Question

Urea and uric acid are _________

Answer 1

Hint: Terrestrial organisms are adapted to convert toxic nitrogenous wastes that are excreted by fishes into non-toxic forms and in mammals they are used in the concurrent mechanisms.

Complete answer:
The primary producers of urea are mammals, including humans, so they are called ureotelic animals. For the metabolism of nitrogen-containing compounds, urea plays an important role. Urea is one of the main nitrogen-containing substances in animal urine. It is colorless, odorless, and highly soluble in water and when compared to ammonia and uric acid it is less toxic. It is widely used as fertilizer as it is rich in nitrogen-containing substances. Urea is also found in the urine of amphibians and some fishes. Urea also plays an important role in the countercurrent mechanism in nephrons that are used to prevent loss of water and maintain blood pressure. In animals including human beings, urea is produced from ammonia in the liver.
${ 2NH }_{ 3 }+{ CO }_{ 2 }+{ H }_{ 2 }O\longrightarrow { H }_{ 2 }N-{ CO }-{ NH }_{ 2 }+{ 2ADP+{ 4Pi+{ AMP } } }$
Uric acid is the nitrogenous waste produced in the body of birds and reptiles. They convert ammonia into uric acid or guanine instead of urea. So, they are called uricotelic organisms.

Additional information:
- Proteins and nucleic acids are the two important macromolecules in the body that contain nitrogen.
- During the breakdown of these molecules, carbon, hydrogen, and oxygen are stored in carbohydrates and fats and these nitrogenous wastes form into ammonia by using ATP. fishes can easily excrete ammonia whereas terrestrial animals such as birds and reptiles are adapted to convert ammonia into uric acid and mammals convert ammonia into urea.

Note: Compared to urea and uric acid ammonia is the most toxic form of nitrogenous wastes, so terrestrial organisms detoxify ammonia by converting into non-toxic forms such as urea and uric acid.