Final answer:
To prevent fish from dying due to ammonia, beneficial bacteria in the nitrogen cycle convert ammonia into nitrite and then into the less toxic nitrate. Mammals, reptiles, and some invertebrates have different mechanisms to convert toxic ammonia into less harmful substances like urea and uric acid for excretion.
Step-by-step explanation:
Ammonia Metabolism in Aquatic Animals
In aquatic environments, fish excrete toxic ammonia as a waste product, which is derived from the deamination of amino acids. However, to prevent their fish from dying due to the accumulated ammonia in their habitats, which could quickly be fatal, a process called the nitrogen cycle is crucial. The nitrogen cycle in a well-maintained aquarium involves beneficial bacteria that convert harmful ammonia (NH3) into nitrite, and then other bacteria convert nitrite into the less toxic nitrate. This process is essential to keep fish healthy.
Mammals, including humans, converting ammonia into urea for excretion, which is far less toxic, and can be removed from the body with less water. This is accomplished by the urea cycle. On the other hand, reptiles and many terrestrial invertebrates produce uric acid as a waste product of protein metabolism. Both urea and uric acid are far less toxic than ammonia and represent stable ways to store nitrogen before it is excreted. Aquatic animals depend on diluting ammonia in their environment or converting it into less toxic substances through physiological processes.