Osmosis - Online Tutor, Practice Problems & Exam Prep

Osmosis is the diffusion of a solvent, typically water, across a semi-permeable membrane, which allows certain small molecules to pass while blocking others like ions or large molecules. This process is driven by the concentration gradient, where the solvent naturally moves from a region of lower solute concentration to one of higher concentration, eventually reaching equilibrium. At equilibrium, osmotic pressure, the force exerted by the solvent on the membrane, halts further net movement of the solvent. Understanding tonicity is crucial as it determines the direction of solvent flow; hypotonic solutions have lower solute concentration and osmotic pressure, isotonic solutions have equal concentrations and pressures, and hypertonic solutions have higher values compared to bodily fluids. These principles are vital in biological systems, where the tonicity of the environment can cause cells to swell and potentially burst in hypotonic conditions, remain stable in isotonic settings, or shrink and dehydrate in hypertonic environments.

Osmosis Concept 1

Osmosis is the net movement of a solvent, usually water, across a semi permeable membrane. Now this semi permeable membrane is just the material that's allowing solvents in other small molecules to pass across. And we're going to say that these cell membranes are around living, that are around living. Cells are in fact semi permeable themselves.

Now these cell membranes, they prevent solutes from passing through and these solutes can be ions or large molecules. Now if we take a look here at this illustration of a semi permeable membrane, here the membrane is asking if you have an appointment. This larger molecule in red is trying to get through and they can't get past the barrier.

But the smaller ones down here do have an appointment are allowed to pass through because they are the right size and they can pass through the semi permeable membrane to the other side. And this is the way that semi permanent membranes work. Osmosis is the movement of water. Net movement of water but semi permeable membranes can halt and stop certain molecules from traversing from one side to the other side of a living cell.

Osmosis Concept 2

All right everyone. So at this point we can say that the solvent moves from a lower concentration solution to a higher concentration solution and eventually equilibrium is reached and the net flow of solvent is stopped by osmotic pressure. Now what exactly is osmotic pressure itself? Well, it's the counterforce required to stop the flow of solvent through the semi permeable membrane.

So let's pretend that my hand is this semi permeable membrane and we have the flow of water on this side is less concentrated over here on the other side of the semi parallel membrane, it's more concentrated. Water's going to want to flow through this semi permeable membrane to the other side. Now as water's flowing through, there's going to be some resistance. There is a pressure that's on this side of the semi permeable membrane. That pressure is osmotic pressure.

So the solvent's passing through the semi permeable membrane trying to go from the less concentrated solution to the more concentrated solution. But my osmotic pressure that's building behind here is trying to stop the flow of water or the flow of solvent. OK. So that's what osmotic pressure is. It's the counterforce that's pushing against the sulfur that's coming through the descending parallel membrane.

Now if we take a look here at this image, we have these little blue spheres which represent our solvent molecules and then we have our solute molecules. If we take a look at our two images, we can say in the top part we have how many solute particles. We have 123-4567 of the solute particles and then we only have 3 solvent. Then if we look at the bottom part we have what 2 solute and we see that we have way more solvent, a ton. So actually let's count. We have 123456789101112131415, right? So we have 15 solvent.

We didn't really need to count. We can already see there's way more solvent than solute. We can say that the bottom part is the part that is less concentrated because there's way more of our solvents there. So it's the lower concentration solution. The top part has way more solute than solvent, so it's the more concentrated or higher concentration solution. So that means water is going to flow naturally from the lower concentration side to the higher.

So water is going to move this way as it's moving through this semi permeable membrane here. Remember, there's going to be that force that's kind of trying to stop the flow of water. That's the osmotic pressure. It's building on this side here. Because remember, what's the ultimate goal of osmosis? The ultimate goal of osmosis is to get both sides to have the same equal solution concentrations.

And we're going to say the bigger the difference in solution concentrations on both sides, then the higher the osmotic pressure needed to stop this flow of solvent, right. So that's what we'd say in terms of this particular image. If we go to the other side, what do we see? Well if we go to the other side we have 123-4567 solute and then solve it we have 1234567891011121314 which is basically a one to two ratio one solute for every two solvent.

If we look here, we have what we have 2 solute and four solvent. The numbers are smaller, but if we are paying attention here, we can see the ratio is still the same. It's still a one to two ratio, it's still 1 solute for every two solvent. So all the numbers look different. The ratios are the same, so the concentrations on both sides are the same. OK. So we'd say that there is no net flow between the two because both sides already have equal solution concentration.

Alright. So here we wouldn't talk about the flow of solvent. Alright. So just remember this is what we're talking about. Osmosis is the flow of water from a lower concentration or less concentrated side to a more concentrated side. And as it's passing through the semi permeable membrane, there is an osmotic pressure that's kind of trying to stop that flow of solvent.

Osmosis Example 1

Here osmosis is best defined as the movement of SO. Remember osmosis is the movement of a solvent across a semi permeable membrane. Our solvent typically is water, so it's a movement of water molecules.

So that means B&C are out and let's see across a semi permeable membrane into a region of low solute concentration. No, not low high. Because of that A can't be the answer.

Therefore D is the correct one where water molecules move across a semi membrane into a region of high solute concentration. So here option D would be the correct answer.

A semipermeable membrane is placed between the following solutions.

Which solution will increase in volume?

• A. Solution A:6.78% NaCl
• B. Solution B:12.7% NaCl

Four U tubes each have distilled water in the right arm, a solution in the left arm, and a semipermeable membrane between the arms. If the solute is LiF, which solution is most concentrated?

• A.
• B.
• C.
• D.

Identify the direction of water flow between 2 solutions separates by semipermeable membrane, where  are the solute particles.

• A. water will flow from solution A to solution B due to higher osmotic pressure on the solution B.
• B. water will flow from solution A to solution B due to lower osmotic pressure on solution B.
• C. water will flow from solution B to solution A due to lower osmotic pressure on solution B.
• D. water will flow from solution B to solution A due to lower osmotic pressure on solution A.
• E. water will not flow because both solutions have the same osmotic pressures.

Osmosis Concept 3

We know that osmosis is the movement of a solvent from an area of low concentration to an area of high concentration. Now the direction of solvent flow depends on tonicity. Tonicity itself is just the relative concentration of solutes dissolved in the solutions, and when we take a look at the different types of solutions, realize that we're looking at solution solute concentration and osmotic pressure relative to one another.

Have we take a look? Here we have our hypotonic solution, our isotonic solution, and our hypertonic solution with a hypotonic solution. It has a lower solute concentration and lower osmotic pressure relative to bodily fluids. And when we talk about isotonic solutions, this is when two solutions have the same solute concentration and osmotic pressure. Now an interesting piece of information is when we deal with intravenous solutions, they must be isotonic to bodily fluids such as blood, plasma, tissue cells, tissue fluids, etcetera.

And then finally, we have hypertonic solutions, which has a higher solute concentration and osmotic pressure relative to body fluids. Now if we take a look here, we're going to talk about hypotonic, isotomic and hypotonic environments and look at them in reference to their solute concentrations outside the cell, osmotic pressure outside the cell and the effects they have on red blood cells. So when we're looking at hypotonic solutions, we're going to say they have lower solute concentration. We said isotonic, they would have equal solute concentrations between two things being compared to one another. Hypertonic would have higher solute concentration.

Now what about their osbotic pressure outside the cell? Well, lower solute concentration would result in lower osmotic pressure. Here, the equal amount of solute concentration would equate to an equal osmotic pressure. Higher higher solute concentration will result in higher osmotic pressure. What effect does this have on a biological system such as a red blood cell? Well, here we're going to say that we have a lower concentration on the outside. So that would mean that it's more concentrated within the red blood cell. So remember, osmosis moves to where it's higher in concentration, so water would enter the cell. This causes a process known as hemolysis. So basically the cell will swell up because all the water is going in there and if too much water gets in there it can burst. OK, so the cell will swell and then could burst.

Next we have an isotonic environment, so the concentration inside and outside the red blood cell are the same. So water enters and exits the cell at equal rates. So there is no net movement of water. The same amount that goes in is the same amount that comes out finally. If we're in a hypertonic environment, that means that it's more concentrated on the outside of the red blood cell, so water is going to exit the cell. If enough water exits the cell, this causes creation, so the cell will dehydrate and it shrivels.

Now, how's the way for us to remember these different types of situations? Well, here let's say we're looking at a hypotonic environment. So a hypotonic environment. Hypo sounds close to hippo, hippos drinks. A hippo drinks too much water, and swells like a cell. So hippos were taking a huge amount of water because the environment is hypotonic and they could burst or swell hypertonic environments so the outside is more concentrated than the red blood cell. So a hypertonic environment can be related to a hyper kid. The hyper kid playing outside gets dehydrated like a cell. So if your environment is hypertonic, you're going to lose water out of your red blood cell. It's going to exit the red blood cell and try to dilute the outside environment. So just keep these little memory tools to help you know the distinction between hypotonic versus hypertonic isotonic. We know everything is equal on the inside and out, so there's no net movement of water.

Osmosis Example 2

Here it says label the tenacity of the solution outside the cell where the dot, the purple dot are the solute particles. All right, So what we have to do is we have to look at how many dots we have on the outside and compared to the number of dots on the inside.

In the first image we can see that inside the cell is more concentrated, Outside the cell is less concentrated, it has less purple dots. Remember we have to discuss what's what type of solution is on the outside. Since the outside is less concentrated, it is a hypo⁢tonic solution.

For the second one, both the inside and the outside have 5 purple dots, so 5 solute molecules. They're equal inside and out, so this would have to be an iso⁢tonic solution.

And then finally here we have the outside having more dots, so outside is more concentrated. Since the outside is more concentrated, this represents a hyper⁢tonic solution. So just remember, we're looking at what the solution is on the outside relative to what's inside a particular cell.

If the fluid surrounding a patient's red blood cells is depleted in electrolytes, is crenation or hemolysis more likely to occur?

• A. crenation
• B. hemolysis

A solution with the same osmotic pressure as the blood is

• A. isotonic to the blood
• B. hypotonic to the blood
• C. hypertonic to the blood
• D. nontonic to the blood.

A red blood cell placed in pure water will swell because:

• A. the osmotic pressure is greater in the water than in the cell.
• B. the osmotic pressure is greater in the cell than in the water.
• C. the osmotic pressure is the same in the cell and the water.
• D. water moves from a higher osmotic pressure to a lower osmotic pressure.
• E. the vapor pressure of the water in the cell is greater than the vapor pressure of pure water.

Here’s what students ask on this topic:

What is osmosis?

Osmosis is a fundamental biological process where solvent molecules, typically water, move across a semipermeable membrane from a region of lower solute concentration to one of higher solute concentration. This movement aims to equalize the solute concentrations on the two sides of the membrane. The semipermeable membrane allows the passage of the solvent (water) but not the solute (like salt or sugar).

This process is vital for maintaining the proper balance of fluids in cells and across cell membranes. It's also how plants absorb water from the soil, and it plays a critical role in kidney function and the purification of blood. In essence, osmosis helps regulate the internal environment of living organisms, contributing to homeostasis, which is the stable, balanced state of biological systems.

What is reverse osmosis?

Reverse osmosis is a water purification process that removes contaminants from water by using pressure to force water molecules through a semipermeable membrane. The membrane is designed to allow water molecules to pass through while blocking larger molecules and ions, such as salts, bacteria, viruses, and chemicals.

During the process, pressurized water is pushed against the membrane. Pure water flows through the tiny pores in the membrane, while contaminants that are too large to pass through the pores are left behind and flushed away. This results in two streams of water: the purified water, which is collected for use, and the waste stream, which contains the concentrated contaminants.

Reverse osmosis is commonly used for drinking water purification, in the production of bottled water, and in various industrial processes that require high-quality water. It's particularly effective in desalinating seawater, making it an important technology in areas where fresh water is scarce.

What is the difference between osmosis and diffusion?

Osmosis and diffusion are both processes that involve the movement of molecules, but they differ in key ways. Diffusion is the process by which particles spread from an area of high concentration to an area of low concentration, until they are evenly distributed. This movement is driven by the kinetic energy of the particles and occurs in gases, liquids, and solids.

Osmosis, on the other hand, is a specific type of diffusion that involves the movement of water molecules across a semipermeable membrane. In osmosis, water moves from an area of low solute concentration (where there is more water) to an area of high solute concentration (where there is less water), until equilibrium is reached. This process is vital for maintaining the proper balance of fluids in cells and is critical for various physiological functions in living organisms.

How does osmosis work?

Osmosis is a type of passive transport, meaning it doesn't require energy from the cell. It specifically refers to the movement of water molecules through a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration. The semipermeable membrane allows the passage of water molecules but not solute molecules.

Here's how it works: Imagine two solutions separated by a semipermeable membrane. One side has a high concentration of solute (like salt) and, therefore, a lower concentration of water. The other side has a low concentration of solute and a higher concentration of water. Water molecules will move from the side with more water (less solute) to the side with less water (more solute). This movement continues until the concentration of water and solute equalizes on both sides of the membrane, reaching a state of equilibrium.

Osmosis is crucial for maintaining the proper balance of fluids in cells and is fundamental for various physiological processes in living organisms.