Osmosis in the movement of water molecules through a selectively permeable membrane. It occurs from a region of high water concentration to a region of low water concentration. The control of water balance in animals is known as osmoregulation. Osmoregulation is a homeostatic mechanism. The body fluids of a salt water fish are hypotonic (higher in water concentration) compared with the surrounding sea water - the sea water is therefore hypertonic. Because of this they constantly lose water by osmosis through its selectively permeable gill and gut membranes. …
