Also found in: Dictionary, Thesaurus, Medical, Legal, Acronyms, Wikipedia.
Related to osmosis: reverse osmosis, diffusion


(ŏzmō`sĭs), transfer of a liquid solvent through a semipermeable membrane that does not allow dissolved solids (solutes) to pass. Osmosis refers only to transfer of solvent; transfer of solute is called dialysisdialysis
, in chemistry, transfer of solute (dissolved solids) across a semipermeable membrane. Strictly speaking, dialysis refers only to the transfer of the solute; transfer of the solvent is called osmosis.
..... Click the link for more information.
. In either case the direction of transfer is from the area of higher concentration of the material transferred to the area of lower concentration. This spontaneous migration of a material from a region of higher concentration to a region of lower concentration is called diffusiondiffusion,
in chemistry, the spontaneous migration of substances from regions where their concentration is high to regions where their concentration is low. Diffusion is important in many life processes.
..... Click the link for more information.

Principles of Osmosis

Osmosis will occur if a vessel is separated into two compartments by a semipermeable membrane, both compartments are filled to the same level with a solvent, and solute is added to one side. The level of the liquid on the side containing the solute will rise as the solvent flows from the side of its higher concentration to the side of lower concentration. If an external pressure is exerted on the side containing the solute, the transfer of solvent can be stopped and even reversed (reverse osmosis). Two solutions separated by a semipermeable membrane are said to be isotonic if no osmosis occurs. If osmosis occurs, transfer of solvent is from the hypotonic solution to the hypertonic solution, which has the higher osmotic pressure.

The minimum pressure necessary to stop solvent transfer is called the osmotic pressure. Since the osmotic pressure is related to the concentration of solute particles, there is a mathematical relationship between osmotic pressure, freezing-point depression, and boiling-point elevation. Properties such as osmotic pressure, freezing point, and boiling point, which depend on the number of particles present rather than on their size or chemical nature, are called colligative properties. For dilute solutions the mathematical relationship between the osmotic pressure, temperature, and concentration of solute is much like the relation between pressure, temperature, and volume in an ideal gas (see gas lawsgas laws,
physical laws describing the behavior of a gas under various conditions of pressure, volume, and temperature. Experimental results indicate that all real gases behave in approximately the same manner, having their volume reduced by about the same proportion of the
..... Click the link for more information.
). A number of theories explaining osmotic pressure by analogy to gases have been devised, but most have been discarded in favor of thermodynamic interpretations using such concepts as the entropy of dilution.

Biological Importance of Osmosis

Osmosis and dialysis are of prime importance in living organisms, where they influence the distribution of nutrients and the release of metabolic waste products. Living cells of both plants and animals are enclosed by a semipermeable membrane called the cell membrane, which regulates the flow of liquids and of dissolved solids and gases into and out of the cell. The membrane forms a selective barrier between the cell and its environment; not all substances can pass through the membrane with equal facility. Without this selectivity, the substances necessary to the life of the cell would diffuse uniformly into the cell's surroundings, and toxic materials from the surroundings would enter the cell.

If blood cells (or other cells) are placed in contact with an isotonic solution, they will neither shrink nor swell. If the solution is hypertonic, the cells will lose water and shrink (plasmolyze). If the solution is hypotonic (or if pure solvent is used) the cells will swell; the osmotic pressure that is developed may even be great enough to rupture the cell membrane. Saltwater from the ocean is hypertonic to the cells of the human body; the drinking of ocean water dehydrates body tissues instead of quenching thirst.

In plants osmosis is at least partially responsible for the absorption of soil water by root hairs and for the elevation of the liquid to the leaves of the plant. However, plants wilt when watered with saltwater or treated with too much fertilizer, since the soil around their roots then becomes hypertonic.



the passage of a substance, usually a solvent, through a semipermeable membrane that separates a solution from a pure solvent or two solutions of different concentrations from each other. A semipermeable membrane allows small molecules of a solvent to pass through but is impermeable to larger molecules. The concentrations on both sides of such a membrane can be equalized only by unilateral diffusion of the solvent. Hence, osmosis always proceeds from a pure solvent to a solution or from a dilute solution to a more concentrated one. Osmosis within an enclosed volume of liquid is called endosmosis, and osmosis to the outside is called exosmosis.

A solvent is transported through a membrane by osmotic pressure, which is equal to the excess external pressure that has to be exerted by the solution in order to stop osmosis, that is, to create the condition of osmotic equilibrium. Excess pressure above the osmotic pressure may lead to reversal of osmosis, or reverse diffusion, of the solvent. In cases where a membrane is permeable not only to a solvent but also to some dissolved substances, diffusion of the solutes from the solution into the solvent is called dialysis, which is used to separate polymers and colloidal systems from low-molecular admixtures.

Osmosis was first observed by J. A. Nollet in 1748 but was not thoroughly studied until a century later. A major factor in biological processes, it is widely used in laboratory work to study various biological structures and to determine the molecular characteristics of polymers and the concentration of solutions. Osmotic phenomena are sometimes utilized in industry, for example, to produce certain polymeric materials or to purify highly mineralized water by reverse osmosis.



(physical chemistry)
The transport of a solvent through a semipermeable membrane separating two solutions of different solute concentration, from the solution that is dilute in solute to the solution that is concentrated.


1. the passage of a solvent through a semipermeable membrane from a less concentrated to a more concentrated solution until both solutions are of the same concentration
2. diffusion through any membrane or porous barrier, as in dialysis
References in periodicals archive ?
Forward osmosis or 'manipulated osmosis' or just 'osmosis' are terms used to describe a natural phenomenon, whereby a solvent flows from a region of lower osmotic pressure across a selectively permeable membrane to an area of higher osmotic pressure.
Before installing Reverse Osmosis Plant, the ground water is the main source for various leather processing operations.
In keeping with its commitment to organise a CygreenCO Olympics, three water reuse projects at Beijing employ more than 5,000 FILMTECao 8-inch diameter reverse osmosis (RO) membrane elements.
Nonetheless, Pedersen cautions that it's too early to recommend that all reclaimed wastewater facilities employ reverse osmosis.
Osmosis caused water to move from the less salty water to the saltier fish.
The use of reverse osmosis (RO), for example, can greatly reduce or eliminate the need for ion exchange regenerant in the production of boiler feedwater makeup.
AMERICAN pop princess Brandy is one of a host of stars who lend their vocal talents to the hilarious animated movie Osmosis Jones.
Osmosis, based on Liverpool's Brunswick Business Park, supplies fresh flowers to homes and businesses throughout the UK, and recently brought out its winter range of flowers.
Labs that require only small amounts of highly purified water and that lack the space and funds for a reverse osmosis and Type I reagent grade water purification system will be attracted to the Aqua RODI-C compact water system, according to the manufacturer.
This paper argues that instruction in the conventions of genres in which students must write is a necessary element of university teaching and learning: it empowers students in theft journey into academia and into disciplines, it allows them to sidestep the slow process of osmosis, and to make the most of their intellectual potential.
Hydration Technology Innovations, LLC (HTI), the world's only manufacturer of commercially viable Forward Osmosis (FO) membranes, announces the production of a new highly durable, dimensionally stable, thin film composite membrane as the most recent addition to the OsMem[TM] FO membrane line.