Question

Arrange the following in correct order based on increasing toxicity-
(a) Urea
(b) Uric acid
(c) Ammonia

A. a-b-c
B. b-a-c
C. c-a-b
D. c-b-a

Answer 1

Animal waste which contains high nitrogen content materials. Through the use of the activity of the kidneys, the same organ involved in maintaining water balance, nitrogenous waste is eliminated from body fluids.

Complete answer:
The metabolism process in an organism takes place as an important biological mechanism. The food eaten by the organism is digested through the metabolic process and the waste materials are produced. These waste materials are nitrogenous in nature. The presence of nitrogenous wastes are necessary to be eliminated through the body in the form of ammonia, urea and urine.
In animals, the nitrogenous wastes produced in the body are excreted in three forms which are ammonia, uric acid and urea. Ammonia is the most poisonous of all the different nitrogenous wastes and it is highly toxic in nature. It alters the pH of the body by increasing it. The formation and production of ammonia utilises high energy and uses ATP as energy source. In order to exit ammonia from the body, it requires large quantities of water as it has to be dilute to a great extent.
Ammoniotelic are marine species including protozoans, crustaceans, poriferans, fish where water is not a restriction. Urea requires a relatively greater amount of energy and is less harmful in nature. Animals that excrete nitrogenous waste in urea form are referred to as ureotelic. Urea is less toxic than ammonia.
In terrestrial animals, water conservation is an important requirement and due to this condition, ammonia is converted into uric acid in the liver and for excretion it is converted into a less toxic form which is urea.
Uric acid is the least soluble and the least toxic form of all the nitrogenous wastes. It does take a significant amount of energy and uses the least amount of water for excretion. It forms when purine-called chemicals break down. Purines are present in the body as a natural material. In the body, they can also be produced when DNA is broken down. The least toxic to the body of all is uric acid.

Hence, the correct answer is option (B).

Note: In the degradation of proteins by cells, nitrogenous waste products are produced. To obtain energy, cells catabolize amino acids and the process of deamination is the first phase of this procedure. The excretion of nitrogen waste takes place by the excretion of ammonia, urea and uric acid. By converting ammonia to a relatively non-toxic form, such as urea or uric acid, animals must detoxify ammonia. The most toxic form is ammonia, followed by urea and uric acid.