List three main nitrogenous waste products compare their toxicity and the amount of water that must be expelled in order to excrete each one?

Answer 1

The three main nitrogenous waste products are Ammonia, Urea and Uric Acid. Ammonia can only be tolerated at very low concentratisons, animals that excrete nitrogenous wastes as ammonia need access to lots of water. In this case ammonie excretion is most common in aquatic species. The ammonia molecules easily pass through membranes and are readily lost by diffusion to the watter surrounding the aquatic animal. In most vertebrates the ammoina release happens all across the whole body surface. In fishes, the ammonia is lost as ammonium ions (HH4+) across the epithelium of the gills. The kidneys excreet only minor amounts of the nitrogenous wastes. In freshwater fishes, the gille epithelium takes up Na+ from the water in exchange for NH4+, which helps to maintain a muchg higher Na+ concentration in the body fluids than in the surroundng water. Next we look at Urea, mammals, adult amphibians, sharks, and turtles excrete urea. This substance is produced in the vertebrate liver by a metabolic cycle that combines ammonia with carbon dioxide. Urea has a low toxicity, about 100,000 times less than that of ammonia. This allowes animals to transport and store urea safely at high concentrations. One of thie disadvantages of urea is that the animals must expand thir engergy to produce it from ammonia. Urea excretion requires much less water, becausemuch less water is lost when a given quantity of nitrogen is exvreted in a concentrates solution of urea rather than a dilute solution of ammonia. Insects, land snails, many reptiles, and birds, excrete uric acid. Urea and uric acid are like But unlike ammonia or urea, uric acid is largely insoluble in water and can be excreted as a semi solid paste with very little water loss. Uric acid is even more energetically expensive to produce than urea, requiring considerable ATP for synthesis from ammonia.