Osmoconformers are aquatic organisms that have permeable body surfaces. Their body fluids have solute concentrations similar to those of the surrounding water. Osmoregulators include aquatic animals in coastal regions that conserve ions under some conditions and lose excess ions in others. Terrestrial animals have many adaptations to conserve water and regulate ion composition. Animals must remove wastes.
Most nitrogenous wastes come from protein breakdown and include ammonia, urea, and uric acid.
Ammonia formation requires the least energy but releases the most water. Urea requires more energy but is less toxic and helps conserve water. Uric acid requires the most energy to produce but can be excreted in an almost solid form, saving water. Animals have diverse excretory systems to remove nitrogenous wastes, including contractile vacuoles, nephridia, Malpighian tubules, and kidneys. The kidneys, each of which drains into a ureter, produce urine.