How do we define a process of diffusion or osmosis?
Diffusion is a process by which solute particles moves from higher concentration to lower concentrations.
When we place the dry raisin in water, do we call it a diffusion or osmosis?
It is a process of diffusion as membrane of raisin is no more intact (it has been broken while drying the raisin) so, now the solute/sugar which is present in raisin will move out of the raisin (and makes water sweet in taste) and water from outside will move inside the raisin till equilibrium is reached and so eventually the raisin will swell up.
Osmosis is diffusion of solvent through a semipermeable membrane. If the membrane allows solutes to diffuse too, then it is called a differentially permeable membrane. Plasma membrane is a differentially permeable membrane. However, semipermeable membrane is a membrane which allows only solvent molecules to diffuse through. All biological membranes are differentially permeable. Semipermeable membranes can be created artificially.
Can we define osmosis in terms of pressure?
Let’s say we have two chambers that are separated by semi-permeable membrane (which will allow some particle to pass through it), both sides has some hydrostatic pressure but if we provide external pressure/osmotic pressure at one side, the water molecules will move from lower concentrations (of water) to the higher concentration of water and that is called Reverse Osmosis (that we frequently hear from people about the RO water).
Common misconceptions in biology: Misconceptions around diffusion and osmosis - IndiaBioscience
Many biological phenomena, like respiration, osmoregulation or nerve conduction, have a basis in physical processes like diffusion and osmosis. Definitions and diagrams may contain nuances that students may miss, especially when these are not viewed through the lens of physics. In this article, Nagarjuna G, Former Professor, Homi Bhabha Centre for Science Education, TIFR gives examples of some of these misconceptions and offers simple simulations to provide a more accurate picture of these processes.
Archives of CUBE Context 2 Curriculum Whatsapp group discussion
[16/08, 00:37] Shalini Sharma CUBE: Definitions imply that a process is a diffusion when the solute moves from higher concentration to lower, and it is osmosis when the solvent moves from higher to lower concentration (but only when a semi-permeable membrane is present)!
Are these definition really true about osmosis specifically about the semi-permeable membrane, does not these solvent molecule move even when there is no semi permeable membrane?
Let’s take an example of water and NaCl (which is going to ionize in Na+ and Cl-), what will happen to their movement through semi-permeable membrane? All Na+, Cl-, and H2O can move through this semi permeable membrane. if not why? And if yes, why?
[16/08, 01:14] Theertha CUBE: What will happen if we soak a dried grapes in a water for three days !? Which one is the solute &solvent in this case !?,(Taken from my phone’s gallery, i guess this was in 3 constitutive days ,not sure!!!)what do you think @shalinisharma98 @Himanshu @PChitralekha @Theertha and others
[16/08, 09:05] +91 99106 87801: Osmosis is diffusion of solvent through a semipermeable membrane. If the membrane allows solutes to diffuse too, then it is called a differentially permeable membrane. Plasma membrane is a differentially permeable membrane.
[16/08, 09:17] Shraddha Sonawane: Sugar present in this raisins will be act as solute and water present in the glass will be solvent.
Here, solutes are in more concentrate inside raisins compared to water so, water will enter inside raisins and raisins become swell.
[16/08, 09:19] Shraddha Sonawane: What was your objective while performing this experiment?
[16/08, 09:21] +91 99106 87801: The solutes are the sugars etc. present in the raisins and the solvent is water. There is simple diffusion of water and also solutes (after sometime the water tastes sweet) and not osmosis as there are no intact membranes (the drying as damaged the membranes).
[16/08, 09:24] +91 99106 87801: And since diffusion of water into raisins will continue till equilibrium is reached, raisins swell.
[16/08, 09:25] Theertha CUBE: ma’am .Then there is no osmosis without diffusion !!!Is there any case where osmosis happens and diffusion not !?@~Chitra @Shalini Sharma CUBE @Shraddha Sonawane
[16/08, 09:26] +91 99106 87801: I have a problem with defining diffusion and osmosis in terms of concentration
[16/08, 09:27] +91 99106 87801: My definition says osmosis is a process of diffusion. So how can osmosis occur without diffusion?
[16/08, 09:29] +91 99106 87801: Is there any way I can reverse the process of osmosis, i.e. make solvent move from a lower concentration to higher concentration?
[16/08, 09:30] +91 99106 87801: It is diffusion, said to make it clear. Are there different types of diffusion?
[16/08, 09:31] Theertha CUBE: can we exert external pressure !?
[16/08, 09:32] +91 99106 87801: 
so why are we defining in terms of concentration. How shoul we actually define diffusion and osmosis?
[16/08, 09:33] +91 99106 87801: External pressure where and why should that reverse the processes?
[16/08, 09:36] Theertha CUBE: Solvent can’t move from lower concentration to higher concentration ,so we need an extra support like a force like pressure to be exerted and reverse the process !?
[16/08, 09:37] Theertha CUBE: ma’am, can you give a example in which semipermeable membrane have a role !!! In raisins case there is no semipermeable membrane .What actually this semipermeable membrane stands for !?
[16/08, 09:37] +91 99106 87801: Pressure is exerted on the solvent at lower or higher concentration?
[16/08, 09:41] +91 99106 87801: As I said, semipermeable membrane is a membrane which allows only solvent molecules to diffuse through. All biological membranes are differentially permeable. Semipermeable membranes can be created artificially, not aware of any naturally occurring semipermeable membrane.
[16/08, 09:43] +91 99106 87801: This I am saying when considering cellular environment
[16/08, 09:45] +91 99106 87801: If a solute is taken which is larger than the pores in the membrane and there are no transporters in the membrane to transport them, then the membrane becomes semipermeable.
[16/08, 09:52] +91 99106 87801: There is also the aspect of osmotically active solutes. If starch solution or water with oil droplets is separated from water by a semipermeable membrane, will osmosis occur?
[16/08, 09:55] Rahul Kushwaha CUBE: Yes, that’s exactly how we purify water for drinking purposes. There is a machine that does this work for us. It’s called a RO water purifier.
PS: RO stands for Reverse Osmosis
[16/08, 10:10] Shraddha Sonawane: okay maam, in a passive transport there are diffusion and osmosis. then diffusion is further divide in Simple diffusion and facilitated diffusion.
[16/08, 10:14] Shalini Sharma CUBE: Ma’am, but then what will be condition if semi-permeable membrane is not here, can we still say a process as osmosis? Because even in the absence of semi-permeable membrane, these water molecules are moving along with the solute molecule.
[16/08, 10:14] Shalini Sharma CUBE: Osmosis is a type of diffusion, so if we are saying osmosis… diffusion automatically comes.
[16/08, 10:15] Theertha CUBE: So osmosis occur in lower to higher concentration through semipermeable membrane ( I thought Higher to lower) .In reverse osmosis that occur from higher to lower .But, actually solute ( impurities) must be removed from water like higher solute to lower solute concentration region !! So there also diffusion happening in reverse osmosis 
@~Chitra @Rahul Kushwaha CUBE @Shraddha Sonawane @Shalini Sharma CUBE
[16/08, 10:16] Theertha CUBE: So, where ever osmosis occuring there must be diffusion too!?
[16/08, 10:17] +91 98677 29984: Diffusion involves the movement of both solute and solvent molecules. Whereas, osmosis involves the movement of only solvent molecules.
[16/08, 10:19] Shalini Sharma CUBE: Can we say if we have two chambers that are separated by semi-permeable membrane (which will allow some particle to pass through it), both sides has some hydrostatic pressure but if we provide external pressure/osmotic pressure at one side, the water molecules will move from lower concentrations (of water) to the higher concentration of water.
[16/08, 10:39] +91 99106 87801: molecules with higher free energy move toward molecules with lower free energy. In a solution, the free energy of water molecules is decreased because the movement of water molecules is restricted by the presence of dissolved solutes. So when such a solution is separated by a semipermeable membrane from water without dissolved solutes where the free energy of water molecules is higher, these higher energy water molecules will diffuse towards the lower energy water molecules in the solution (osmosis). When pressure is put on water with dissolved solutes, the free energy of water molecules increases, and the minimum pressure required to equalise the free energy of water molecules in solution with that of water molecules without the dissolved solutes and prevent any osmosis from occurring is called the osmotic pressure. If more pressure is put on the solution, the free energy of water molecules in solution increases as compared to that of water without the solutes and water from solution moves towards pure water (reverse osmosis).
[16/08, 12:54] +91 99106 87801: Free energy of water molecules in solution is inversely proportional to concentration of solute, more the number of dissolved solute molecules, more is the energy spent by water molecules to maintain the solute molecules in solution/ in dissolved state and so less is the free energy available with the water molecules. Water molecules spend free energy in holding the solute molecules in a dissolved state.
[16/08, 14:45] Himanshu CUBE: When will the process of water entering inside the resin stop?
@Shraddha Sonawane
[16/08, 15:24] Shraddha Sonawane: I think, till equilibrium not reached, water will enter inside raisins.
Once equilibrium reached it means amount of solute and solvent get equal then entry of water will stop.
[16/08, 15:30] Himanshu CUBE: Great, Is this phenomenon called osmosis or is it diffusion?
And then why the water, eventually turns sweet as per @~Chitra maam
@Shraddha Sonawane @Shalini Sharma CUBE @Theertha CUBE
[16/08, 15:54] Shalini Sharma CUBE: Do we really use the term stop here, because the article written by GN sir and in some books also there is mention of dynamic state of particles which means the molecules that are present in solution are continuously moving because of the kinetic energy that they have and even after the equilibrium, these molecules keep on moving…it is just that the net flow of molecule from one side to another will be equal and that’s why we are saying that equilibrium has reached.
[16/08, 15:56] Shalini Sharma CUBE: It is diffusion, as described by ma’am, while drying up their membrane damages and so there is no semi-permeable membrane. So, solute can go from inside the raisins to the water in glass (that’s why it taste sweet) and water from the glass can move into the raisin. Both ways solute and solvent can move.
[16/08, 16:07] Himanshu CUBE: Do you mean amount of solute and solvent both inside and outside the rasin becomes equal?
I.e the concentration sugar solution both inside and outside becomes same…
In this case nobody moves neither solute nor solvent
If nobody moves then where is the point of kinetic energy coming suddenly out of the blue
Comments please
@Shalini Sharma CUBE
[17/08, 22:55] Shalini Sharma CUBE: Yes sir, I was considering the same as you mentioned about the same concentration of both solute and solvent. However, still some molecules can go from A side to B and vice-versa which means net tranfer of molecule is same but molecule are still moving.
[18/08, 09:42] Himanshu CUBE: Why should a molecule move across a semipermeable membrane in first place…
Due to differences in concentration I guess … Am I right?
Once equilibrium is achieved only very miniscule amount of molecules will move.
Why are we worried about such molecules which are very less in number?
@Shalini Sharma CUBE
[18/08, 10:46] Arunan MC: So what were the gaps and misconceptions in this area?
Have been able to pin point?
What were your TINKE moments? Or, are you still confused on Osmosis and diffusion including the role of semipermeable membrane in all this talk? @Shalini Sharma CUBE
[18/08, 10:49] Arunan MC: Please rewrite what were you confused about and what are you still confused about diffusion & osmosis. @Shalini Sharma CUBE
Let’s even write and publish an article on this theme. 
@Shalini Sharma CUBE @Theertha CUBE @Himanshu CUBE and others.
[18/08, 12:06] Himanshu CUBE: Let’s write a blog in metastudio in the week of Independence day.
And get independence from the misconceptions we have on the topic of Diffusion and osmosis
@Shalini Sharma CUBE @Theertha CUBE @Dhanraj and others
[18/08, 17:23] +91 99106 87801: When water solution with solute molecules and water are separated by a semipermeable membrane (allows only water molecules to pass through), equilibrium will not be reached unless pressure is applied on the solution. In which case, even after equilibrium is reached, because of their kinetic energy, water molecules from both the sides of the membrane will continue to move across the membrane without changing the concentration/free energy of molecules i.e. the number of water molecules moving from solution to water will be equal to number of water molecules moving from water to solution.
[18/08, 17:42] Theertha CUBE: Diffusion and osmosis
Osmosis is a type of diffusion .
Also we can talk in terms of gradient !,gradient can be concentration ,pressure etc.simply an energy!? @~Chitra
Diffusion is not limited to solute,otherthan diffusion can be a movement of solute and solvent from higher concentration to lower concentration .
If there any semipermeable membrane comes that is the case for osmosis .
Reverse osmosis is the process in which water purification occur .Where solvent molecule moves from lower to higher concentration through a semipermeable membrane @Rahul Kushwaha CUBE @Shraddha Sonawane @~Chitra .
Diffusion is of two .
Simple diffusion
movement of solute & solvent from higher concentration to lower concentration
Facilitated diffusion
Here a carrier proteins are involved in the movement of solute & solvent from higher concentration to lower concentration. How Cartier protein help in this case @Shraddha Sonawane @Shalini Sharma CUBE
Plases correct me @~Chitra @Himanshu CUBE @Shalini Sharma CUBE &others
[18/08, 17:57] Arunan MC: lease give simple examples of solute and solvent and also if possible let’s recall what we forget easily on the calss 8th Thistle funnel experiment.
@Himanshu CUBE @~Chitra @Shalini Sharma CUBE @Shraddha Sonawane and others.
[18/08, 18:25] Himanshu CUBE: What is meant by kinetic energy of water molecule.
Classical definition goes like this :The energy of any molecule by virtue of its motion is called kinetic energy of that molecule…
In the case of osmosis just because of gradient in concentration the solvent I.e. water only moves towards the area where the solute concentration is more. As a result, eventually both the solutions separated by a semipermeable membrane would attain same concentration.
Once this state is achieved why will water move one side to another and vice versa.
Does that really happen? Can somebody give reference for this exchange of water due to kinetic energy
[18/08, 18:56] +91 99106 87801: Even without a concentration gradient, molecules are in motion due to kinetic energy. So water molecules from solution as well as pure water tend to move across the membrane. As long as solute molecules are present, water molecules have lower energy and there will be a net (more) movement of molecules towards the solution side. Equilibrium will not be reached ever if the membrane is a semipermeable one which doesn’t allow solute molecules to move across the membrane.
[18/08, 21:16] Himanshu CUBE: Why must equilibrium won’t ever reach when solutions are seperated by a semipermeable membrane?
[18/08, 21:31] +91 99106 87801: We are talking about pure water and water with solute molecules. However many water molecules move in to the solution, the solute molecules will still be there to reduce free energy of water molecules. Unless all solute molecules disappear, how can pure water equilibrate with a solution?