Final answer:
Nitrogenous wastes such as urea are produced during protein catabolism. Ammonia, a toxic byproduct, is quickly converted into urea in the liver, which is then excreted by the kidneys. Urea serves to lower the toxicity of nitrogen waste and aids in water reabsorption within the kidneys.
Step-by-step explanation:
Nitrogenous wastes are inevitable byproducts of protein catabolism, or the breakdown of proteins into their constituent amino acids. These amino acids are then deaminated, which means the nitrogen-containing amino group (NH₂) is removed, resulting in the formation of substances like ammonia (NH₃), ammonium ion (NH₄+), urea, and uric acid. The most common form of nitrogen waste in humans is urea, which is created in the liver through the urea cycle and subsequently excreted by the kidneys.
Ammonia, which is highly toxic, is rapidly transformed into urea, a less harmful compound. Urea not only reduces toxicity but also plays a role in water reabsorption in the kidneys. While aquatic animals can often excrete ammonia directly into their environment, terrestrial animals, including humans, must convert it into urea or uric acid to avoid toxicity. The excretion of these compounds is a critical function of the kidneys, and inefficiency in this process can lead to increased toxicity within the body, a condition known as uremia. Additionally, urea is widely used as a fertilizer due to its high nitrogen content.