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Main content
Current time:0:00Total duration:6:30
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Video transcript

so I have three different scenarios here of a cell being immersed in a solution in the cell is this magenta circle that's the cellular membrane and then I have the water molecules depicted by these blue circles and then I have the solute inside of the solution inside of the water solution that we depict with these yellow circles and I've clearly exaggerated the size of the water molecules and the solid the solute particles relative to the size of the cell but I did that so that we can visualize what's actually going on now we're going to assume that the cellular membrane this phospholipid bilayer is semipermeable that it will allow water molecules to pass in and out so a water molecule could go from the inside to the outside or from the outside to the inside but we're going to assume that it does not allow the passage of the solute particles so that's why it's semipermeable it's permeable to certain things or we could say selectively permeable now what do we think is going to happen well the first thing that you might observe is we have a lower concentration of solute on the outside than we have on the inside so in any given moment of time you will have some water molecules moving in just the right direction to go from the outside to the inside and you will also have some water molecules that might be in just the right place to go from the inside to the outside but what's more likely to happen and what's going to happen more over a certain period of time well the water molecules that are on the outside we talked about this in the osmosis video they're going to be less obstructed by solid particles if they happen to be if this ones happens to be moving in that direction well it's going to be it's going to make its way to the membrane and then maybe get through the membrane while something may be this if this water molecule was moving in this direction well gee it's going to be obstructed now maybe this is bouncing back and it's going to ricochet off of it so the water molecules on the inside are more obstructed they're less likely to be able to fully interact with the membrane or move in the right directions they're being obstructed by these solid particles so even though you're going to have water molecules going back and forth and a given in a given period of time you have a higher probability of more going in than going out and so you're going to have a net inflow net inflow inflow of h2o of water MA Jules now situation like this where we're talking about a cell and it's in a solution that has a lower concentration of solute it's important that we're talking about a solute that is not permeable that is that is not allowed to go to the membrane the membrane is not permeable to that solute we call this type of situation this type of solution that the cell is immersed in we call this a hypotonic solution hypo tonic hypotonic solution and anytime we're talking about hypotonic or as we'll see isotonic and hypertonic we're talking about relative we're talking about relative concentrations of solute that cannot get through some type of that cannot get through some type of a membrane and the word hypo you might have seen it in other things it's a prefix that means less of something so in this case we have a lower concentration of solute in the solution then we have inside of the cell and because of that you're going to have osmosis you're going to have water molecules going from the inside you're going to have water molecules going from the outside I should say to the inside and that's actually going to put pressure on the cell the cell itself might might expand or it could even if there's enough pressure it might even it might even explode so now let's go to the next scenario in this scenario we have roughly equal concentrations of solute on the outside and on the inside at least I tried to draw them that way so in this situation the probability of a water molecule in a given period of time going from the outside to the inside or from the inside to the outside is going to be the same and so you're not going to have any net inflow or net outflow you're always going to have water molecules going back and forth but there's not going to be any net inflow or outflow and so in this situation so let's see let me write no net no net flow and this type of solution where you have the same concentration of solute in the solution as you do inside the cell we would call this an isotonic this is an isotonic solution I so tonic solution and the prefix I so you refers to things that are the same it has the same concentration of solute and so you have no net inflow so hypotonic solution you have water molecules going into the cell the CEL expanding kind of like a filling balloon isotonic solution no net flow and of course you could imagine in this last scenario I have a higher concentration of solute on the outside than I have on the inside and we can guess what's going to happen so first what would I call this well I have more of something on the in the solution so I would use the prefix hyper I have more of it more hyper tonic this is a hypertonic solution and once again the water model the solid can't go can't go across the membrane but the water molecules can and you're going to have water molecules going from the outside going from the outside to the inside and from the inside to the outside but the probability that the ones going from the the one so on the inside are going to be less obstructed to get go out than the ones on the outside to go in and so you're going to have a net outflow you have a higher probability of things going from the inside to the outside then you do from things going from the outside to the inside because they're going to be more obstructed and so they're going to be held back I guess in different ways so in this situation you're going to have you're going to have two water escape the cell and the cell actually might shrivel up the cell since it's going to lose that pressure from the water the cell itself might shrivel up in some way and you could actually see this in actual living systems if you were to put a red blood cell into a hypotonic solution the water is going to rush into it and it's going to look it's going to blow up it's going to it's going to expand and so it's going to look like a overinflated red blood cell and an isotonic solution it's going to look the way that we're used to seeing a red blood cell actually having kind of that little divot in in the in the in the middle area while over here it's all going to expand and then in the hypertonic solution the water is going to escape the red blood cell and then you would actually see it kind of shrivel up shrivel up a little bit like this because all of that water is Li or or we have a net outflow of water molecules
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