Final answer:
An organism that excretes ammonia or ammonium ion as the principal nitrogenous waste is called ammonotelic. Aquatic animals tend to be ammonotelic, while terrestrial animals convert nitrogenous waste into less toxic substances, such as urea or uric acid, becoming ureotelic or uricotelic respectively.
Step-by-step explanation:
An organism that secretes ammonia or ammonium ion as the principal nitrogenous waste is considered to be ammonotelic. Nitrogenous wastes are byproducts of the metabolism of nitrogen-containing compounds like proteins and nucleic acids. Ammonia is a very toxic compound and needs to be excreted or converted to less toxic compounds. Ammonotelic animals, generally aquatic organisms, excrete ammonia directly into their environment. In contrast, terrestrial animals have developed different strategies for dealing with nitrogenous wastes, converting ammonia into urea or uric acid through the urea cycle. Animals that secrete urea as the principal nitrogenous waste are termed ureotelic, which includes mammals like humans, while animals that convert ammonia into uric acid, typically birds and reptiles, are referred to as uricotelic.