What do urea, proteins, and amino acids classify as?

Urea, proteins, and amino acids are classified as nitrogenous compounds due to their significant content of nitrogen. The presence of nitrogen is a key characteristic that distinguishes these compounds from non-nitrogenous substances. Urea is a waste product formed from the breakdown of proteins and is primarily comprised of nitrogen, while proteins are large macromolecules made up of amino acids that contain nitrogen in their structure. Amino acids, the building blocks of proteins, also contain an amine group (-NH2), which includes nitrogen. This nitrogenous nature is fundamental to their classification, making them essential for various biological functions, including the synthesis of hormones and enzymes, as well as their role in cellular metabolism.

This understanding of nitrogenous compounds is crucial in contexts related to sanitation and environmental impacts, as nitrogen can influence processes such as water quality and nutrient cycling. The other options—non-nitrogenous compound, odour, and all of the above—do not accurately describe the nature of urea, proteins, and amino acids in this context.