Question

Which of the following is a metabolism waste of protein metabolism?
(a) Ammonia, urea and carbon dioxide
(b) Urea, oxygen and nitrogen
(c) Urea, ammonia and alanine
(d) Urea, Ammonia and creatinine

Answer 1

Hint: The first compound is also called carbamide. The second compound is a colourless gas, made up of nitrogen and hydrogen. The third compound is a waste product formed in the muscles after the breakdown of creatine.

Complete answer:
Urea, ammonia and creatinine are metabolic waste products in protein metabolism. ‘Metabolic wastes’ also called ‘excrements’, are substances that are formed as by-products in the metabolic processes. These cannot be utilised by the organism and when accumulated in surplus can be toxic. Hence they must be excreted out.
So, one may wonder what the examples of metabolic wastes are.
Nitrogenous compounds, carbon dioxide, water, salts like phosphates, sulphates etc are some examples of them. The nitrogen-containing compounds through which excess nitrogen is released are called ‘nitrogenous waste’. Examples of them are ammonia, urea, uric acid and creatinine. All of them collectively form the metabolic waste in protein metabolism.
Elimination of metabolic waste: All the metabolic wastes are excreted from the body in the form of water solutes. Excretory organs including nephridia, malpighian tubules, kidneys participate in their elimination from the body. However, gaseous waste like carbon dioxide along with water vapour is excreted through the lungs.
So, the correct answer is, ‘Urea, Ammonia and creatinine’.

Note:
- ‘Protein metabolism’ represents the several biochemical processes that result in the synthesis of proteins and amino acids called anabolism, and also the breakdown of proteins called catabolism.
- Carbon is a metabolic waste of cellular respiration.
- Significance of elimination of metabolic waste: This whole process is essential to maintain the chemical homeostasis of the body.