What is Osmosis: Definition and 49 Discussions

Osmosis () is the spontaneous net movement or diffusion of solvent molecules through a selectively permeable membrane from a region of high water potential (region of lower solute concentration) to a region of low water potential (region of higher solute concentration), in the direction that tends to equalize the solute concentrations on the two sides. It may also be used to describe a physical process in which any solvent moves across a selectively permeable membrane (permeable to the solvent, but not the solute) separating two solutions of different concentrations. Osmosis can be made to do work. Osmotic pressure is defined as the external pressure required to be applied so that there is no net movement of solvent across the membrane. Osmotic pressure is a colligative property, meaning that the osmotic pressure depends on the molar concentration of the solute but not on its identity.
Osmosis is a vital process 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 or hydrophobic molecules like lipids as well as to small molecules like oxygen, carbon dioxide, nitrogen, and nitric oxide. Permeability depends on solubility, charge, or chemistry, as well as solute size. Water molecules travel through the plasma membrane, tonoplast membrane (vacuole) or protoplast by diffusing across the phospholipid bilayer via aquaporins (small transmembrane proteins similar to those responsible for facilitated diffusion and 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.

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  1. S

    I What drives osmosis? (Statistics or Dynamics?)

    This letter in PhysRevLett describes molecular dynamics simulations to investigate the underlying factors that drive osmosis. https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.97.024501 Copy on Internet Archive ...
  2. M

    Why don't hydrogen ions have osmotic activity in living organisms?

    Why hydrogen ions dont have osmotic activity in living organisms?
  3. AN630078

    Biology Water Potential and Osmosis Potatoes Investigation

    a) Evaporation will remove water from the test tubes as it turns into water vapour, meaning that the solution will have a greater solute concentration and thus an increased osmotic potential which results in a more negative osmotic potential. Consequently this lowers the solution's water...
  4. liroj

    Why Does Osmosis Stop in Animal Cells?

    I have a question about osmosis that goes a bit deeper than most basic textbooks so I cannot find the answer.Here's the problem: Imagine an animal cell, say a red blood cell, in a slightly hypotonic solution. The water starts to flow in osmotically. The concentration of solute in the cell...
  5. Absentee

    "Regular" filtration with reverse osmosis filter?

    A nanofiltration filter has a pore size around 0.001 micron. Reverse osmosis filters have a pore size around 0.0001 micron. Additionaly, reverse osmosis occurs when a semi-permeable membrane separates solutions of different concentrations so osmotic pressure has to be applied to move water from...
  6. X

    How does water escape the pot?

    I was cleaning up the kitchen, and there was a large pot that had been filled with water to soak in the sink. A rectangular nylon pot scrubber was hanging over the side of the pot, about 2/3 in the pot and 1/3 hanging out. As I ran the tap, the pot filled up and overflowed, but even after the...
  7. A

    What solute won't leak through dialysis tubing

    I purchased dialysis tubing from carolina medical supplies with a molecular weight cutoff of 12,000 to 14,000 MW. I've been using a sugar solution to demonstrate osmosis but I've noticed that if I leave it alone for an hour or two the sugar begins to leak through the membrane. Is there anything...
  8. A

    I How osmotic membranes function

    I've been doing some experiments with dialysis tubing I purchased online and just have some general questions. Firstly how does osmosis work exactly? I read that because there are less free molecules of the solvent on one side that the solvent on the other side flows in but there were lots of...
  9. alexandria

    How can we accurately measure osmosis in a cell?

    Homework Statement Hi, I'm doing a biology course online and I'm specifically learning biochemistry right now. I'm having a problem with the following question related to one type of passive transport in a cell: this being osmosis. This question relates to measuing osmosis (isotonic...
  10. L

    Is Osmosis a Phenomenon of Thermodynamics?

    I have read that osmosis " works like a machine ". It lifts weight ( this is obvious ) on the expense of thermal energy. Does anyone has any thoughts about how it consumes thermal energy? Thank you in advance.
  11. B

    Oxygen Supply for Single-Celled Organisms: Diffusion vs. Osmosis Explained

    Homework Statement Is the oxygen required by the single-celled organisms obtained by diffusion or osmosis through the surface membrane of the cell? Homework Equations The Attempt at a Solution I'm thinking osmosis since there's a membrane through which the oxygen passes. But I've been...
  12. D

    Diffusion vs Osmosis: What’s the Difference?

    Homework Statement What is the difference between diffusion and osmosis? Homework Equations 3. The Attempt at a Solution I am guessing that diffusion means that particles spread out. And osmosis is when particles spred out in a cell membrane. [/B] Osmosis can be "diffusional" but...
  13. N

    What pressure inside that tree trunk?

    Hi, Having a background of horticulture training (NZTCH) and tree specialisation (NSW Arbor Techniques & Tree Surgery), I'm very interested in biomechanics so enjoy books written by authors like Prof. Dr. Claus Mattheck http://www.mattheck.de/english/english2.htm No idea what forum area this is...
  14. M

    Osmosis with two different solutes

    Hi all, This is the situation: Solution A with 200 Osm urea, solution B with 200 Osm KCl, separated by a semipermeable membrane that is permeable to urea but impermeable to KCl. Each solution is in 1 L water. Calculate the equilibrium concentrations of urea and KCl. The numerical answer...
  15. T

    Osmotic Pressure within pressure vessel

    Hi could someone point me in the right direction about the following scenario A high pressure vessel is 100% filled with an incompressible liquid A membrane separates two sides with differing concentrations one (one may be zero) of an impermeable solute. What would occur ? My feeling is that...
  16. U

    Osmosis Between Air And Liquid

    Hi all, In osmosis a solvent moves across a semi-permeable membrane when the solvent is on both sides of the membrane but the concentration of the solute differs. Normally solvent moves from the side with high osmotic pressure (solvent containing less solute) to side containing more solute...
  17. S

    Osmosis when membrane is permeable to both solute and water?

    Hello everyone, Lets say there is a membrane, which has a channel for the solute(eg sodium) and another channel for water Now if I have a hypertonic (more sodium) solution in side A, and hypotonic (less sodium) solution in side B. Which way would water go? * I'm very confused here...
  18. U

    Chemical potential vs hydro-static pressure during osmosis

    So when osmosis between two solutions (separated by a semipermeable membrane),takes place, the solvent travels from the side where its chemical potential is higher to the side where its chemical potential is lower. However, this results in a difference of levels of fluids across the membrane...
  19. D

    Reverse osmosis energy recovery system

    I want to know the possibility for reducing pressure of reject Brine fluid below the inlet pressure of raw feeding water to RO by a pressure exchanger / Energy recovery turbine in Reverse osmosis system. If its possible, how it works? Please help me in this regards. Thank you
  20. M

    How does the entropy behind osmosis work?

    Using a simple example: air, why does it naturally form a uniform mixture? Brownian motion wouldn't differentiate between different gases that make up the air.
  21. C

    Understanding Reverse Osmosis Water Filters: Fact or Fiction?

    HI, this is the first time I have posted on this site. I know very little about physics, so am not sure if this is ok to post here, but I wondered if anyone could tell me if reverse osmosis is a true phenomena and whether reverse osmosis water filters (which you can buy and fit to your taps...
  22. L

    Osmosis and entropy/free energy and mixing.

    I sometimes have trouble with the concept of entropy being a driving force for work being done. For example, during osmosis you can raise the level of water on one side of a semipermeable membrane (i.e. do work) because the free energy of the system is minimized if there is a flow of solvent...
  23. V

    Is osmosis a form of diffusion?

    I am confused because I read that a selectively permeable membrane means that it becomes osmosis and that there can't be a selectively permeable membrane for diffusion. Or is osmosis just diffusion across a selectively permeable membrane?
  24. M

    Osmosis: Diffusive or Something Else?

    So I've been trying to cook up a homework assignment for a class that guides them through deriving osmotic flow from diffusion. I've been working on it for a month, and running into all kinds of stumbling blocks, so I thought I'd ask the simple question here: is osmotic flow fundamentally...
  25. T

    What is the relationship between concentration and water movement in osmosis?

    I don't understand osmosis. According to my textbook, water will flow through a partially permeable membrane from a less concentrated solution of sucrose, to a more concentrated solution of sucrose, even if it means one side of a partially permeable membrane has more water than the other. I...
  26. M

    Reflection coefficient (osmosis)

    hello ppl, i have a question about the reflection coefficient... since the RC indicates the permeabilty of a membrane for a specific molecule...doesnt that mean (If the RC between 0 and 1) that the concentration of that molecule on both sides of the membrane will become the same after a while...
  27. S

    Cause of Osmosis: What's Happening?

    Hello everyone, I'm getting the feeling I have not understood osmosis all this time even though I thought I did. So if 2 solutions are separated by a water permeable membrane, and one solution has less solutes than the other, water would move to less concentrated area right. Now why does this...
  28. T

    Osmosis, osmotic pressure, vapour pressure

    Why does osmosis happens? Does osmosis happens when we have osmotic pressure difference between the two solutions (that are connected by a membrane)? Does osmosis happens when we have two solutions of different concentrations? My professor told that osmosis happens because of the vapour...
  29. menniandscience

    Entropy & Osmosis: Brownian Motion & 2nd Law of Motion

    what exactly browian motion and osmosis does to the second law of motion? nothing right? because anyway one will set an experiment trying to locate semipermeable membrane, he\she already exert more energy. (i need you to verify me) thanks
  30. M

    Reverse osmosis perpetual motion machine

    The original problem was as follows: Closed-loop system, with complete isolation. Salt water is green, fresh water blue, porous plug (AB) is red. Fresh water spills into the salt water column at C if the fresh water is lifted higher than the salt water, maintaining continuous flow...
  31. Y

    Minimum Pressure applied by reverse osmosis?

    Homework Statement Seawater is approximately .60M NaCl. What is the minimum pressure that must be applied at 25 degrees Celsius to purify seawater by reverse osmosis? Assume i=2.0 for NaCl. Homework Equations Osmotic pressure = MRT R= gas constant, .0821 Latm/mol K The Attempt at a...
  32. L

    Potassium chloride vs. Sodium chloride for osmosis?

    Okay, I'm stumped. I've been searching endlessly to find two pieces of information for an Honors Chemistry research paper. My mentor wants to me explain why we used sodium chloride rather than potassium chloride in our potato tuber osmosis experiment. I've searched six hours straight without...
  33. C

    Moral Principles Learned via Social Osmosis

    Moral Principles Learned via Social Osmosis I came across this statement “for everything human beings do by intelligence rather than instinct, any course of conduct they choose when they might have chosen differently, is a moral action” in “The Metaphysical Club” by Louis Menand and it...
  34. R

    Exploring Cell Shrinkage: Plasmolysis, Diffusion, Osmosis, Imbibition

    Plasmolysis, diffusion, osmosis, imbibition My Reason: its the shrinkage of cell. The rest are process involved in the transport of water
  35. Y

    What is the driving force behind osmosis in biology?

    Let's say there are two parts in a container, one part is pure water and the other part is some solution. There is a membrane blocking the solution particles from moving to the other side. So eventually, water will be pulled to the solution side to make it less concentrated. My question is...
  36. F

    Question about osmosis and osmotic pressure

    Hey Was making up some chem notes (mid semester study break, thought id better actually do some) and came across osmosis. Now my understanding of this is that you have two solutions separated by a membrane that let's the solvent pass but not the solute. What i don't get is why the solvent...
  37. C

    Biology: Osmosis & Grocery Store Produce

    We have been workinging lately with osmosis, and we recently did a lab. It involved putting a piece of celery into different petri dishes, which had different solutions. Distilled water with salt, from 0 g/mL to 2. The less salt in the solution, the celery grew, and then at 1.2 it startes to...
  38. S

    Confusing Osmosis: Why Hot Milk Tastes Like Water

    When a closed jar of hot milk is dipped in a cool solution and tasted after some time then why does it taste like water at the bottom.
  39. S

    Osmosis, Solutes, and Solvents

    Are these correct? 1) The rubbing alcohol sold in drug stores often is composed of 70% isopropyl alcohol and 30% water. In this solution a.both water and isopropyl alcohol are solvents. b.isopropyl alcohol is the solvent. c.water is the solvent. d.neither water nor...
  40. E

    Help with a question about Osmosis

    I'm having a difficult time with a question in my homework and I was just wondering if anyone would help me out. The question is: Road salt that has been accidentally spilled on grass often kills grass. Explain why this happens? I think it is because the salt deprives the grass of getting...
  41. R

    Osmosis Problem: Plant Cell Mass & Flaccidity

    hi am i right in saying that if the concentration of sucrose solution becomes more concentrated outside a plant cell, then the plant cell will become flaccid and decrease in mass? Please help need to know urgently thank you
  42. S

    Kill Tumor Cells w/Osmosis: Active Transport Needed?

    Could a tumour cell be killed in a person by making the cell membrane too permeable to water and so causing tumour cells to swell and burst.Perhaps active transport of some kind would be needed to do this?
  43. D

    Rank Osmosis Scenarios & Define Osmosis

    Hey guys can someone help me with the osmosis scenarios and rank them in order of the most mass gained and also write a good definition of what osmosis is thanks. thanks first of all i have the following solutions i have 5% sucrose in dialysis tube in distilled water - cup 1 i have 10%...
  44. D

    OSMOSIS what do you expect to happen

    OSMOSIS! what do you expect to happen! Hey guys can someone help me with the osmosis scenarios and rank them in order of the most mass gained and also write a good definition of what osmosis is thanks. thanks first of all i have the following solutions i have 5% sucrose in dialysis tube...
  45. K

    Restoring Wilted Flowers with Osmosis: The Best Soaking Solution

    Quick Quick Need Help Osmosis! Hi i need help answering these questions... You can restore wilted flowers or vegetables by soaking them in water. From your knowledge of osmosis, would it be better to saok them in distilled or tap water? Explain why it is important for intravenous fluids...
  46. T

    Osmosis & Potato Chip: Exploring Deeper Meaning

    Hi.. I am currently doing an experiment on Osmosis - Potato Chip, Looking at the effect of osmosis etc, However I was curious whether there was an inner depth to this, So far were ever I look the only defination of Osmosis is higher concentration to lower, but within my prediction I would like...
  47. N

    Osmosis is the passage of water from a region of high water

    Osmosis is the passage of water from a region of high water concentration through a semi-permeable membrane to a region of low water concentration. .My question is why high water potential flows water to low water potential. What makes this occurs ? Also, does enzyme still works after being...
  48. P

    Can water or alcohol be absorbed through the skin with osmosis?

    Can water or alcohol be absorbed through the skin with osmosis? More importantly can it be absorbed into the bloodstream? I know some chemicals can be, what characteristics allow those chemicals to do that? Pan
  49. Link

    The Science Behind Salt and Wounds: Osmosis?

    Why does the wound hurt more if you pour salt (NaCl) on it? Does it have something to do with osmosis?