1 History 2 Mechanism 3 Factors
3.1 Osmotic pressure 3.2 Osmotic gradient
4.1 Reverse osmosis 4.2 Forward osmosis
5 See also 6 References 7 External links
The "endosmometer" invented by Dutrochet.
Formation of Traube cells. Crystals of potassium ferrocyanide are put into a solution of copper sulfate (left). The interaction between them forms a film of potassium ferrocyanide at the vassel wall (right). The film is slowly filled with water inside it due to osmosis, like a membrane of a plant cell.
Some kinds of osmotic flow has been observerd since ancient times,
e.g., on the construction of Egyptian pyramids. Jean-Antoine Nollet
first documented observation of osmosis in 1748. The word "osmosis"
descends from the words "endosmose" and "exosmose", which were coined
by French physician René Joachim
Henri Dutrochet (1776–1847) from
the Greek words ἔνδον (éndon “within”), ἔξω (éxō
“outer, external”), and ὠσμός (ōsmós "push,
impulsion"). In 1867,
Moritz Traube invented highly selective
precipitation membranes, advancing the art os measurement of osmotic
When the membrane has a volume of pure water on both sides, water molecules pass in and out in each direction at exactly the same rate. There is no net flow of water through the membrane. The mechanism responsible for driving osmosis has commonly been represented in biology and chemistry texts as either the dilution of water by solute (resulting in lower concentration of water on the higher solute concentration side of the membrane and therefore a diffusion of water along a concentration gradient) or by a solute's attraction to water (resulting in less free water on the higher solute concentration side of the membrane and therefore net movement of water toward the solute). Both of these notions have been conclusively refuted. The diffusion model of osmosis is rendered untenable by the fact that osmosis can drive water across a membrane toward a higher concentration of water. The "bound water" model is refuted by the fact that osmosis is independent of the size of the solute molecules—a colligative property—or how hydrophilic they are.
Effect of different solutions on blood cells
Micrographs of osmotic pressure on red blood cells(RBC)
Plant cell under different environments.
It is hard to describe osmosis without a mechanical or thermodynamic
explanation, but basically, there is an interaction between the solute
and water that counteracts the pressure that otherwise free solute
molecules would exert. One fact to take note of is that heat from the
surroundings is able to be converted into mechanical energy (water
Many thermodynamic explanations go into the concept of chemical
potential and how the function of the water on the solution side
differs from that of pure water due to the higher pressure and the
presence of the solute counteracting such that the chemical potential
remains unchanged. The virial theorem demonstrates that attraction
between the molecules (water and solute) reduces the pressure, and
thus the pressure exerted by water molecules on each other in solution
is less than in pure water, allowing pure water to "force" the
solution until the pressure reaches equilibrium.
If the medium is hypotonic relative to the cell cytoplasm — the cell will gain water through osmosis. If the medium is isotonic — there will be no net movement of water across the cell membrane. If the medium is hypertonic relative to the cell cytoplasm — the cell will lose water by osmosis.
Essentially, this means that if a cell is put in a solution which has
a solute concentration higher than its own, it will shrivel, and if it
is put in a solution with a lower solute concentration than its own,
the cell will swell and may even burst.
Chemical gardens demonstrate the effect of osmosis in inorganic
Main article: Osmotic pressure
As mentioned before, osmosis may be opposed by increasing the pressure
in the region of high solute concentration with respect to that in the
low solute concentration region. The force per unit area, or pressure,
required to prevent the passage of water through a selectively
permeable membrane and into a solution of greater concentration is
equivalent to the osmotic pressure of the solution, or turgor. Osmotic
pressure is a colligative property, meaning that the property depends
on the concentration of the solute, but not on its identity. It also
is involved in facilitated diffusion.
The osmotic gradient is the difference in concentration between two
solutions on either side of a semipermeable membrane, and is used to
tell the difference in percentages of the concentration of a specific
particle dissolved in a solution.
Usually the osmotic gradient is used while comparing solutions that
have a semipermeable membrane between them allowing water to diffuse
between the two solutions, toward the hypertonic solution (the
solution with the higher concentration). Eventually, the force of the
column of water on the hypertonic side of the semipermeable membrane
will equal the force of diffusion on the hypotonic (the side with a
lesser concentration) side, creating equilibrium. When equilibrium is
reached, water continues to flow, but it flows both ways in equal
amounts as well as force, therefore stabilizing the solution.
Main article: Reverse osmosis
Oxford English Dictionary
Original text : Avant que de finir ce Mémoire, je crois devoir rendre compte d'un fait que je dois au hasard, & qui me parut d'abord … singulier … j'en avois rempli une fiole cylindrique, longue de cinq pouces, & d'un pouce de diamètre ou environ ; & l'ayant couverte d'un morceau de vessie mouillée & ficelée au col du vaisseau, je l'avois plongée dans un grand vase plein d'eau, afin d'être sûr qu'il ne rentrât aucun air dans l'esprit de vin. Au bout de cinq ou six heures, je fus tout surpris de voir que la fiole étoit plus pleine qu'au moment de son immersion, quoiqu'elle le fût alors autant que ses bords pouvoient le permettre ; la vessie qui lui servoit de bouchon, étoit devenue convexe & si tendue, qu’en la piquant avec une épingle, il en sortit un jet de liqueur qui s'éleva à plus d'un pied de hauteur.
Translation : Before finishing this memoir, I think I should report an event that I owe to chance and which at first seemed to me … strange … I filled [with alcohol] a cylindrical vial, five inches long and about one inch in diameter; and [after] having covered it with piece of damp bladder [which was] tied to the neck of the vial, I immersed it in a large bowl full of water, in order to be sure that no air re-entered the alcohol. At the end of 5 or 6 hours, I was very surprised to see that the vial was fuller than at the moment of its immersion, although it [had been filled] as far as its sides would allow ; the bladder that served as its cap, bulged and had become so stretched that on pricking it with a needle, there came from it a jet of alcohol that rose more than a foot high.
^ Etymology of "osmosis" :
Henri Dutrochet, L'Agent Immédiat du Movement Vital Dévoilé dans sa Nature et dans son Mode d'Action chez les Végétaux et chez les Animaux [The immediate agent of living movement, its nature and mode of action revealed in plants and animals] (Paris, France: Dentu, 1826), pp. 115 and 126. The intermediate word "osmose" and the word "osmotic" were coined by Scottish chemist Thomas Graham. See: Thomas Graham (1854) "VII. The Bakerian Lecture – On Osmotic Force," Philosophical Transactions of the Royal Society (London), vol. 144, pp. 177–288; see especially pp. 177, 178, and 227. See also: Thomas Graham and Henry Watts, Elements of Chemistry: Including the Applications of the Sciences in the Arts, 2nd ed. (London, England: Hippolyte Bailliere, 1858), vol. 2, p. 616. The word "osmosis" first appeared in: Jabez Hogg, The Microscope: Its History, Construction, and Application..., 6th ed. (London, England: George Routledge and Sons, 1867), p. 226. The etymology of the word "osmosis" is discussed in: Homer W. Smith (1960). "I. Theory of Solutions: A knowledge of the laws of solutions" (PDF). Circulation. 21: 808–817 (810). doi:10.1161/01.CIR.21.5.808.
^ Kramer, Eric; David Myers. "
Look up osmosis in Wiktionary, the free dictionary.
The Wikibook School Science has a page on the topic of: Osmosis demonstration
Wikimedia Commons has media related to Osmosis.