Question

Terrestrial animals are generally either ureotelic or uricotelic, not ammonotelic,why?

Answer 1

The organisms which excrete urea as waste are called ureotelic. The organisms which excrete uric acid are called uricotelic whereas the organisms which excrete ammonia as waste are called ammonotelic.

Complete answer:
Excretion is the process by which the organisms remove the waste from their body. The waste is mostly nitrogen waste. According to the type of nitrogen waste organisms are divided into-
Ureotelic organisms excrete nitrogenous waste in the form of urea. Urea is less harmful and does not require much water. Example- humans
Uricotelic organisms excrete uric acid as waste. Example -birds, snakes.
Ammonotelic organisms excrete ammonia as waste. Examples of ammonotelic organisms are fishes, tadpoles of frogs, all marine animals.
Out of the three types of waste uric acid is the least poisonous and is least soluble in water followed by urea and ammonia is the most poisonous and is most soluble in water.
Terrestrial animals excrete uric acid or urea because they are less toxic and do not require water. It is also one of the methods to conserve water. Whereas, in aquatic organisms, ammonia can easily diffuse in water.

Note: The metabolic wastes rich in nitrogen are obtained by the protein metabolism. These wastes are eliminated in the form of urine or faeces from the body. The other metabolic wastes released from the body are sulphates, phosphates, carbon dioxide etc. The elimination of the waste from the organism is significant in maintaining the chemical homeostasis of the organism.