Metabolic wastes, including nitrogenous wastes, are eliminated in the animal's urine but this can cause significant water loss. Consider a beetle and a lizard. Compare and contrast how these two organisms eliminate their wastes yet minimize water loss. The kidney of a cactus wren is less efficient at concentrating urine than are the kidneys of a kangaroo rat, yet the cactus wren uses less water to rid the body of metabolic wastes, including nitrogenous wastes. Explain how this can be.
Excess salts can be particularly troublesome for desert animals for it can exacerbate dehydration.
Describe ways in which some desert animals can reduce salt intake and the unique ways that some rid themselves of excess salts. To survive periods of water deprivation, animals must store water which is gradually depleted until the body is again rehydrated. Indeed some desert animals are superb water hoarders. Describe how desert tortoises survive between drinks.