In this video, we're going to do a quick refresher on osmosis. So you guys know that osmosis is simply a type of diffusion. And diffusion is the movement of a substance from high concentration down to lower concentrations of the same substance. And osmosis again is a specific type of diffusion. And so osmosis is the diffusion of a solvent across a semipermeable membrane or a membrane that allows some substances to cross but prevents other substances from crossing. And so the solvent is usually going to be water, especially in biological systems. And osmotic pressure is the pressure that's required to prevent the flow of the solvent. And so really osmotic pressure is a measure of the strength of osmosis. So the higher the osmotic pressure, the greater the strength of osmosis. Now in our next video, we're gonna talk about the direction of osmosis. But before we get there, it's important to note that osmosis direction depends on the tonicity of the solution. And so recall that the tonicity refers to the relative concentrations of solutes, not solvents that are dissolved in the solutions. And so really there are 3 different terms that refer to the tonicity of a solution, and those three terms are isotonic, hypotonic, and hypertonic. So isotonic refers to a solution that has the same solute concentration as another solution. And again, solute here is important because tonicity refers to the solute concentration, not the solvent concentration. So the next term is going to be hypotonic. And so hypotonic kinda sounds like low, hypo, low. So hypotonic solutions have lower solute concentrations than another solution. And the opposite of of hypotonic is going to be hypertonic. And when I think of hyper, I think of a kid that's had way too much sugar and they're just running around all over the place. And so because they've had too much sugar, hyper, this is a solution that has a higher, solute concentration than another solution. And so what's really important to note is that these three terms here are words of comparison, so you can only use them when you're comparing one solution to another solution. So in our example below, we're gonna compare the outside solution of a cell to the inside solution of a cell, which is separated by a plasma membrane. And so we're going to label the tonicity of the outside solution. So in our first scenario of our example, the outside solution which is in light blue is separated by a semipermeable membrane and the inside solution is in the yellowish like orangeish brownish type color here, mustard color. And we have these green solutes that are dissolved. And so, notice that the outside solution has a lower solute concentration than the inside solution because there's less green dots in, a certain area. And so because the outside solution has a lower solute concentration, it's going to be hypotonic in comparison in comparison to the inside solution. Now over here in the next scenario, notice that the concentration of solutes, these green dots here, is exactly the same on the outside and the inside solution. So that means that the outside solution is isotonic with respect to the inside solution. And then in our final scenario over here, notice that the outside solution has a much greater solute concentration than the inside. And so because the outside has a higher solute concentration, it's going to be hypertonic. And so, again, the tonicity here is gonna control the direction of osmosis. And we'll talk about the direction of osmosis in our next video. So I'll see you guys then.
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concept
Osmosis Direction
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4m
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Video transcript
So now that we've reviewed tonicity, we can talk about osmosis direction. And recall that osmosis is simply the diffusion of a solvent across a semi movement across this semipermeable membrane. And so if you tend to get confused on this, here's all you guys need to remember. Water will always move from hypotonic solutions towards hypertonic solutions. And this is true when the solutes cannot diffuse across the membrane. And so instead of the solutes diffusing, the solvent or water will diffuse. And water's always gonna diffuse towards the more concentrated solute solution or towards the hypertonic solution in order to dilute the solutes until that solution is isotonic with respect to the solution that the water traveled from. And so, if we look at our example down below, notice that the water flow or the water movement is always going to be in the same direction here. It's gonna flow from hypotonic solutions towards hypertonic solutions. And so if you can remember, hypo to hyper, you'll be good on all of your osmosis direction questions. And so, one thing that students tend not to realize is that water still moves from higher concentrations of water towards lower concentrations of water. So water is still diffusing in the normal way that we think of diffusion. And so, hypotonic solutions we know have lower solute concentrations, but they actually have higher water concentrations. And hypertonic solutions, we know have higher solute concentrations, but they actually have lower water concentrations. And so down here, what we'll see is, hypotonic solutions have low solute concentrations, but they have higher water concentrations. And hypertonic solutions have higher solute concentrations, but they have lower water concentrations. And so water is still moving in the same direction, from high concentration of water to low concentration of water, but still from low concentration of solute to high concentration of solute. So it's just moving in the same direction here. And so if we apply these rules to our scenarios from above from our previous video, which we already completed here, we labeled the tonicity of the outside solution. And so we said that the outside solution in the first scenario was hypotonic, so we'll put hypo on the outside. And that means, of course, that the inside is gonna be hypertonic. And so recall that water flows from hypo towards hyper. So the water flow is gonna go across the membrane in this direction towards the hypertonic solution, and so water is gonna flow into the cell. And if water flows into the cell, that means that the cell can expand in its size. And over here in our second scenario, we said that it is isotonic. The outside is isotonic isotonic with the inside. And so what that means is that water flow is actually going to go in both directions at an equal rate. And so it's not that there's no water movement, it's that the water movement goes equally in both directions. So water is always moving across the membrane no matter what. And then in our last scenario over here, what we said is the outside solution is hypertonic, And of course, that means that the inside of the cell has to be hypotonic. And so water again is going to move from hypo towards hyper. And so it's going to move from the hypo here towards the hyper. That means it's moving outside of the cell. And so if water leaves the cell, that means that the cell could dehydrate and it's gonna shrink up and shrivel. And so, we're gonna talk more about the results of osmosis in our next video. So I'll see you guys in that video.
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concept
Results of Osmosis
Video duration:
6m
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Video transcript
So in our last lesson video, we said the direction of osmosis is impacted by the tenacity of the solutions, and water always flows from hypotonic solutions towards hypertonic solutions. And so the direction of osmosis will impact the results of osmosis, and that's what we're gonna focus on in this video. Now, when cells are placed into hypotonic environments, that causes the cells to swell up just like a hippo. And that's because when the environment is hypotonic, that means that the inside of the cell will be hypertonic. And again, water always flows from hypotonic solutions towards hypertonic solutions. So water would flow into the cell and cause the cell to swell up just like a hippo. And so when the cells continuously swell up, that could potentially cause the cells to lyse or rupture slash burst, and that's because the membrane is expanded too much. Now recall from your previous bio courses that cells with cell walls will actually not lyse in hypotonic solutions, and that's because the membrane expansion is prevented by the cell wall. Now hypotonic environments are actually preferred by plant cells which have cell walls, and that's due to the increased turgor pressure. And recall from your previous bio courses that turgor pressure is literally just the water pressure applied on the cell membrane, pushing the cell membrane up against the inside of the cell walls. And the turgor pressure is really what gives lots of plants their ability to maintain their structures. And we'll be able to see an example of turgor pressure down below in our image. Now, with hypertonic environments on the other hand, hand, that causes cells to dehydrate just like a hyper kid would get dehydrated pretty quickly. And so over here we have an image of a crazy hyper kid that I would hate to babysit over a weekend. And so this hyper kid is gonna get dehydrated pretty quickly jumping around all over the place. And so, hopefully, that'll help you guys remember that when cells are placed into hypertonic environments, that will dehydrate the cells just like a hyper kid gets dehydrated pretty quickly. And so down below on the left hand side of our image, what we have are animal cells in different environments with different tonicity. And on the right, what we have are plant cells with the the same scenarios. And so starting with the animal cells on the left, when, again, cells are placed into hypotonic environments, they will swell up like a hippo. And so that's because all of the water is going to be flown into the cell, and so you can see the direction of these arrows down below are pointing into the cell because water will be flowing in. And again, that's because the environment is hypotonic and water always flows towards hypertonic solutions, and so the inside of the cell will be hypertonic. And, again, that could potentially cause some cells to lyse or rupture, so you can see that we have some cells lysing here. Now, when cells are placed into hypertonic solutions, again, the cells are going to dehydrate just like a hyperkid gets dehydrated, and that's because water is leaving the cell. So you can see the direction of these arrows is leaving the cells. And, again, that's because the inside of the cell would be hypotonic and the outside of the cell is hypertonic, just like we're indicating up above. And, of course, that could cause the cells to shrivel up and dehydrate and potentially die. So this is not a good environment. So, essentially, what we're saying is for animal cells, the hypotonic environment is not a good environment and the hypertonic environment is also not a good environment. And so for animal cells, it's the isotonic environment that is preferred, and that's because we have an equal, rate of water flow going into the cell and out of the cell. And so, again, isotonic environments preferred by animal cells. Now, over here on the right, again, we have plant cells. And we know that in hypotonic environments, cells are going to swell up like a hippo, and that's again because water is flowing into the cell just like what's being indicated. And so what you'll see is that when water is flowing into the cell here, it's actually not going to lyse because plant cells have cell walls and that prevents the membrane expansion. So here, what you'll see is that this hypotonic environment is actually preferred by the plant cells, And you'll see that the the central vacuole here is filled up with lots and lots of water and the cell membrane is pushed up against the inside of the cell wall and that creates a lot of turgor pressure which is helpful for the plant to maintain their structures. Now, over here with the isotonic environment, notice that, we have an equal water flow going in and out of the cell. And so, notice that the central vacuole is not as filled up as it is over here with the hypotonic environment. And also notice that we have these gaps here in between, the, cell membrane and the cell wall, and that is not a preferred scenario by, plant cells. So what we can do is we can place an x here to indicate that this is not really the ideal scenario for a plant cell. And then, of course, with hypertonic environments, cells are gonna dehydrate just like a kid gets dehydrated. And that's, again, because the direction of water flow is leaving the cell. And so notice how shriveled up this plant cell is, and that's because it's being dehydrated and this, again, is not gonna be a good environment for the plant cell. And so moving forward, we'll be able to get some practice utilizing these concepts. So I'll see you guys in those videos.
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Problem
Problem
What is the tonicity of the outside solution in comparison to the cell?
A
Hypotonic
B
Isotonic
C
Hypertonic
D
electrotonic
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Problem
Problem
What direction will the water flow?
A
Inside → Outside
B
Outside → Inside
C
Water flows in both directions.
D
No flow of water.
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Problem
Problem
Plants become turgor when placed in this type of solution: