Concept:Urea is a nitrogenous waste product formed primarily from the breakdown of proteins in the liver.
Explanation:Proteins are composed of amino acids.
During protein metabolism, amino acids undergo deamination, releasing ammonia (
NH3​).
Ammonia is highly toxic to the body.
The liver converts ammonia into urea (
CH4​N2​O, also called carbamide) through the ornithine cycle.
This process combines ammonia with carbon dioxide (
CO2​).
Urea is water‑soluble and less toxic.
It dissolves in blood and is filtered by the kidneys.
Finally, urea is excreted in urine.
Carbohydrates and lipids do not contain nitrogen.
Hence, they do not produce urea as a metabolic end product.
Only the metabolism of proteins (which contain nitrogen) leads to urea formation.
Answer:Proteins
