excretion. These three classes of organisms are called: ammonotelic, uricotelic and ureotelic, respectively.
