Question

All birds and mammals are capable of osmoregulation

Answer 1

Answer:

Osmoregulation, the control of water and salt balance, presents different challenges to organisms living in fresh water, salt water, and aerial or terrestrial environments (Fig. 6.1). Many structures and organs are involved in osmoregulation, including the skin, gills, digestive tract, cloaca, kidneys, and bladder. In fresh water, an amphibian or reptile is hyperosmotic. The ionic concentration of the body is greater than that of the environment, and, if not regulated, water moves in, cells swell and possibly burst, and ions become too dilute. Excessive hydration can be avoided in several ways. Permeability of the skin can be decreased or urinary output can be increased, although salts must be conserved. Marine or brackish species face the opposite challenge. They are hyposmotic in relation to their environment. The ionic concentration of the body is less than that of the environment; thus, water moves out if unregulated, causing dehydration and a concentration of salts in the body fluid. Dehydration can be circumvented by decreasing permeability of skin and reducing the amount of water in urine, although nitrogenous waste must still be removed before reaching toxic levels. Terrestrial species are also at risk of dehydration, but from evaporation rather than osmotic loss of water. They counteract this problem physiologically in a manner similar to marine species. The basic physics of water loss and gain is rather simple, but the mechanisms by which amphibians and reptiles accomplish osmoregulation are varied and often complex