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Encyclopedia > Osmosis

Osmosis is the spontaneous net movement of water across a semipermeable membrane from a region of low solute concentration to a solution with a high solute concentration, down a solute concentration gradient. It is a physical process in which a solvent moves, without input of energy, across a semi permeable membrane (permeable to the solvent, but not the solute) separating two solutions of different concentrations.[1] Osmosis releases energy, and can be made to do work, as when a growing tree-root splits a stone. Scheme of semipermeable membrane during hemodialysis, where red is blood, blue is the dialysing fluid, and yellow is the membrane. ...

Computer simulation of the process of osmosis
Computer simulation of the process of osmosis

Net movement of solvent is from the less-concentrated (hypotonic) to the more-concentrated (hypertonic) solution, which tends to reduce the difference in concentrations. This effect can be countered by increasing the pressure of the hypertonic solution, with respect to the hypotonic. The osmotic pressure is defined to be the pressure required to maintain an equilibrium, with no net movement of solvent. Osmotic pressure is a colligative property, meaning that the property depends on the molar concentration of the solute but not on its identity. Osmosis is the result of diffusion across a semi-permeable membrane. Download high resolution version (1214x898, 83 KB)This is a screen shot from a three dimensional computer simulation of the process of osmosis. ... Download high resolution version (1214x898, 83 KB)This is a screen shot from a three dimensional computer simulation of the process of osmosis. ... This article does not cite any references or sources. ... Effect of different solutions on blood cells Plant cell under different environments In biology, a hypertonic cell environment has a higher concentration of solutes than inside the animal or plant cell. ... This article or section does not adequately cite its references or sources. ... This article is about pressure in the physical sciences. ... In chemistry, colligative properties are factors that determine how the properties of a bulk liquid solution change depending on the concentration of the solute in the bulk solution. ... For other uses, see Concentration (disambiguation). ... diffusion (disambiguation). ...


Osmosis is important in biological systems as many biological membranes are semipermeable. In general, these membranes are impermeable to organic solutes with large molecules, such as polysaccharides, while permeable to water and small, uncharged solutes. Permeability may depend on solubility properties, charge, or chemistry as well as solute size. Water molecules travel through the plasma cell membrane, tonoplast (vacuole) or protoplast in two ways. Either by diffusing across the phospholipid bilayer directly, or via aquaporins (small transmembrane proteins similar to those in facilitated diffusion and in creating ion channels). Osmosis provides the primary means by which water is transported into and out of cells. The turgor pressure of a cell is largely maintained by osmosis, across the cell membrane, between the cell interior and its relatively hypotonic environment. For the song by Girls Aloud see Biology (song) Biology studies the variety of life (clockwise from top-left) E. coli, tree fern, gazelle, Goliath beetle Biology (from Greek: βίος, bio, life; and λόγος, logos, speech lit. ... A biological membrane or biomembrane is an enclosing or separating tissue which acts as a barrier within or around a cell. ... Benzene is the simplest of the arenes, a family of organic compounds An organic compound is any member of a large class of chemical compounds whose molecules contain carbon. ... Polysaccharides (sometimes called glycans) are relatively complex carbohydrates. ... Sideview of Aquaporin 1 (AQP1) Channel Aquaporins are a class of integral membrane proteins or more commonly referred to as a class of major intrinsic proteins (MIP) that form pores in the membrane of biological cells. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell being used to describe the smallest unit of a living organism Cells in culture, stained for keratin (red) and DNA (green) The cell is the... Turgor (also called turgor pressure or osmotic pressure) is the pressure that can build in a space that is enclosed by a membrane that is permeable to a solvent of a solution such as water but not to the solutes of the soluton. ...

Contents

Basic explanation

Consider a permeable membrane, such as visking tubing, with apertures big enough to allow water (solvent) molecules, but not larger solute molecules, to pass through. When this membrane is immersed in liquid it is constantly hit by molecules of the liquid, in motion due to their thermal kinetic energy. In this respect solute and solvent molecules are indistinguishable. At a molecular scale, every time a molecule hits the membrane it has a defined likelihood of passing through. Here, there is a difference: for water molecules this probability is non-zero; for solute molecules it is zero. Visking tubing, also known as dialysis tubing, is tubing with a semi-permeable exterior, thus allowing the osmosis of small molecules, such as water, through its wall, while preventing larger molecules such as starch and proteins from passing through. ... In thermal physics, thermal energy is the energy portion of a system that increases with its temperature. ...


Suppose the membrane is in a volume of pure water. In this case, since the circumstances on both sides of the membrane are equivalent, water molecules pass in each direction at the same rate; there is no net flow of water through the membrane.


If there is a solution on one side, and pure water on the other, the membrane is still hit by molecules from both sides at the same rate. However, some of the molecules hitting the membrane from the solution side will be solute molecules, and these will not pass through the membrane. So water molecules pass through the membrane from this side at a slower rate. This will result in a net flow of water to the side with the solution. Assuming the membrane does not break, this net flow will slow and finally stop as the pressure on the solution side becomes such that the movement in each direction is equal: dynamic equilibrium. This could either be due to the water potential on both sides of the membrane being the same, or due to osmosis being inhibited by factors such as pressure potential or Osmotic pressure.


Osmosis can also be explained via the notion of entropy, from statistical mechanics. As above, suppose a permeable membrane separates equal amounts of pure solvent and a solution. Since a solution possesses more entropy than pure solvent, the second law of thermodynamics states that solvent molecules will flow into the solution until the entropy of the combined system is maximized. Notice that, as this happens, the solvent loses entropy while the solution gains entropy. Equilibrium, hence maximum entropy, is achieved when the entropy gradient becomes zero. For other uses, see: information entropy (in information theory) and entropy (disambiguation). ... Statistical mechanics is the application of probability theory, which includes mathematical tools for dealing with large populations, to the field of mechanics, which is concerned with the motion of particles or objects when subjected to a force. ... The second law of thermodynamics is an expression of the universal law of increasing entropy. ... In thermodynamics, a thermodynamic system is said to be in thermodynamic equilibrium when it is in thermal equilibrium, mechanical equilibrium, and chemical equilibrium. ...


Examples of osmosis

Effect of different solutions on blood cells
Effect of different solutions on blood cells
Plant cell under different enviroments
Plant cell under different enviroments

Osmotic pressure is the main cause of support in many plants. The osmotic entry of water raises the turgor pressure exerted against the cell wall, until it equals the osmotic pressure, creating a steady state. Image File history File links Osmotic_pressure_on_blood_cells_diagram. ... Image File history File links Osmotic_pressure_on_blood_cells_diagram. ... Image File history File links Turgor_pressure_on_plant_cells_diagram. ... Image File history File links Turgor_pressure_on_plant_cells_diagram. ... This article or section does not adequately cite its references or sources. ... Plant cells separated by transparent cell walls. ... In ionic steady state cells maintain different internal and external concentrations of various ionic species [1]. The interior of the cell is rich in carboxylic acids and cells balance this negative charge by positively charged counterions. ...


When a plant cell is placed in a hypertonic solution, the water in the cells moves to an area higher in solute concentration, and the cell shrinks and so becomes flaccid. (This means the cell has become plasmolysed - the cell membrane has completely left the cell wall due to lack of water pressure on it; the opposite of turgid.) Plasmolysis is the contraction of cells within plants due to the loss of water through osmosis. ... Look up cell membrane in Wiktionary, the free dictionary. ...


Also, osmosis is responsible for the ability of plant roots to suck up water from the soil. Since there are many fine roots, they have a large surface area, water enters the roots by osmosis.


Osmosis can also be seen very effectively when potato slices are added to a high concentration of salt solution. The water from inside the potato moves to the salt solution, causing the potato to shrink and to lose its 'turgor pressure'. The more concentrated the salt solution, the bigger the difference in size and weight of the potato slice.


In unusual environments, osmosis can be very harmful to organisms. For example, freshwater and saltwater aquarium fish placed in water of a different salinity than that they are adapted to will die quickly, and in the case of saltwater fish, rather dramatically. Another example of a harmful osmotic effect is the use of table salt to kill leeches and slugs.
For the village on the Isle of Wight, see Freshwater, Isle of Wight. ... Marine aquarium fish species are much more difficult to deal with in the aquarium than freshwater varieties. ... For other uses, see Leech (disambiguation). ... This article is about land slugs. ...


Suppose we place an animal or a plant cell in a solution of sugar or salt in water.

  1. If the medium is hypotonic — a dilute solution, with a higher water concentration than the cell — the cell will gain water through osmosis.
  2. If the medium is isotonic — a solution with exactly the same water concentration as the cell — there will be no net movement of water across the cell membrane.
  3. If the medium is hypertonic — a concentrated solution, with a lower water concentration than the cell — the cell will lose water by osmosis.[2]

Chemical gardens demonstrate the effect of osmosis in inorganic chemistry. A Chemical garden is an experiment normally done by adding solid metal saits such as copper sulfate or cobalt chloride to a solution of sodium silicate (waterglass) in water. ...


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. This article is about pressure in the physical sciences. ... For other uses, see Force (disambiguation). ... Making a saline water solution by dissolving table salt (NaCl) in water This article is about chemical solutions. ... Turgor (also called turgor pressure or osmotic pressure) is the pressure that can build in a space that is enclosed by a membrane that is permeable to a solvent of a solution such as water but not to the solutes of the soluton. ... This article or section does not adequately cite its references or sources. ... In chemistry, colligative properties are factors that determine how the properties of a bulk liquid solution change depending on the concentration of the solute in the bulk solution. ...


Increasing the pressure increases the chemical potential of the system in proportion to the molar volume (δμ = δPV). Therefore, osmosis stops when the increase in potential due to pressure equals the potential decrease from Equation 1, i.e.: In chemistry, the molar volume of a substance is the ratio of the volume of a sample of that substance to the amount of substance (usually in mole) in the sample. ...


delta PV = -RT ln(1-x_2)qquad (2)


Where δP is the osmotic pressure and V is the molar volume of the solvent.


delta P = RTx_2/V qquad (3)


Reverse osmosis

Main article: Reverse osmosis

Reverse osmosis is a separation process that uses pressure to force a solvent through a membrane that retains the solute on one side and allows the pure solvent to pass to the other side. ...

Forward osmosis

Main article: Forward osmosis

Osmosis may be used directly to achieve separation of water from a "feed" solution containing unwanted solutes. A "draw" solution of higher osmotic pressure than the feed solution is used to induce a net flow of water through a semi-permeable membrane, such that the feed solution becomes concentrated as the draw solution becomes dilute. The diluted draw solution may then be used directly (as with an ingestible solute like glucose), or sent to a secondary separation process for the removal of the draw solute. This secondary separation can be more efficient than a reverse osmosis process would be alone, depending on the draw solute used and the feedwater treated. Forward osmosis is an area of ongoing research, focusing on applications in desalination, water purification, water treatment, food processing, etc. Forward Osmosis is an osmotic process that, like reverse osmosis, uses a semi-permeable membrane to effect separation of water from dissolved solutes. ... Forward Osmosis is an osmotic process that, like reverse osmosis, uses a semi-permeable membrane to effect separation of water from dissolved solutes. ... Shevchenko BN350 desalination unit situated on the shore of the Caspian Sea. ... Control room and schematics of the water purification plant to Bret lake. ... A water treatment plant in northern Portugal. ... Food processing is the set of methods and techniques used to transform raw ingredients into food for consumption by humans or animals. ...


See also

Wikibooks
Wikibooks' [[wikibooks:|]] has more about this subject:
School science/Osmosis demonstration

Image File history File links Wikibooks-logo-en. ... diffusion (disambiguation). ... Plant cell under different enviroments Before plasmolysis. ... This does not cite any references or sources. ...

References

  1. ^ Osmosis
  2. ^ http://www.cbse.nic.in

External links

  • Osmosis simulation in Java
Look up Osmosis in
Wiktionary, the free dictionary.

  Results from FactBites:
 
Osmosis - Wikipedia, the free encyclopedia (1128 words)
Osmosis is the diffusion of a liquid (most often assumed to be water, but it can be any liquid solvent) through a semipermeable membrane from a region of low solvent potential to a region of high solvent potential.
Osmosis is an important topic in biology because it provides the primary means by which water is transported into and out of cells.
The osmosis process can be driven in reverse with solvent moving from a region of high solute concentration to a region of low solute concentration by applying a pressure in excess of the osmotic pressure.
Osmosis Jones - Wikipedia, the free encyclopedia (1177 words)
Osmosis Jones (2001) is a part animated, part live action film whose title character is Osmosis Jones, an anthropomorphic white blood cell.
Eventually, Osmosis and Drix confront Thrax in one of Frank's zits.
Osmosis' prediction rings true as Thrax was able to survive the explosion and decides to launch a one-man assault on Frank's brain (there were two other germs with him but he murdered them as soon as they suggested going into hiding).
  More results at FactBites »

 
 

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