Question

Which excretory material is least toxic?

• A. Ammonia
• B. Urea
• C. Uric acid
• D. All are equally toxic

Answer 1

Answer: (C)

Uric acid

Ammonia is produced as a result of catabolism of proteins, especially in the liver cells by oxidative deamination of excess of amino acids in the presence of oxidase enzyme. It is highly toxic and must be metabolised or expelled from the body as soon as possible.
Ammonia is highly soluble in water and a very large volume of water is needed by the animal to dissolve ammonia.

1 gm of ammonia needs about 300 - 500 ml of water. But this is not a problem for animals living in an aqueous habitat which are generally found to be ammonotelic.
Urea is far less toxic than ammonia and so can remain inside the body for a long. Uric acid is less toxic than ammonia or urea; it contains four nitrogen atoms and a small amount of water is needed for its excretion. Out of solute, it precipitates and forms crystals

So, the correct answer is 'Uric acid'