Osmosis About Watch and Favorite Watch Watching this resources will notify you when proposed changes or new versions are created so you can keep track of improvements that have been made. Favorite Favoriting this resource allows you to save it in the “My Resources” tab of your account. There, you can easily access this resource later when you’re ready to customize it or assign it to your students. Osmosis Osmosis is the movement of water across a membrane from an area of low solute concentration to an area of high solute concentration. Learning Objective Describe the process of osmosis and explain how concentration gradient affects osmosis Key Points Osmosis occurs according to the concentration gradient of water across the membrane, which is inversely proportional to the concentration of solutes . Osmosis occurs until the concentration gradient of water goes to zero or until the hydrostatic pressure of the water balances the osmotic pressure . Osmosis occurs when there is a concentration gradient of a solute within a solution, but the membrane does not allow diffusion of the solute.

Terms Full Text Osmosis and Semipermeable Membranes Osmosis is the movement of water through a semipermeable membrane according to the concentration gradient of water across the membrane, which is inversely proportional to the concentration of solutes. Semipermeable membranes, also termed selectively permeable membranes or partially permeable membranes, allow certain molecules or ions to pass through by diffusion. While diffusion transports materials across membranes and within cells , osmosis transports only water across a membrane. The semipermeable membrane limits the diffusion of solutes in the water. Not surprisingly, the aquaporin proteins that facilitate water movement play a large role in osmosis, most prominently in red blood cells and the membranes of kidney tubules. Mechanism of Osmosis Osmosis is a special case of diffusion. Water, like other substances, moves from an area of high concentration to one of low concentration. An obvious question is what makes water move at all? Imagine a beaker with a semipermeable membrane separating the two sides or halves.

On both sides of the membrane the water level is the same, but there are different concentrations of a dissolved substance, or solute, that cannot cross the membrane (otherwise the concentrations on each side would be balanced by the solute crossing the membrane). If the volume of the solution on both sides of the membrane is the same but the concentrations of solute are different, then there are different amounts of water, the solvent, on either side of the membrane. If there is more solute in one area, then there is less water; if there is less solute in one area, then there must be more water. To illustrate this, imagine two full glasses of water. One has a single teaspoon of sugar in it, whereas the second one contains one-quarter cup of sugar. If the total volume of the solutions in both cups is the same, which cup contains more water? Because the large amount of sugar in the second cup takes up much more space than the teaspoon of sugar in the first cup, the first cup has more water in it. Osmosis Glossary Osmosis Large quantities of water molecules constantly move across cell membranes by simple diffusion, often facilitated by movement through membrane proteins, including aquaporins .

In general, net movement of water into or out of cells is negligible. For example, it has been estimated that an amount of water equivalent to roughly 100 times the volume of the cell diffuses across the red blood cell membrane every second; the cell doesn't lose or gain water because equal amounts go in and out. There are, however, many cases in which net flow of water occurs across cell membranes and sheets of cells. An example of great importance to you is the secretion of and absorption of water in your small intestine . In such situations, water still moves across membranes by simple diffusion, but the process is important enough to warrant a distinct name - osmosis. Osmosis is the net movement of water across a selectively permeable membrane driven by a difference in solute concentrations on the two sides of the membrane. A selectively permiable membrane is one that allows unrestricted passage of water, but not solute molecules or ions. Different concentrations of solute molecules leads to different concentrations of free water molecules on either side of the membrane. On the side of the membrane with higher free water concentration (i.e. a lower concentration of solute), more water molecules will strike the pores in the membrane in a give interval of time.

More strikes equates to more molecules passing through the pores, which in turn results in net diffusion of water from the compartment with high concentration of free water to that with low concentration of free water. The key to remember about osmosis is that water flows from the solution with the lower solute concentration into the solution with higher solute concentration. This means that water flows in response to differences in molarity across a membrane. The size of the solute particles does not influence osmosis. Equilibrium is reached once sufficient water has moved to equalize the solute concentration on both sides of the membrane, and at that point, net flow of water ceases. Here is a simple example to illustrate these principles: Two containers of equal volume are separated by a membrane that allows free passage of water, but totally restricts passage of solute molecules. Solution A has 3 molecules of the protein albumin (molecular weight 66,000) and Solution B contains 15 molecules of glucose (molecular weight 180). Into which compartment will water flow, or will there be no net movement of water? [ answer ] Additional examples of how to determine which direction water will flow in different circumstances are provided.

When thinking about osmosis, we are always comparing solute concentrations between two solutions, and some standard terminology is commonly used to describe these differences: Isotonic: The solutions being compared have equal concentration of solutes. Hypertonic: The solution with the higher concentration of solutes. Hypotonic: The solution with the lower concentration of solutes. In the examples above, Solutions A and B are isotonic (with each other), Solutions A and B are both hypertonic compared to Solution C, and Solution C is hypotonic relative to Solutions A and B. Diffusion of water across a membrane generates a pressure called osmotic pressure. If the pressure in the compartment into which water is flowing is raised to the equivalent of the osmotic pressure, movement of water will stop. This pressure is often called hydrostatic ('water-stopping') pressure. The term osmolarity is used to describe the number of solute particles in a volume of fluid. Osmoles are used to describe the concentration in terms of number of particles - a 1 osmolar solution contains 1 mole of osmotically-active particles (molecules and ions) per liter.

You can investigate these principles further using an osmosis and hydrostatic pressure simulator . The classic demonstration of osmosis and osmotic pressure is to immerse red blood cells in solutions of varying osmolarity and watch what happens. Blood serum is isotonic with respect to the cytoplasm, and red cells in that solution assume the shape of a biconcave disk. To prepare the images shown below, red cells from your intrepid author were suspended in three types of solutions: Isotonic - the cells were diluted in serum: Note the beautiful biconcave shape of the cells as they circulate in blood. Hypotonic - the cells in serum were diluted in water: At 200 milliosmols (mOs), the cells are visibly swollen and have lost their biconcave shape, and at 100 mOs, most have swollen so much that they have ruptured, leaving what are called red blood cell ghosts. In a hypotonic solution, water rushes into cells.

Hypertonic - A concentrated solution of NaCl was mixed with the cells and serum to increase osmolarity: At 400 mOs and especially at 500 mOs, water has flowed out of the cells, causing them to collapse and assume the spiky appearance you see. Predict what would happen if you mixed sufficient water with the 500 mOs sample shown above to reduce its osmolarity to about 300 mOs. Advanced and Supplemental Topics Movement | S-cool, the revision website S-cool, the revision website Submitted by Anonymous on Fri, 11/13/2015 - 10:06 It is important that the cell is supplied with all the substances it needs (e.g. oxygen) and that waste substances (e.g. carbon dioxide), or substances for export, leave the cell. There are various processes by which this can happen... Diffusion This is the process that is used in oxygen entering a cell, and carbon dioxide leaving. These molecules will move from where they are at a high concentration to where they are at a lower concentration. i.e. they diffuse down a concentration gradient.

The blood system in humans continually brings more oxygen to the cell and takes carbon dioxide away. This maintains a high concentration gradient. Since the movement is always down the concentration gradient, it requires no energy. The small molecules pass from one side of the membrane to the other by moving between the lipid molecules. Fick's law is used to measure the rate of diffusion. It states that: (The symbol α means 'proportional to') The larger the area and difference in concentration and the thinner the surface, the quicker the rate. So, for example, in the lung the surface area is made very large by the presence of many alveoli. The difference in concentration is maintained by breathing, which brings in air with a high oxygen concentration and removes the air with a high carbon dioxide concentration and by a good blood supply. The capillaries surrounding the alveoli take away the oxygenated blood and replace it with blood with a high carbon dioxide concentration. The walls of the alveoli are only one cell thick, so the surface across which diffusion occurs is thin and the rate is high. In plants, a good example would be root hair cells.

They have a very large surface area due to the drawing out of the cytoplasm to produce a very fine root hair. Water continues to enter the root by osmosis because there is a high concentration of mineral salts in the cells and the water is moved up the plant by the xylem. Water only has to penetrate one cell in order to enter the plant and so again the rate of diffusion is high. Osmosis This is a special case of diffusion in which we are concerned only with the movement of water. If two solutions are separated by a semi-permeable membrane, which only allows certain sized molecules through (as in a plasma membrane), there will be a net (overall) movement of the water molecules, from the less concentrated solution (the one with more water molecules), to the solution which is more concentrated (has more solute molecules). This is because as in ordinary diffusion the molecules move to even-out any difference in concentration. However, because of the semi-permeable membrane, which does not allow the larger solute molecules to cross, only the water molecules can move. The water molecules will continue to cross the semi-permeable membrane until an equilibrium is reached, where the two solutions are of equal concentration.

Water potential This is a measure of the tendency of water molecules to move from one place to another. The symbol used for water potential is the Greek letter psi, Ψ Water always moves from a region of higher water potential to one of lower water potential, or down the concentration gradient. So we can define osmosis as the movement of water molecules from a region of higher water potential to a region of lower water potential through a semi-permeable membrane. Solute potential and pressure potential The water potential of a cell is dependent upon the combination of its solute and pressure potentials. The water potential of pure water is zero and since adding solutes lowers water potential, they make the water potential less than zero, i.e. negative. The more solute, the more negative the water potential becomes. The amount that the solute molecules lower the water potential is called the solute potential. It always has a negative value and is given the symbol, Ψs Pressure also has a role to play in determining water potential. The greater the pressure inside a cell, the greater the tendency will be for water to leave it. This contribution to water potential is called the pressure potential.

It always has a positive value because it increase water potential and is given the symbol Ψp Osmosis in animal and plant cells If the water potential surrounding an animal cell is higher than that of the cell, it will gain water, swell and burst. If the surrounding solution's water potential is lower than that of the cell, it will lose water and shrivel up. This is why it is so important to maintain a constant water potential inside the bodies of animals. In animal cells: Or: Ψ = Ψs Pressure potential is important in plant cells because they are surrounded by a cell wall which, is strong and rigid. When water enters a plant cell, its volume increases and the living part of the cell presses on the cell wall. The cell wall gives very little and so pressure starts to build up inside the cell. This has the tendency to stop more water entering the cell and also stops the cell from bursting. When a plant cell is fully inflated with water, it is called turgid.

So in plant cells the equation used to calculate the water potential of a cell is therefore: Water potential = Solute potential + Pressure potential Or: Ψ = Ψs + Ψp If a plant cell is placed in a solution with a lower water potential, it will loose water. The living part of the cell or protoplast will shrink and pull away from the cell wall. At this point the pressure potential is zero and so the water potential of the cell is equal to its solute potential. This process is called plasmolysis and the cell is said to be plasmolysed. The point at which the protoplast is just about to pull away from the cell wall is called incipient plasmolysis. BBC Bitesize - GCSE Biology - Movement across cell membranes - Revision 3 Living organisms Movement across cell membranes Substances can move into and out of cells through the cell membrane. The three main types of movement are diffusion, osmosis and active transport. Revise 3 of 7 Osmosis Osmosis is the diffusion of water molecules, from a region of higher concentration to a region of lower concentration, through a partially permeable membrane.

A dilute solution contains a high concentration of water molecules, while a concentrated solution contains a low concentration of water molecules. Partially permeable membranes are also called selectively permeable membranes or semi-permeable membranes. They let some substances pass through them, but not others. The slideshow shows an example of osmosis: 2 In the slideshow, eventually the level on the more concentrated side of the membrane rises, while the one on the less concentrated side falls. When the concentration is the same on both sides of the membrane, the movement of water molecules will be the same in both directions. At this point, the net exchange of water is zero and there is no further change in the liquid levels. < alveoli Tiny air sacs in the lungs, where gas is exchanged during breathing. cellulose A carbohydrate. It forms the cell wall in plant cells. concentration gradient The difference in the concentration of a chemical across a membrane. cytoplasm The living substance inside a cell (not including the nucleus). diffusion The movement of particles (molecules or ions) from an area of higher concentration to an area of lower concentration. glucose A simple sugar made by the body from food, which is used by cells to make energy in respiration.

isotonic Two solutions at the same concentration are described as isotonic. mass The amount of matter an object contains. Mass is measured in 'kg'. osmosis The movement of water molecules across a partially-permeable membrane from a region of low solute concentration to a region of high solute concentration. partially permeable Also called semi-permeable. A partially permeable membrane allows water and other small molecules to pass through but not larger molecules such as starch. respiration Chemical change that takes place inside living cells, which uses glucose and oxygen to produce the energy organisms need to live. Carbon dioxide is a by-product of respiration. solute The dissolved substance in a solution. solvent The liquid in which the solute dissolves to form a solution. starch A type of carbohydrate. Plants can turn the glucose produced in photosynthesis into starch for storage, and turn it back into glucose when it is needed for respiration. sucrose A disaccharide made from glucose and fructose, it is used as table sugar. turgid Enlarged and swollen with water. Having turgor. villi Finger-like projections in the small intestine that provide a large surface area for the absorption of food.

Diffusion and Osmosis - Difference and Comparison | Diffen Diffusion and Osmosis Diffen › Science › Biology › Cellular Biology Osmosis is the result of diffusion across a semipermeable membrane. If two solutions of different concentration are separated by a semipermeable membrane, then the solvent will tend to diffuse across the membrane from the less concentrated to the more concentrated solution. This process is called osmosis. At the cellular level, both processes are types of passive transport . Semipermeable membranes are very thin layers of material that allow small molecules, like oxygen, water, carbon dioxide, ammonia, glucose, amino-acids, etc., to pass through. However, they do not allow larger molecules, like sucrose, protein, etc., to pass through. Comparison chart Diffusion versus Osmosis comparison chart Diffusion Osmosis What is it? Diffusion is a spontaneous movement of particles from an area of high concentration to an area of low concentration. (ex. tea flavoring moving from an area of high to low concentration in hot water.) Osmosis is the spontaneous net movement of water across a semipermeable membrane from a region of low solute concentration to a more concentrated solution, up a concentration gradient.

This equalizes concentrations on both sides of the membrane. Process Diffusion mainly occurs in gaseous state or within gas molecules and liquid molecules.(e.g. The molecules of 2 gases are in constant motion and if the membrane separating them is removed the gases will mix because of random velocities.) It occurs when the medium surrounding the cell has a higher water concentration than the cell. The cell gains water along with important molecules and particles for growth. It also occurs when water and particles move from one cell to another. Importance To create energy ; Helps in exchange of gases during respiration, photosynthesis , and transpiration. In animals, osmosis influences the distribution of nutrients and the release of metabolic waste products. In plants, osmosis is partially responsible for the absorption of soil water and for the elevation of the liquid to the leaves of the plant. Concentration Gradient Goes from a high concentration gradient to a low concentration gradient Moves down concentration gradient Doesn’t need water for movement Needs water for movement Perfume or Air Freshener where the gas molecules diffuse into the air spreading the aroma. Movement of water into root hair cells. Contents: Diffusion and Osmosis 4 References Process of Osmosis vs. Diffusion The process of diffusion.

Some particles (red) are dissolved in a glass of water. Initially, the particles are all near one corner of the glass. When the particles all randomly move around ("diffuse") in the water, they eventually become distributed randomly and uniformly. Diffusion occurs when the spontaneous net movement of particles or molecules spreads them from an area of high concentration to an area of low concentration through a semipermeable membrane. It is simply the statistical outcome of random motion. As time progresses, the differential gradient of concentrations between high and low will drop (become increasingly shallow) until the concentrations are equalized. Diffusion increases entropy (randomness), decreasing Gibbs free energy , and therefore is a clear example of thermodynamics. Diffusion operates within the boundaries of the Second Law of Thermodynamics because it demonstrates nature's tendency to "wind down", to seek a state of less concentrated energy, as evidenced by increasing entropy. Osmosis is the process of diffusion of water across a semipermeable membrane. Water molecules are free to pass across the cell membrane in both directions, either in or out, and thus osmosis regulates hydration, the influx of nutrients and the outflow of wastes, among other processes.

Osmosis in a plant cell For example, if the medium surrounding the plant or animal cell has a higher water concentration than the cell, then the cell will gain water by osmosis. The overall result is that water enters the cell and the cell is likely to hydrate and swell. If the medium has lower concentration of water than the cell, it will lose water by osmosis as this time more water leaves the cell than enters it. Therefore the cell will shrink. If the water concentration in the medium is exactly the same then the cell will stay the same size while that concentration balance remains. In every situation, the movement of solvent is from the less-concentrated ( hypotonic ) to the more-concentrated ( hypertonic ) solution, which tends to reduce the difference in concentration (equalization). Differences in Function While osmosis influences the distribution of nutrients and the release of metabolic waste products in animals; in plants, osmosis is partially responsible for the absorption of soil water and for the elevation of the liquid to the leaves of the plant.

Diffusion can occur through a cell membrane, and the membrane allows small molecules like water (H2O), oxygen (O2), carbon dioxide (CO2), and others to pass through easily. Hence while osmosis helps the plants in absorbing water and other liquids, diffusion helps other molecules to pass through and hence both facilitate the photosynthesis process. Both processes help plants to create energy and other important nutrients. Different Types of Osmosis and Diffusion Osmotic effect of different solutions on blood cells The two types of Osmosis are: Reverse Osmosis: The osmotic pressure defines at what point a differential gradient between high and low solute triggers osmosis. In reverse osmosis, increased volumetric or atmospheric pressure will "push" the higher solute particles past the membrane, overcoming the gap that may exist when the osmotic pressure won't allow diffusion through the membrane. This process is often used to filter water of impurities when their concentrations are too low for regular osmosis, but cleaner water is still needed, as in desalination and pharmaceutical operations.

Forward Osmosis: Unlike reverse osmosis, which goes from high-to-low concentrations, forward osmosis forces low solute particles to move to a higher solute — in essence, the opposite of the normal osmotic process. Whereas reverse osmosis "pushes" particles, forward osmosis "draws" them in, resulting in cleaner water. The types of diffusion are: Surface diffusion: Seen after dropping powdery substances on a liquid's surface. Brownian motion: The random motion observed under a microscope as particles skip, slip, and dart within a liquid. Collective diffusion: The diffusion of a large number of particles within a liquid that remain intact or interacting with other particles. Osmosis: The diffusion of water through a cell membrane. Effusion: Happens as a gas disperses through small holes. Electron diffusion: The movement of electrons resulting in electric current. Facilitated diffusion: Spontaneous passive transport of ions or molecules across a cell membrane (different because it happens outside the active phase of osmosis or intracellular diffusion). Gaseous diffusion: Used mainly with uranium hexafluoride to produce enriched uranium for nuclear reactors and weapons .

Knudsen diffusion: A variable measure of particle interactivity within a membrane pore, related to the particle's size and the length and diameter of the pore. Momentum diffusion: The spread of momentum between particles mainly in liquids, influenced by the liquid's viscosity (higher viscosity = higher momentum diffusion). Photon Diffusion: Movement of photons within a material, then scattering as they bounce off of different densities within. Used in medical tests as diffuse optical imaging . Reverse Diffusion: Similar to forward osmosis, with low concentration moving to high, but refers to a separation of particles, not just water. Self-diffusion: A coefficient measuring how much diffusion a type of particle will have when the chemical gradient is zero (neutral or balanced). References OSMOSIS and DIFFUSION back to Help_centre main . This page maintained by Dr KNI Bell (questions&suggestions welcome) No, OSMOSIS was not an Egyptian pharoah. useful web sites (you have seen the lecture page, right? (Dr Bell's [& others'] lecture page for Unit 07 plasma membrane, osmosis)) ~iemerson , follow link "Biology 1001 ...

1997" then choose "Diffusion Osmosis Tutorial". Tutorial has self-tests and is tailored to the expectations of the course. . Follow the links on the right hand side to the topic sections. Includes very nice graphical illustrations that get down to the "meat" of what goes on. STUDY ADVICE AGAIN: [1] start with definitions (yucky-coloured glossary pages in your text, other glossaries, the dictionary), THEN [2] use the INDEX and go to detailed explanations. [3] It's often useful to see the same thing in two different texts. [4] Find joy in whatever you do. To get you started, here are some of our yucky-coloured definitions (mostly from Dr. Whittick's Glossary ). diffusion: the movement of a substance from an area of high concentration to an area of lower concentration until an equilibrium is reached. OSMOLARITY: an absolute measure of the concentration of solute in a solution.

In contrast, the "-tonic" terms are relative, always in the context of comparison of 2 (not 1, not 3) solutions; if considering two solutions, A of low and B of high osmolarity, A will be hypotonic to B. (The term "osmolarity" is usually deferred until 1002, but in a way it's a much simpler concept and therefore some students will find TONICITY easier to deal with if they learn osmolarity first.) hypertonic: concerning osmosis, a term used to compare one solution with another, a hypertonic solution has a higher concentration of solutes, when separated by a membrane that is permeable to the solvent and impermeable to the solute. In this instance the solvent will flow from the region of lower solute concentration (hypotonic) to the region of higher concentration (hypertonic) by the process of osmosis. e.g. most fresh water protists are hypertonic when compared with their environment. hypotonic: (see hypertonic for a detailed description) a solution that has a lower concentration of solutes than a hypertonic one.

isotonic: (see hypertonic or hypotonic) when two solutions separated by a membrane permeable to the solvent but not the solutes are of equal concentration this results in no net movement of solvent across the membrane. osmosis: the phenomenon whereby water flows across a selectively permeable membrane from a hypotonic environment to a hypertonic environment. selectively permeable: applies to membranes which allow one substance to pass, but impede another. (You need to establish what the membrane is and isn't permeable to, recognising that you are interested in the difference between "pass through easily" and "hardly ever get past".) Usually, biological membranes (and things that mimic their performance) are permeable to water but not permeable to (or much less permeable than) solutes (e.g. sugars, ions). osmoregulation: the ability of a cell or an organism to regulate its internal concentration of water or salts in order to maintain it self in a an specific environment e.g. the contractile vacuole of Euglena actively expels water from the cell which enters as a result of the cell being hypertonic in comparison with the fresh water environment.

...some terms relating to plant cells plasmolysed: when a living cell with a cell wall is placed in a hypertonic solution it loses water by osmosis, if sufficient water is lost the cell membrane is pulled away from the cell wall and the cell is said to be plasmolysed. plasmolysis: the act of becoming plasmolysed, see above. turgid: means firm, the opposite of flaccid, cells with wall become firm as a result of the uptake of water by osmosis, turgor: (pressure) the force exerted on a cell wall by a cell membrane as a result of osmotic uptake of water. ... some terms relating to transport of other substances active transport: the movement of a substance across a cell membrane against its concentration gradient, which requires energy from the cell passive transport: a form of transport which requires no energy from the organism, i.e. diffusion of a substance from an area of high concentration to one of a lower one. OSMOSIS IS IMPORTANT BECAUSE IT DETERMINES WHERE WATER GOES, HOW IT CAN BE CONTROLLED WATER is an essential substance in life and it must be managed.

This management has to rely on the laws of physics. A key observation that is often overlooked is: water is NEVER actively transported. There are no enzymes to actively transport water, only enzymes to actively transport solutes that affect osmosis. Organisms manage water by managing OSMOSIS. (Downhome example no. 1) Moving water? It's kind of like moving a pig. Ever try to move a pig? Pigs are not only stubborn and suspicious, they are large and very strong. I had a friend Jerry who was farming out in St. George's Bay. Lovely area. One day, Jerry had finished building a beautiful new pigpen -- elevated floor, good roof, shade area for those hot days, etc., everything a pig could want, even an ocean view -- for his pig, and cheerfully walked over to the pig with a piece of rope to lead the pig happily to its beautiful new home. Dogs know about leashes, but pigs -- as I said, large, strong, stubborn.

So Jerry pulled and pulled on this rope, pulled as hard as he could, and the pig pulled the other way, or maybe it just stood still pondering the contribution of cometary debris to the chemical composition of the atmosphere of Io, it's hard to tell with pigs. So, after Jerry skidding his feet on the mud for a while, all that happened was he got tired and upset. Offended perhaps. The pig wasn't upset, it simply wasn't interested in going anywhere it hadn't seen yet, certainly not at the end of a rope. No sale, you might say. Jerry gave up and went to get the tractor, by golly he was going to just haul that pig over there and a diesel International tractor with 60-inch wheels and a differential lock was just the item to show that pig who was boss. Off he went. Jerry was more partial to tractors anyhow -- easier to understand. But Jerry's daughter Elizabeth liked animals, and took a jug of pig food, and held it out for the pig and spread a little on the ground. The pig followed the trail all the way to the new pigpen. Only took a minute or two.

ï¿½ï¿½Food speaks the pig's language; rope doesn't. Jerry came roaring back on the tractor, and the move had been made. -- So, just as the pig couldn't be pulled by a rope, water can't be actively transported. Just as the pig would move spontaneously to food, water can be induced to flow in the direction of solute gradients. And many solutes can be actively transported, and cells do this all the time. (My colleagues may want to shoot me for that, but just as a building requires scaffolding during its construction, conceptualisation can benefit from analogies. If the analogy doesn't work for you, don't worry, just move on.) We leave the barnyard and move on to the technical terms. Coffeecup analogies (remember, coffee is mostly water): OSMOLARITY is a number referring to the number of moles of solute in a solution (we usually get to this in Biology 1002, but in fact it is a simple concept and for many people it's a better starting point). ----For a cup of coffee with no solutes, osmolarity = 0. Add solutes, osmolarity goes up.

If you take one spoon of sugar and your friend takes two spoons, the osmolarity of your friend's coffee is higher. And therefore, your coffee would be hypotonic to your friend's, or your friend's would be hypertonic to yours. (That's not so hard.) ----Though your coffee would be hypotonic to your friend's, your coffee would be hypertonic to the no-sugar cup. That's not so hard either: the "-tonic" terms are always relative (describing one thing relative to one other), not absolute. So if someone asks you "is this hypotonic" you can only ask "compared to what?" Only osmolarity is absolute: comparing any solution A to any solution B with a greater osmolarity, A will be hypotonic to B and B hypertonic to A, and comparing A to any solution with a lesser osmolarity A will be hypertonic. ------- ----Finally, what will water do ... i.e. how can you use these concepts to understand osmosis? ----Every molecule in a liquid or in solution is mobile, and it can move in any direction. However, the rate of movement is affected by the presence of other molecules.

DIFFUSION is the net movement, the change in distribution over time. E.g., in the case of sugar put into water, supposing molecular motion of water results in, say, 335 movements toward the sugar (where the solute concentration is higher) and, say, 319 movements away, then the net movement is 16 toward and that has the effect of reducing the solute concentration there; the sugar does the same; eventually this process would eliminate all gradients until the sugar molecules and water molecules were uniformly distributed. The bias in movement of molecules is caused by the bias in solute concentration (no bias would mean no net movement). ----Next, suppose you put two different solutions in a coffee mug (as we just did) but with a divider that was permeable to water but not to sugar (a selectively permeable membrane), and you put sweet coffee on the right and much sweeter coffee on the left. (Is the sweet coffee hyp[O or ER]tonic to the much sweeter coffee?

hypOtonic<--drag mouse to see answer) ---- Now you've sorted out which is hypotonic to which, can you identify the direction of OSMOSIS, the direction of net movement of water across the selectively permeable membrane? (Osmosis will be in the direction of the sweeter coffee, i.e. net water movement will be from the solution with less sugar (hypotonic, more water) to the solution with more sugar (hypertonic, less water).<--drag mouse to see answer) Osmosis tends to equalise solute concentrations, because net movement of water is from lower osmolarity to higher osmolarity. If you'd like another example: think about adding sugar to a glass of water: 2. throw in the sugar cube and don't stir. Imagine what happens: does the sugar remain in a cube? No, you can't lift the cube out again. 3. throw in the sugar, stir well, and wait 2 days. Does the sugar come out of solution and form grains again? (No, it stays dissolved). What does this tell us? Unstirred, the water and the sugar molecules spontaneously diffused to form a syrup.

The water concentration was initially zero (or very low) in the sugar grains, and the sugar concentration was initially zero (low) in the coffee. Water moved down its concentration gradient, and sugar moved down its concentration gradient. Note that this movement of molecules would continue until there was no gradient, i.e. until the coffee is uniformly sweet and there are no undissolved (grains of) sugar left. In this case diffusion of BOTH the water and the solute (sugar in this case) contributed to elimination of all concentration gradients. any area that has a higher concentration of solute (sugar) can be called hypertonic compared to any area that has a lower concentration of solute (hypotonic), and ... ... if these areas are separated by a selectively permeable membrane that prevents the movement of solutes, the water alone will cross the membrane and the volumes on each side of the membrane will change.

Pressure can also influence the balance of water movement across SPM: If the volumes are constrained, as in a plant cell that has a cell wall, the pressure inside the cell (if that is hypertonic compared to its environment) will rise, and as it rises the rate of diffusion out of the cell will rise until it matches the diffusion into the cell. At that point, the pressure in the cell equals (balances) the osmotic pressure generated by the solute differences. If the cell wall is not strong enough, the cell ruptures before this point is reached. That is why protozoan ectoparasites of fish can be fought by rapid changes from seawater to fresh and vice versa. Downhome example no.2: When you salt fish you use salt or a brine to 'draw' water out of the fish; the brine is hypERtonic to the fish, and the fish is hypOtonic to the brine, so the water in the fish diffuses toward the brine faster than the water in the brine diffuses toward the fish -- net movement is out of the fish. Cell survival depends on balancing water uptake and loss .

Cells can burst if they take on too much water, or collapse if they lose too much. Downhome example again: you salt fish to preserve it, by reducing the water content to a point where the bacteria that would spoil it cannot live. Now think about animal cells and plant cells in a hypotonic environment (take an extreme hypotonic environment, like distilled water). Both will take on water because osmosis will be in the direction of higher osmolarity. Generally, the plant cell will take on water until the pressure inside the cell causes a balancing of the flux of water into and out of the cell. The animal cell will take on water until it ruptures. And finally, it's good to know what you don't know, so here's something for you to find out. If the selective permeability of a membrane is based mostly on size, and solutes like Na+ and CL- are smaller than H2O, how can you have a membrane that allows water to pass but not solutes?

From KNIB&others' html lecture material, to put Osmosis into the general context of transport HOW MOLECULES GET IN AND OUT OF CELLS: (obviously, if molecules can't get in and out of cells, then cells can't obtain nutrients or release wastes, and so they die. From the cell's point of view this is a serious matter. You are made of cells, so this matters to you too.) Important words: DIFFUSION, ACTIVE TRANSPORT, PASSIVE TRANSPORT, OSMOLARITY & OSMOSIS (always relates to water movement & solute, solvent), CELL MEMBRANE, PERMEABILITY, ... A CELL MEMBRANE IS SELECTIVELY PERMEABLE (some molecules cross more easily than others). The selective permeability of a membrane depends on: Permeability of the phospholipid bilayer itself (p 136 b) Transport proteins that bridge the phospholipid bilayer (p 136 b) properties of molecules: size, polarity, charge SOME MOLECULES CROSS EASILY AND SPONTANEOUSLY.

These tend to diffuse until concentrations are equal: Nonpolar (hydrophobic) molecules dissolve in the membrane and cross it with ease (e.g., hydrocarbons, 02, C02). Small, polar uncharged molecules (e.g., H20, ethanol) rapidly pass through the plasma membrane. SOME MOLECULES DO NOT CROSS EASILY, HAVE TO BE HELPED ACROSS: Larger, polar uncharged molecules (e.g., glucose) will not easily pass through the phospholipid bilayer All ions, even small ones (e.g., Na+, H+) are hydrophilic and therefore have difficulty penetrating the hydrophobic layer Transport proteins: TO HELP SOME MOLECULES ACROSS. Transport proteins allow a way for hydrophilic substances to avoid (bypass) the hydrophobic core of the bilayer. Transport proteins thus make biological membranes permeable to specific ions and certain polar molecules of moderate size What are transport proteins? Integral membrane proteins that transport specific molecules or ions across biological membranes (see Campbell, Figure 8.8a). Often anchored to cytoskeleton. Often controlled. How do transport proteins work?

Some provide a hydrophilic tunnel through the membrane (passive transport, no energy cost). Some bind to a substance and physically move it across the membrane (active transport, costs ATP) Generally specific for the substance they translocate. Passive transport is diffusion across a membrane ( Campbell Fig.8.9 ) DIFFUSION = The spreading out of a substance as a result of the movements of individual molecules -- this implies a net movement of a substance down its concentration gradient (Campbell), until there is no gradient left. Or (Whittick) the net movement of a substance from an area of high concentration to an area of lower concentration until an equilibrium is attained. If you like, you can think of it as the destruction of a gradient by equalisation of the values all along it. This occurs molecule by molecule. Results from random molecular motion, even though the net movement may be biased down the gradient Diffusion continues until a dynamic equilibrium is reached. At equilibrium the molecules continue to move, but there is no net directional movement. Diffusion does not entail a cost to the cell, except where it has to be countered ANALOGY for 'gradient': pour honey onto a plate.

As you add it, there is more honey where you pour it; the difference between honey levels at any two places is the gradient; if two places are the same there is no gradient; over time the honey flows down whatever gradients they are, until all gradients have become zero. Then take OUT a spoonful of honey: this establishes a new gradient, etc. Concentration gradient = increase or decrease (in concentration) over distance Net directional movement = Overall movement away from the center of concentration, which results from random molecular movement in all directions. A molecule has a higher probability of moving from a high concentration to a low concentration than vice versa. In the absence of other forces or constraints (e.g., pressure) a substance will diffuse from where it is more concentrated to where it is less concentrated. A substance diffuses down its own concentration gradient. It is not affected by the gradients of other substances in the same place. Much of the traffic across cell membranes occurs by diffusion and is thus a form of passive transport.

"PASSIVE TRANSPORT is Diffusion of a substance across a [biological] membrane" (Campbell p 137a) Spontaneous process which is a function of a concentration gradient when a substance is more concentrated on one side of the membrane. does not require cell to expend energy. Rate of diffusion is regulated by the permeability of the membrane, so some molecules diffuse more freely than others. Water diffuses freely across most cell membranes. " Osmosis is the passive transport of water" (Campbell p 137d). Important words hypertonic, hypotonic, isotonic: HypERtonic solution = solution with a greater solute concentration than that inside a cell. It will 'draw' water out of a cell. HypOtonic solution = solution with a lower solute concentration than that inside a cell. Cell will tend to 'draw' water from the solution. ISOtonic solution = A solution with an equal solute concentration compared to that inside a cell. -->!! these words always refer to a comparison !!<-- i.e.

if you have two solutions that are different, the one with the lower solute concentration is hypOtonic to the other, and the one with the higher solute concentration is hypERtonic to the other. (Greek hypo- = under, hyper-=over. Hence hypodermic needle ... a hypERdermic needle would be one that never gets under your skin. Gk. 'iso' = 'same'.) Osmosis = (see Campbell, Fig.8.10 ) Diffusion of water across a selectively permeable membrane. Water diffuses down its concentration gradient, i.e. from the hypOtonic zone to the hypERtonic zone. Downhome example: When you salt fish you use salt or a brine to 'draw' water out of the fish; the brine is hypERtonic to the fish, and the fish is hypOtonic to the brine, so the water in the fish diffuses toward the brine faster than the water in the brine diffuses toward the fish -- net movement is out of the fish.

Example: If two solutions of different concentrations are separated by a selectively permeable membrane that is permeable to water but not to solute, water will diffuse from the hypotonic solution to the hypertonic solution. The direction of osmosis is determined by the difference in total solute concentration. If two isotonic solutions are separated by a selectively permeable membrane, water molecules diffuse across the membrane in both directions at an equal rate. There is no net movement of water. Osmotic pressure = Measure of the tendency for a solution to take up water when separated from pure water by a selectively permeable membrane. Osmotic pressure can be measured using an osmometer. In one type of osmometer, pure water is separated from a solution by a selectively permeable membrane that is permeable to water but not solute. The tendency for water to move into the solution by osmosis is counteracted by applying enough pressure with a piston so the solutions volume will stay the same. The amount of pressure required to prevent net movement of water into the solution is the osmotic pressure. Cell survival depends on balancing water uptake and loss . Cells can burst if they take on too much water, or collapse if they lose too much.

Downhome example again: you salt fish to preserve it, by reducing the water content to a point where the bacteria that would spoil it cannot live. Osmosis Blood And Diffusion Of Potassium Permanganate Kmno4 Biology Essay Osmosis Blood And Diffusion Of Potassium Permanganate Kmno4 Biology Essay Published: Last Edited: 23rd March, 2015 This essay has been submitted by a student. This is not an example of the work written by our professional essay writers. Osmosis is the movement (natural) of a solvent, in the case of living organisms (water) selectively through a semi-permeable membrane down a water potential gradient. In other words it is the movement of water across a selectively semi- permeable membrane from an area of high water potential (low solute concentration) to an area of low water potential (high solute concentration) (Bowen, 2000). Semi-permeable membrane A membrane is partially (semi) permeable, if it will let in water molecules but not the molecules or ions dissolved in water (the solutes such as sugar molecules). Many cell membranes function in this manner.

Osmosis is there for an important mechanism in the transport of fluids in living organisms (Bowen, 2000). Osmosis: Movement of water across a selectively permeable membrane from an area of low solute concentration to an area of high solute concentration. Key: - Water, o - Solute Osmosis is important in biological systems, as many biological membranes are semi-permeable. 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 wall, tonoplast (vacuole) or protoplast in two ways, either by diffusing across the phospholipids' bilayer directly, or via 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 (Maton et al., 1997). The process of osmosis accounts for many functions that maintain life. In relation to blood cells, blood cells placed in pure distilled water will swell and burst. If these cells are placed in a Hyper osmotic (hypertonic) solution, i.e., the solution has more dissolved particles, salts, sugar, etc., than is in the cells, they will shrivel up (a process called crenation in the case of blood cells). The energy that drives the process of osmosis is called osmotic pressure. In animal (human beings included), the red blood cells are very important to the survival of the organism because they transport oxygen from the gills, skin, or lungs to the cells of the various tissues (muscles, nerves, etc.). These blood cells are transported in a fluid (serum) that has approximately the same salt content as sea water. Effects of Osmosis on Red Blood Cells Red blood cells as in all animal cells don't have cell walls.

In cases of hypotonic solutions, red blood cells will swell up and burst (explode) .when the cell is in danger of bursting due to accumulation of too much water in it, contractile vacuoles will pump out the water out of the cell to prevent it from bursting. In hypertonic solutions, water will diffuse out of the cell due to osmosis and the cell shrinks. For the red blood cell to stay in its normal condition, it's always surrounded by isotonic solution. If the concentration of the cells cytoplasm is lower then medium (the medium is hypotonic) surrounding the cell, then osmosis will result by the cell gaining water, hence the cell will swell up and burst. If the concentration of the water inside the cell is the same as that outside the cell (the medium is isotonic solution), there exists a dynamic equilibrium, meaning the number of cells getting in and leaving the cells is the same hence the cell will retain its original size. The red blood cell retains its shape because of the isotonic nature of the plasma.

If the water concentration inside the cell is higher than that of the medium (the media is a hypertonic solution), hence the number of molecules diffusing out will be more than that entering, and the cell will shrink. The kidneys in the human body provide the necessary regulatory mechanism for the blood plasma and the concentration of water and salt removed from the blood by the kidneys, which is controlled by the hypothalamus. This process of regulating the salty and the mineral salts in the blood is called osmoregulation. Osmosis and diffusion a have related concepts: Both processes involve the movement of materials from an area of high concentration to an area of low concentration. Diffusion involves the movement of chemical molecules from a low concentration to a higher concentration whereas osmosis involves the movement of water molecules from a high to low concentration via a semi permeable membrane. Importance of Osmosis in the animal / human body Salts and minerals are transferred from water through osmosis. Osmosis transfers water through the plasma membrane (which is selective and semi permeable) of the cell. It manages the mixing of water, glucose and salts in the body cells, this is important, otherwise the cells would loose too much water and eventually die.

Hence osmosis plays an important role in keeping the cells alive. Osmosis plays an important role in the functioning of the kidneys, it is also important in the helping to transfer water and various nutrients between the blood and fluid of the cells. People who suffer from kidney diseases depend in kidney machines to remove waste substances (products from their blood, such machines use a process called dialysis, which is similar to the process of osmosis. Salt water fish constantly consume a lot of water, which is released to the environment through osmosis, while fresh water fish don't drink water because their skin is responsible to absorbing water. Diffusion of Potassium Permanganate (KMnO4) Diffusion is the movement of molecules from an area of high concentration to an area of low concentration across a permeable membrane as a result of kinetic energy of random motion. It is a random movement of molecules which is directional from an area of high concentration to an area of low concentration until equilibrium is achieved. Molecules are in a constant state of motion.

For example, if you dissolve KMnO4 in water so that the concentration is initially higher in one part of the water that another, diffusion will occur so that there is a net movement of KMnO4 from area if high concentration to an area of lower concentration. However, if the KMnO4 molecules have a complete even and random distribution through out the water, there will be no movement of KMnO4 in any direction. The rate of diffusion will be affected by properties of: The cell The diffusing molecule Surrounding solution An example is the rate of diffusion or movement of KMnO4 agar will be as follows in table 1. Agar Plates Osmosis - Tutorhub Osmosis What is the definition of osmosis dw999999 in Biology almost 3 years ago Welcome to our free-to-use Q&A hub, where students post questions and get help from other students and tutors. Follow the trail of responses and if you have anything to add please sign up or sign in . You can ask your own question or look at similar Biology questions . Hello dw999999, For AQA and Edexcel GCSE and iGCSE: Water often moves across boundaries by osmosis.

Osmosis is the diffusion of water from a dilute to a more concentrated solution through a partially permeable membrane that allows the passage of water molecules. 13:12 on 25/01/14 This depends slightly on the level you are working at. For GCSE I would say: "The movement of water from an area of high water concentration/low solute concentration to an area of low water concentration/high solute concentration through a semi-permeable membrane" At A level I would say: "The passive movement of water from an area of high water potential to an area of low water potential through a semi-permeable membrane." Claire S. 19:06 on 22/01/14 "Diffusion of fluid through a semipermeable membrane from a solution with a low solute concentration to a solution with a higher solute concentration until there is an equal concentration of fluid on both sides of the membrane" shub91 15:19 on 10/01/14 Osmosis is the net movement of water particles from a high water concentration to a low water concentration, across a partially permeable membrane.

It is basically the same as diffusion but specifically involves water and a membrane which lets some things through and prevents others things from crossing. Dr. Zainab T. 13:21 on 09/01/14 Osmosis is the movement of water molecules from higher concentration towards lower concentration. samia.k 15:19 on 08/01/14 The definition of Osmosis is: The net movement of water from an area of higher water potential to an area of lower water potential, across a partially permeable membrane. Regards, Kenndel. khboulton 21:09 on 05/01/14 Osmosis - the net movement of water molecules through a partially permeable membrane, from an area of high water potential (the higher concentration of water molecules) to an area of low water potential (a lower concentration of water molecules). Water molecules diffuse down this water molecule concentration gradient until there is a balance of water molecule concentration either side of the membrane.

hellouk 15:05 on 05/01/14 Osmosis is the movement of water through a semi-permeable membrane from a region of high water potential (less concentrated) to a region of low water potential (more concentrated). Niki D. 23:42 on 29/12/13 The definition of osmosis is the movement of water from a area of high water potential to an area of low water potential. sofiane 13:18 on 29/12/13 For A level a definition such as this will be great.... Osmosis is the net movement of water from where the water potential is greater to where it is lower through a partially permeable membrane. I specialise in A-level Biology so if you need anything else give me a shout :0) 00:00 on 29/12/13 Osmosis is the net movement of water from an area of higher concentration or water potential to an area of lower water concentration, through a semi- or partially permeable membrane. This is the process by which water enters the roots of plants.

Osmosis will take place until the concentration of water is the same on both sides of the membrane. mabraham 10:55 on 12/11/13 Osmosis is the net movement of water from an area of high concentration to an area of low concentration through a partially permeable membrane. I know that definition can be quite confusing at first but if you break it down it becomes much more simple. A partially permeable membrane is like a set of doors, if you are smaller than the doors (water) you can get through whereas if you are to big (sugar, salt etc.) you are stuck where you are. The mWater moves from an area where there is alot of it to where there is less. Water moves from an area where there is alot of it to where there is less.

Question: What is the name for the movement of water across a partially permeable membrane from an area of high water potential (low solute concentration) to an area of low water potential (high solute concentration)?
Answer: Osmosis