Blood cells showing osmosis
Cells in the human body and in the bodies of all living things behave like microscopic bags of solution housed in a semipermeable membrane. The health and indeed the very survival of a person, animal, or plant depends on the ability of the cells to maintain their concentration of solutes. The term osmosis describes the movement of a solvent through a semipermeable membrane from a less concentrated solution to a more concentrated one.
Water is sometimes called "the perfect solvent", and living tissue (for example, a human being's cell walls) is the best example of a semipermeable membrane. Osmosis has a number of life–preserving functions: it assists plants in receiving water, and is even used in kidney dialysis. In addition, osmosis can be reversed to remove salt and other impurities from water, thus maintaining salt balance.
Osmosis is essential in biological systems, as biological membranes are semipermeable. In general, these membranes are impermeable to large and polar molecules, such as ions, proteins, and polysaccharides, while being permeable to non–polar and/or hydrophobic molecules like lipids as well as to small molecules like oxygen, carbon dioxide, nitrogen, nitric oxide, etc. Permeability depends on solubility, charge, or chemistry, as well as solute size. Osmosis provides the primary means by which water is transported into and out of cells.
Cells in the human body and in the bodies of all living things behave like microscopic bags of solution housed in a semipermeable membrane. The health and indeed the very survival of a person, animal, or plant depends on the ability of the cells to maintain their concentration of solutes.