In humans, most nitrogen waste is excreted from the body in what molecular form?

The correct answer is urea because it is the primary form in which nitrogen waste is excreted by humans. The process begins in the liver, where amino acids from proteins are deaminated, producing ammonia. Ammonia is highly toxic, so it is quickly converted into urea through the urea cycle. Urea is much less toxic and can be safely transported in the bloodstream to the kidneys, where it is excreted in urine.

This method of excreting nitrogen is efficient for humans as it allows for the safe removal of waste products while conserving water, compared to other forms like ammonia which would require significant water for safe excretion. Urea's presence in urine serves as a key indication of the body’s protein metabolism and waste management.