Hello and welcome to another great lab with Professor Flores. In today's lab, we're going to go over diffusion, osmosis. We're also going to talk about membrane permeability and tonicity as well. Let's get started. Now, before we get started, we do need to master some terminology. And the first item that we're going to learn is what is a solute? Now a solute is any substance that dissolves in a liquid or a solution. A liquid and solution mean the same thing. Now an example of a solute is something like a salt like what what we see here labeled as number one. This can be a salt. This can be a sugar. Either would be called a solute. Now, a solvent is the liquid into which solutes dissolve into. For example, that could be water. In your lab, you're going to see that they actually define solvent as the following. A solvent is a liquid or a substance that there is most of. Okay. So once again in the lab they're going to define a solvent as the thing that there is most of and that thing that there is most of is that liquid which is water. Now in biology water is the universal solvent. Okay. And here we have it labeled as the number two. Now, a solution is the combination of a solute dissolved in a solvent. So, is the combination of a salt dissolved in water. That's a solution. In your lab, you're going to see that they call it a solution is a mixture of two substances with one dissolved in the other. Now, in your lab, they're also going to use another term known as media. A media is a substance through which diffusion occurs such as water and air. So water and air would be examples of media. You're going to see that they're going to use gels to as an example of media. Okay? So let me say that one more time. You're going to see in your lab that they're going to use things like gels as a media. Okay? A media. But just so you know, the media could be things like water and air, things that these molecules, these substances diffuse through. Okay, let's get going. Now, diffusion by definition is the random movement of molecules from an area of higher concentration to an area of lower concentration. And this diffusion, you've seen it before. You've seen it or you smelled it before. For example, when you walk to a room where maybe you you smell a funny odor, right? So, let's say somebody takes off their shoes and they just, you know, they're relaxing here in their living room. You're going to see that the odor that's coming off from the socks from the shoes will eventually fill the entire room. That is an example of diffusion. Another example would be cologne. Right? If we spray one side of the room with cologne, eventually that cologne, that smell will reach the other side of the room. And whenever you for example microwave popcorn, right, you will be able to smell that popcorn smell throughout the entire house, even if you're trying to hide it from someone. Now, this diffusion will occur until a uniform distribution of these molecules has been reached. Okay, here we also have an example what diffusion is. In diffusion, these molecules will move from a higher concentration, which we see on this side, to a lower concentration until a uniform distribution has been reached, until what we call equilibrium has been reached. Now, whenever we talk about diffusion, we do talk about concentration gradients. And you might be wondering well professor what is an example of a gradient. Now a gradient is present when there is a different concentration when there are different concentration of solutes in a solution. So what do we mean by that? Now here you can see that there is a we're adding a drop of water and here you can see that there is a concentration of that purple liquid right and there is a difference. So there is a lot of purple here where I'm circling and there is no purple here, no purple here and no purple here. So we say that we do have a concentration gradient. Okay. And eventually that molecule as you can see is actually diffusing out diffusing diffusing diffusing until we reach an equilibrium. Okay. So a concentration gradient is present when there are different concentration of solutes in a solution. So another example of a gradient that you see in everyday life would be for example when you travel down the road. And here we can see that we have a slope. Another name for a gradient is a slope. And mathematicians usually use the term gradient to describe a slope. Now for a biologist, we use the term gradient to describe again a difference in concentration. Now in today's lab, we're going to learn about how molecules diffuse and how fast they diffuse. And we call that the rate of diffusion. The rate of diffusion is going to describe how fast molecules like salts diffuse through uh liquid. And the rate of diffusion is actually influenced by different properties. One of them is known as concentration gradient which we just saw. So here's an example. So, if we add one drop here of this purple substance, this purple solute, you're going to see that if we only add one drop, it's going to take a long time for this molecule to diffuse. But if we actually start adding maybe uh 20 drops, okay, or maybe 50 drops, maybe a 100 drops, the more we add, the faster these molecules are going to diffuse and the faster these molecules will turn this water purple. Okay. Now another property that influences how fast these molecules diffuse the rate of diffusion is the density of the media. Density describes how thick that media is and media is referring to that liquid that the molecules are diffusing through. So another word for density is viscosity. So like the thickness of that liquid, the thickness of the water. Now here we can see that water doesn't have anything in here. So the density of the media here is very very low and molecules that we put in the water here are going to diffuse very very fast. Here you can see another media here which is a little bit thicker, a little more dense, a little more viscous. And here you can see that the water, the liquid is starting to become like a gel. So anything that we add in here in this purple substance is going to be diffusing a little more slowly. Now finally here we see another liquid which is very very dense, very very thick, very very viscous. Let me write the word viscous. Viscosity comes from the word viscosity. Viscous. Uh now since this item here that we see here is very very viscous, very very thick, the molecules, let's say we added sugar in there, those molecules would diffuse across that viscous media very very slowly. We would have to mix mix mix mix for a long time in order for us to really see that sugar fully distributed in that dense dense media. Now temperature also affects how fast these molecules diffuse across that substance that liquid. If the temperature is very hot like we see here, that sugar which would be a solute will diffuse in that liquid, the solvent very very very fast. In contrast, if we were to use a liquid that is very very cold, like we see in this right hand side, if we add a sugar to that container to that liquid, we would definitely see that it'll take longer for that sugar to diffuse across the entire liquid and we would actually have to mix a little more in order to speed up that process. So, temperature does influence the rate of diffusion as well. Another property that influences the rate of diffusion is the membrane permeability. So some membranes are going to have little pores that are going to allow molecules to go through that membrane. Okay? And if the pores are very small, the rate of diffusion will be very very low. But if we start making these pores bigger bigger okay the rate of diffusion will increase. So membrane permeability does affect how fast these molecules cross the membrane. Another thing that we're going to see another property that we see that influences the rate of diffusion is molecular size. And molecular size describes how heavy a molecule is. How heavy a molecule is. And in your lab, you will be looking at two molecules. Hydrochloric acid, which is heavier. Hydrochloric acid is heavier than ammonia, which is lighter. Okay, hydrochloric acid is actually more than two times heavier than ammonia. And we will see that the heavier molecules actually diffuse at a very very slow rate. Meaning that they are very very slow to move because they are heavier. It takes them longer to reach uh the entire container, the entire room because they are once again heavier. In contrast, ammonia, since it's a lighter molecule, it'll actually be able to diffuse across a container very, very easily and quickly. Now, the first lab activity that you're going to see in your lab will deal with molecular weight. And here you will see that a gas with greater molecular weight will have a slower rate of diffusion. So that is the goal of that lab to show you that the bigger the molecule, the greater the weight of that molecule, the slower it'll diffuse, a slower rate of diffusion. And we will predict that the cloud will form closer to the hydrochloric acid. And what do you mean by that, professor? What do you mean by predict that the cloud will form closer to the hydrochloric acid? Well, when we mix hydrochloric acid and ammonia, when you mix these two liquids, you actually form a little cloud, which we see here. Yes, a little cloud. And we're going to be looking at that cloud. And we're going to predict that the cloud is actually going to form closer to the hydrochloric acid because it's heavier. Okay, that's is that's going to be our prediction. And the reason why we're going to predict that is because the hydrochloric acid will not be able to for example meet exactly at the middle. It's not going to be able to emit at the middle because it's so heavy. So since it's very very heavy these molecules, so here you have a cotton ball which has been dipped in hydrochloric acid. This is what you're going to do in that activity. And these molecules are very very heavy. They're very, very heavy. So, they're only going to be moving a little bit. Now, on the other hand, the cotton ball here has what we call ammonia NH3. And since these molecules are very, very light, they're very light, they're actually going to be able to move across a tube faster. So when these two molecules combine, when these meet, they will actually start forming a a cloud. And that cloud is what we're going to be measuring. Okay? So we're going to place hydrochloric acid and ammonia on different cotton balls at at a specific distance. And then we were we are going to measure where the clouds form. Okay? So you're actually going to do this twice in this activity and then you're going to record your data. Okay? You're first going to do it for hydrochloric acid. And for example, you're going to measure from here all the way over here. And in your data, you're going to type in if it's exactly this, your data point is going to be 10 10. I believe this is in centimeters, but make sure you double check when you record your data. And then you're going to redo the whole thing. But in the other uh in the second time when you do that, you're going to have the hydrochloric acid on the right hand side and the ammonia on the left hand side. And then you're going to measure where the cloud will form. And you're going to see that it's going to form around this area. Now, for the next lab activity, you're going to be looking at how the number of the solute, the concentration affects the rate of diffusion. Okay? And you're going to be using a gel and crystals. Your crystals are going to be your solutes. Think about them as your salts. And the gel is going to be your semiolid. They call it a semiolid because it's not a full solid. It still is like a liquid, but it's not really a liquid at the same time. It's a semiolid. And the gel that you're going to be using is called the agar gel. Agar is just a specific type of gel that has many nutrients that allow us to grow different things in the lab. Just think about it as a gel that is not a fully complete solid that is still quite half. It's kind of like a hybrid between a liquid and a solid. So just think about it as a gel. And that's going to be your media. Your gel is going to be your media. And again, this gel is a semiolid, not completely solid. And your crystals are going to be your solutes. And these are going to be made out of potassium per manganate. Okay? You don't need to worry about the potassium permaganate. Just know that you're working with crystals and they will be your salts, your solutes. Now, for this lab activity, we're going to predict that the more crystals you have, the faster the rate of diffusion. So, the greater the concentration gradient of those crystals, the faster the rate of diffusion of those crystals. And we're going to place them at the center. We're going to place those crystals at the center. And then we're actually going to take a look at how much they travel from the center outwards. Okay, at 10 minutes, at 20 minutes, and at 30 minutes. I'll go over that again one more time in the next slide. Anyways, our strategy is going to be to place different concentrations of those crystals onto this gel into this semiolid media. Okay, a matrix is another word for media. Now you are going to be asked to do measurements and they're going to ask you to record your data in millimeters even though you're using a ruler that is in centimeters. So let me give you an example and let me give you uh the steps on how you need to calculate this. It's very easy. So for example here we have we look at our ruler. We place it here and we measure and we measure 4 cm. This ruler is in centimeters. And now we need to convert from centimeters to millimeters by using this converting factor which is 10 mm equals 1 cm. So pretty much this conversion factor is kind of like telling you, oh there's 12 inches in one foot. Oh, there is 60 minutes in 1 hour. Okay, the two values are identical. So 10 millimeters is 1 cm or there is 10 millimeters and 1 cm and we know that right. So from here to here that is 1 cm and we know that there are one two three four five 6 7 8 9 10 10 millimeters in 1 cm. So we know that this conversion factor is true. Now the way that you set this up for each of your calculations that you're going to do is as follow. You're going to write down 1.4 4 cm and you're going to multiply that by a fraction. All right? By a fraction. And then you're going to equal your fraction to what you want to get. What do we want to get? We want to get millimeters. Correct? So you set it up as you make it equal to millimeters. Now, you're going to have to put something here in the denominator, right? What are you going to put in the bottom part of your fraction? Okay. In the denominator. Yeah, you're going to put centimeters because you want to cancel out centimeters, right? And then that means that you're going to put millimeters at the very top. This is going to allow you to cancel the centimeters here. Okay. Now we simply use copy and paste. Okay, millimeters is 10 and centimeters is one. Okay, so we use copy and paste. And now we're able to do our calculation. We can cancel out these centimeters, right? And then we say 1.4 * 10, right? Because 10 / 1 is simply 10. So 1.4 four * 10, right? That is going to give us 14 millimeters. So, you can set this up for each and every one of your calculations or your measurements and you can just work this out on a separate piece of paper so you can record all your data. Or you can simply multiply your centimeters by 10 and you'll get millimeters. And that's what you're going to write down in your data. Now, for the next lab activity, we are going to observe diffusion across a selectively permeable membrane. And we're going to be taking a look at these molecules, including iodine, starch, and glucose. And we are going to create an artificial membrane, an artificial cell that has an artificial membrane. And this artificial membrane is going to be using what we call dialysis tubing. Dialysis tubing is a plastic that has microscopic pores, meaning microscopic little holes that will only allow very small molecules to cross the tubing. Now let's determine what can cross this tubing. Now what can cross this membrane? Only small molecules can actually diffuse across this membrane. Big molecules, something that is big will not be able to cross this membrane. It will not be able to cross the tubing. So anything that's too big will not be able to cross. Now let's determine what is a small molecule and what's a big molecule. Iodine is very very small as you can see here and since iodine is very small we will expect iodine to actually cross the tubing the dialysis tubing since glucose is also very small you can see here that it's made up of a single molecule glucose will be able to cross that dialysis tubing starch on the other hand is a huge molecule. It's actually made up of hundreds and hundreds and hundreds of glucose molecules chained together. So this starch molecule is actually hundreds of glucose molecules glued together and this makes it a really big molecule. So we don't expect starch to cross the dialysis tubing. Now before we actually do the activity, we need to understand how to test for starch, for the presence of starch and for the presence of glucose. So we're going to be doing two different tests. One of them will actually use iodine. So let's talk about iodine. Now iodine without the presence of starch will actually remain brown. Okay. So here there is no starch. No starch. So iodine is testing for starch. Okay. And when there is no starch, iodine will remain brown. However, when iodine meets with starch, when there is starch present, this iodine will actually turn into a purple color that you see here. Starch. Okay. Let me write down starch here for you. Okay. When starch is present, you will see that we get this dark purple color. And that is it. You just need to look at the color changes and that's how you'll determine whether or not starch is present. Now, to test for glucose, we are going to use glucose test strips. And whenever we dip these test strips into a liquid, after removing it from the liquid, after removing that test strip, that test strip will actually have a little box that will change in color. Now, if there is no glucose, then the color will be kind of like this aqua blue color after dipping it into that liquid. So if there's no glucose in that liquid, the test strip will be aqua blue. However, after dipping the test strip and the test strip turns into a brown color, then that tells us that yes, there is glucose in that liquid. And then we record uh yes or no for whether there is glucose or whether there is no glucose present. Now, we're going to predict that iodine and glucose will diffuse across the dialysis tubing because iodine and glucose are very, very small. They're small molecules. Very, very small. These two are small. Now starch since it's big we will also predict that starch will not diffuse because it's a bigger molecule has a bigger molecular size. Okay and this is going to be your setup as you can see here. Now for this experiment to work we do need to have a good strategy and the strategy is as follows. You are going to have a beaker and in that beaker you're going to place iodine and water in that beaker. And then you're going to get your dialysis tubing ready and you are going to add glucose and starch into the dialysis tubing. So you're going to have it outside like so. You're going to have it here. You're going to tie one end of the dialysis tubing and then you're going to add your starch and your glucose into that dialysis tubing. And once you do that, you are going to then kind of like tie off the other end. Let me show you real quick. So now you that you have starch and glucose in here, you're simply going to tie this other side right here. Okay? So we're tying it up. And then you are going to put that dialysis tubing into that beaker. And this is how it looks like now. Then you're going to wait for 10 minutes. And then you're going to record your data. You're going to record your data at time zero. So, as soon as the timer starts and after 10 minutes, okay? And after that, we're going to be looking at the color changes to determine whether or not diffusion occurred. So, once again, follow the steps on the right hand side to create an artificial cell using the dialysis tubing. And again, your dialysis tubing will be tied off at this end right here, right? And then you can see this kind of like other side of the plastic. And then you're going to introduce your starch and your glucose into there. And after that, you're going to tie this off right here. Right? You're going to tie it off and you're going to end up with this tootsie like artificial cell. And after that, you're going to put it in into the beaker as you can see here. So, the beaker is going to have this pouch of dialysis tubing. And whenever they say, "Hey, um, membrane this or artificial membrane that," they're referring to the dialysis tubing. The diialysis tubing is our artificial membrane. And this membrane is semi-permeable. Again, it has microscopic pores that will only allow small molecules to cross. Inside of that little pouch, you will have starch and glucose. Remember, glucose is small and starch is big, right? And in your beaker, you're going to have iodine and water. Remember, we're looking at the movement of iodine only here. And you know that iodine is very, very small. So you should predict that iodine will go inside right it because it it is small. So it will cross that membrane that dialysis tubing membrane and glucose is very very small. So if glucose is inside, if glucose is inside and it's very very small, you should also predict that glucose will also cross that membrane into the beaker. All right, starch is too big. I'm going to put a letter S here for starch. Starch is too big. So it cannot cross this membrane. It cannot cross the membrane, right? Because it's too big. So it'll be trapped inside of the dialysis tubing. Now you will get to this question and the reason why I do have the answers for this question is because the answer choices that are correct might be a little confusing. So I want to go over them so you don't confuse yourself. Now so the answer here include A and B. Let's read the question. How are you going to determine if iodine and starch and or starch diffuse across the dialysis tubing? Okay, so they're trying to uh remind us like, hey, remember that when iodine, okay, meets starch, what color do you get? You get a dark purple. Dark purple. They're trying to remind you here, hey, don't forget that iodide will only test for starch. So, here we're only looking for starch. We don't care about glucose right now. Um, remember when iodine is alone, when it doesn't have starch present, it'll look brown. But when iodine meets with starch, we get this dark purple color. So let's take a look at option A and understand why it's correct. If both iodine and starch are able to diffuse across the membrane, both the dialysis tubing and the beaker will look dark purple. So they're saying that if starch is able to diffuse into the beaker side where you have iodine now you're going to have iodine and starch out here. Yes, that will look dark purple. That will actually make the beaker look dark purple. Okay. Now if is is this really going to happen? No. Remember starch is too big and it cannot cross the membrane. But yes, this is a correct assumption. Again, they're trying to remind you iodine plus starch will give you a dark purple. Okay. Now, the next option is asking us, hey, letter B, letter B. If only iodine is able to diffuse across the membrane, the solution in the dialysis tubing bag will look dark purple. So let me uh clear that up for you. So now they are telling us well on the other hand what if iodine is able to make it into the tubing into the cell. Okay. Now this side will actually look purple. Okay. And this is actually what we expect because we know that iodine is a very small molecule and iodine will be able to go into the dialysis tubing. So we should be able to get a tubing bag, a dialysis tubing bag that looks dark purple. Okay. So that should be correct. That is actually another correct assumption. And this is actually what we are expecting to see because starch is remember too big and it cannot leave the dialysis tubing. Now the last option is actually incorrect because they're telling us if only starch is able to diffuse across the membrane the solution in the dialysis tubing will look dark purple. Okay, let's try to understand what they're trying to tell us here. Now, let me underline key words here. If only starch is able to diffuse across the membrane, the solution in the dialysis tubing will look dark purple. So, they're telling us here then if starch is able to go into the beaker because they're telling us that it'll diffuse across the membrane, right? And they're tell they're not telling us that iodine is going in here. They're they're assuming that it's not going into the dialysis tubing, right? Because they're saying only starch only starch is diffusing across the membrane. So we can safely assume that they're saying iodine is not going into the dialysis tubing. If iodine does not go into dial the dialysis tubing then there will be no color change because the starch by itself will not change in color. Okay. So if the starch if only the starch is able to diffuse across the membrane the solution in the dialysis tubing will not will not look dark purple again because if you don't have iodine mixed with starch you don't get a color change. All right I hope this makes a little more sense. Again, the takeaway of this question is to remind you iodine plus the presence of starch will give you a dark purple. And just make sure you don't get confused. Starch will not be able to cross the membrane because it's too big. But in the options here, they're assuming that starch does cross the membrane. Now here we're going to write our data, our observations for the movement of the molecules that we're working with. And those molecules include glucose. So glucose, starch, and iodine. Okay? So remember when we started, we started by adding glucose into the tubing. So I'm going to write down glue for glucose, right? and starch, a big letter S for starch. And we added iodine in the beaker. All right, so let's write down the correct option for each of these options. So let's go over the first one. Did we have glucose in the tubing before diffusion when you started? Yes, that is correct. We see glucose in the tubing. Did you have glucose in the beaker? No, we only have iodine. Next, starch. Did we start off with starch in the tubing? Yes, we did. Did we have starch in the beaker? No, we only had iodine. Now, for iodine, did you have iodine in the tubing? No, of course not. We only added iodine to the beaker. Okay, well done. So, this makes sense, correct? Yeah, it should. All right, let's move on to the next one here. Now, after the 10 minutes, you're going to see that there was a color change in this small little dialysis tubing. So, I'm just going to write down glucose because I know that we started off with glucose here and starch. Okay. And here we have iodine still. Now, let's take a look at uh what's happening here. Now, the tubing actually became dark purple. Why do you think it became dark purple? That's right. It became dark purple because this starch probably got mixed with iodine. Iodine went into the dialysis tubing. And now, what about glucose? Did glucose move? Well, yes. It looks like glucose actually tested positive. Okay. In the beaker. So now we actually see some glucose in here. Okay. Now with that being said, let's record our data here. Now for the glucose in the tubing, we should still have glucose in the tubing. Yes. Now do we see glucose in the beaker? Well, according to this glucose test, yes, there is glucose in the beaker. So, we saw that glucose diffused across the membrane. What about starch? Is starch found in the tubing? Yes, we see that starch is present. And do we see any starch in the beaker? The beaker, notice that it's still brown. It's not dark purple. So that means that iodine has not mixed with starch in the beaker. So the answer should be no. Now let's take a look at iodine. Did iodine move into the tubing? Yes, of course. That's why we see that it became that per dark purple. That's why we see that that dialysis tubing became dark purple because iodine went into the dialysis tubing to mix with the starch. Is iodine still present in the beaker? Yes, of course. The beaker is still dark. Not dark, but brown. Brown. Okay, I hope the answers made a little more sense. Let's move on to the next slide. Now, they're going to ask us, did diffusion across the membrane occur for the glucose solution? So, how did we test for glucose? Remember, you started with glucose in the baggie and we want to know if glucose actually went into the the beaker. Okay. And how do we know how do we test for this? Well, we use a glucose dipstick, a glucose strip. And when we dipped it before, before before we saw that when we dipped the strip in the beaker in here and we took it out, we saw that it gave us a negative result. So there was no glucose before the fusion, but after 10 minutes after we dipped it in here, we saw that the glucose test strip actually turned brown and brown in this case according to this scale this color scale tells us that glucose is present. So we did see that glucose according to these results the answer is yes glucose did move across the membrane diffusion did occur for glucose and it happened because glucose is such a small molecule. Now next they're going to ask us about the diffusion for starch. The diffusion across the membrane occur for starch. So one thing that I want to remind you is that starch is a big molecule. So starch is a big molecule and it cannot leave that membrane. Now so the answer should be no. Okay. Did diffusion across the membrane occur for starch? No. How do we know that? Well, because starch never actually made it into the beaker. And we know that starch never make made it into the beaker because the beaker which contained iodine never turned dark purple right. However, the starch since it remained in the tubing right in the diialysis tubing did turn dark purple. It did turn dark purple and that's because iodine is way smaller and iodine was able to cross the membrane. So the starch and the iodine once they meet they actually create this dark purple color that you see right here. Okay. So the answer for the question is no. Starch did not diffuse across the membrane. starch was trapped in the dialysis tubing and since iodine is very small iodine did cross the membrane did diffuse and mix with that starch and that allows us to see that color change but again the answer for starch is no dial the diialysis tubing will not allow starch to diffuse across because starch is too big. So in conclusion, diffusion occurred based on molecular size. Iodine and glucose are very very small. These are much smaller molecules than starch which is very very very big. Starch is big and therefore only iodine and glucose were able to diffuse across the dialysis tubing. Now the last concept that we're going to explore is osmosis. And osmosis is actually the movement of water, not the movement of salts. The movement of water across a membrane that is selectively permeable for water. So we call that a selectively permeable membrane. And in this case, the membrane will only allow water to move, not the salts. Okay. Now, one way that I remember osmosis is by remembering this simple statement which says salts suck. What does that mean? It means that water will go wherever it is saltier because salts suck. So, let's take a look at this before and after beaker. So, on the left hand side you see the before before osmosis. On the right hand side, you're going to see after osmosis. And here we're taking a look at a semi-permeable membrane that only allows water to go through it. And the salts, which are the spheres, are not going to be able to cross the membrane. Okay. So, let's take a look at on the left hand side. On the left hand side, we see that there is a membrane. And now we see that there are way more salts on this side right here. Right? So if you remember, okay, salts suck. How is water going to move? Is water going to go in this direction or is water going to go in this direction? Okay, if you said in the second direction, right, you are correct. Water will actually go in this direction because it is saltier. Okay? And remember salts suck. Water will always go wherever it is saltier. And for this reason after let's say 30 minutes, right? You will actually see this in this beaker. Okay. Now we have an even distribution of water in both con in both sides of the container and that makes each side uh to have the same concentration of salts in water. Okay, again here we're only looking at the movement of water. The salts are not moving. So therefore, water had to go in this direction in order to have the same amount of salt concentration on both sides. Now what about tonicity? We actually use the word tonicity whenever we talk about osmosis. And tonicity is the ability of an extracellular solution to make water move into or out of a cell via osmosis. Now the word extracellular is very important and it's also very simple. Extracellular refers to the environment outside of the cell membrane. Extracellular means the outside of a cell membrane. The outside of a cell. And therefore these solutions that we're talking about are always going to be the ones outside of the cell. We can only change the tonicity of the extracellular environment. Okay. Now moving on from here, remember salt suck. Water will go wherever it is saltier. Okay. Water will be sucked to the saltier side. Now whenever we describe tonicity we do talk about three different types of tonicities. Isotonic, hypertonic and hypotonic. Isotonic describes a concentration of the extracellular solute being equal to the concentration inside of the cell. What do we mean by that? Well, we are saying that the salts in the water in the extracellular solution are have the same concentration as the salts inside of the cell. So, let's work with a value. Let's say 300. Let's say that the value of salts of the red blood cell is 300, which is true. This value is actually called osmolarity. But for the purposes of our class, we're just going to say that it's 300 and 300 and that's all. So let's say that the red blood cell has a value of 300 salts inside of it and the extracellular solution has a value of 300 as well. 300 salts in that solution. These two values are identical. This means that the liquid the saltiness of the extracellular environment has the same saltiness as the salts or the water solution inside of the red blood cell. So what happens is that water goes in at the same rate as it goes out of this cell. So therefore the shape of the cell stays the same. It stays normal. Now in a hypertonic solution we're saying that the concentration of the extracellular solute is greater to the concentration inside of a cell. So here we have hypertonic solution. And again we're saying that the solution the liquid outside of a cell is saltier. Hyper means more, right? Like when you give candy to a child, they get a lot of energy. So hyper means a lot of. So if the value of the inside of the red blood cell is 300, then the value of the outside could be something way bigger than that. Let's say 500, right? 500 is way more than 300. So now we're talking about a hypertonic solution. And if you recall osmosis, osmosis tells us that salts suck, right? So what's going to happen then is that the salt is going to go where there is more salt and there is more salt in the outside. And for this reason, what happens is that the cell starts to shrink. Okay? Or the cells starts to cremate. Okay? Cremate means to shrink and shrivel up. On the other hand, when we're talking about a hypotonic solution, hypo means less than. So here we're talking about a concentration of extracellular solute that is lower to the concentration inside of the cell. So if the cell has a concentration of 300, a saltiness of 300, then the outside will have a concentration of what? Something less than 300. What would be the extreme number? What is the least of 300 or what is the least number the lowest value when comparing to 300? Right? You could have said 100 or you could have also said zero. Correct? Zero. Now whenever we actually use for example pure water, if you were to inject someone with pure water, what would happen is osmosis salts suck. Where is it saltier now? Outside or inside? It is saltier now inside. So what happens then is that all that water is going to start going where it's saltier because of osmosis. Because salts suck. See, like you see there, there you go. And what will end up happening to your red blood cells is that the cells will begin to swell and eventually they will burst. Another way of saying to burst is lic. Lis means to burst. And if you're a plant cell, what will happen is that the cell will actually get bigger. it will not burst because they are protected by a cell wall. But our red blood cells, animal cells are usually not going to have a cell wall. So what will happen in this case? If you put a a red blood cell in diluted water or distilled water that does not have any salts, the cell will swell and eventually it'll burst. Now, let's put the three different tonicities side to side and let's compare them. Okay, let's talk about them. Now, in each one of these beers, we're going to have a red blood cell and that red blood cell will have a saltiness of 300. That value is not going to change. Remember, tonicity does not describe the inside of a cell. It describes the outside of a cell. Okay. All right. So, there you go. And just assume that these are perfect circles. Okay. 300 for each. Now, let me fix that last one. All right. There you go. They all have a value of 300, a saltiness of 300 inside of them. Now the only thing that we're going to change then is the tonicity. So let's add an isotonic solution to the first beaker and then we're going to determine what the cell shape will be. Now an isotonic fluid iso means the same an isotonic solution then will have the same saltiness as the inside which is 300 in this case. And what's going to end up happening then is that water, the same amount of water that goes inside will also leave the cell. You see that? So the net movement of water will essentially be zero. There's going to be no net movement. The total movement of water is going to be zero. That's what we're trying to say here. and the cell shape will continue to be normal. Okay? All right. That's what's going to happen in an isotonic solution. Now, let's go on to the next example. Now, in the next example, we're going to add our hypertonic solution. And hyper means more. So, what is a number more than 300? All right, we can use 500. That's correct. or we can use 1,000, right? Let's stick with 500. Okay, so you could have used 500, 600, anything bigger than 300. And now remember osmosis salts suck. Where is it saltier? Is 300 saltier or 500 saltier? That's right. 500 is saltier. So since salts suck, water is going to go where it's saltier outside. And if the volume of water keeps on going out, what do you think is going to happen to the cell? Is the cell going to stay normal? No, I don't think so. Right. Is the cell going to get bigger and burst? No. Is the cell going to shrink and creatate? Yes, that is correct. So a cell is going to creatate whenever it's placed in a saltier solution in a hypertonic environment. All right, moving on to our third example here. So here we're going to create a hypotonic solution. So we're going to put our red blood cell in a hypotonic solution. And anything lower than 300 is hypotonic. 200 is hypotonic, 100 is hypotonic or even zero is hypotonic. Let's stick with zero. So here we have our value zero. Okay. Now if you remember osmosis if you forget everything just remember salts suck. Okay. Where is it saltier inside or outside? It is saltier inside of the red blood cell. So water is going to start going into the red blood cell. Into the red blood cell. You see that? Because it's saltier inside and salt suck. That is osmosis. Now what's going to happen to the shape of the red blood cell? Is it going to stay normal? No, I don't think so. Is it going to get bigger? Is it going to start swelling? and then eventually bursting. That sounds about right. Do you think is it is it going to create? Is it going to shrivel up? No, I don't think so. It's gaining water. So, the correct answer is that it'll burst. Yes. Whenever we put our red blood cells in a hypotonic solution, they will burst. So for that reason whenever we go to the hospital and they give us intravenous fluids that intravenous fluid will have a specific amount of salt that is isotonic to your bloodstream so that your blood cells don't burst. Now in your lab activity, you're first going to take a look at the Elodia cells. And these are simply plant cells. Okay? Plant cells. Elodia is a plant. So here we're looking at plant cells. And this is how they look like in isotonic solution. Now we're going to actually observe the effects of two different tonicities on the plant cells. And one tonicity will be hypotonic and it'll be hypotonic when we're using distilled water which is pure water without salt. Okay. The other solution is going to be hypertonic and a hypertonic solution will actually have salt and it's going to be that salt water which will actually be 10% salt. 10% salt is quite salty. And the terms NAC are read or pronounced sodium chloride. Sodium chloride is a fancy way of saying salt. Okay? So, whenever I say salt, we're just saying sodium chloride. And what's going to happen here is that since these plant cells have a rigid cell wall, they have a cell wall. And you can see that cell wall right here. I'm highlighting it as we go. Okay, that rigid cell wall helps them keep their shape, that cell shape even when water moves into or out of these cells. Okay. So, you're going to see that water will actually move in and out of the plant cells. However, you're going to still see that skeleton, that cell wall that helps these plant cells keep their shape. Now, in your lab activity, you're going to see a slightly different definition, and I do want to go over these definitions so that you get a better understanding. To me, they're a little confusing, but let's make sense out of them. Okay, so tonicity. Tonicity is the ability of a solution to change volume of a cell through osmosis. So, it's pretty much reminding us tonicity is the ability of a solution to move water through a cell. And by moving water through a cell, we change the volume of that cell, the amount of water in that cell. A hypertonic solution, hyper means more than, is a solution with higher concentration of non-permeable solutes in comparison to another solution. And remember that solution is extracellular. Okay. So whenever we are describing the tonicity, we're always describing the tonicity. We're always describing the liquid outside of a cell. Extracellular. And non-permeable refers to something that cannot cross a membrane like salt. salt cannot cross the membrane because it's actually a charge of the molecule that cannot cross the membrane. Hypotonic solution is a solution with a lower concentration of non-permeable solutes in comparison to another solution. So a hypotonic solution is simply a solution that has less salts and a isotonic solution iso means the same. So this is a solution with the same concentration of salts or non-permeable solutes in comparison to another solution. Now we're going to predict in this activity that the elodia cells placed in hypertonic solution will actually shrink hypertonic solution. Okay. And that's because osmosis will draw the water out of the cells. causing the cell to decrease in volume. So let's get to this experiment here. Let's let's actually get a visual here. So hyper means more than. So I'm going draw in my water solution and then I'm going to draw in my plant cell. And just to keep it consistent, I'm going to use the same value, which is 300. Okay? And in your lab, they're not going to use any values, but it's always good to remember that the saltiness of the cell, the inside will not change. So, it's going to be 300. 300 for the purposes of our class. Now the outside solution then if we're talking about a hypertonic solution it has to be greater than that. So let's say it's 10,000. Okay 10,000 and I'm using 10,000 as a random example but that's going to help you remember that 10%. Okay? So it's 10,000 anyway. So where is it saltier now? Inside or outside? It's saltier outside because we're using a very salty liquid, right? So, what's going to happen then is that the water of the plant cell will start to leave and what will happen then to the plant cell is that the plant cell will actually start to get smaller. It'll shrink and it'll decrease in volume. That's our prediction. Now our strategy will be to place the Elodia plant cells, these little Elodia leaves in solutions with different tonicities. We're going to use distilled water. That's going to be our hypotonic solution and we're going to use 10% sodium chloride, which is going to be our hypertonic solution. After that, we're going to examine the appearance of these cells, the shape of the cells under the microscope to see if the cells actually changed in shape. Now, when you're doing your lab, you will have to determine the tonicity of the environment that the cells are in and also the cell shape. Okay? The appearance of the cell. So in the top picture here we can see that the cells are actually in a hypotonic solution because water is actually going into the cells. And on the second environment here you can actually see that the water is actually leaving the cells because they have been placed in a hypertonic solution. When you are recording your data, they will also ask you to record your picture. And you're actually going to click on this little button here to save your picture into your data. The conclusion will be to understand that salts suck and they also cause water to move which is a process known as osmosis. So the entire reason why we're doing this lab is to understand osmosis and to understand that a hypertonic solution will cause water to leave a cell because salts suck. And if we put the cell in a very very very hypertonic solution that has a lot of salts, the water will go where it's saltier. So water will leave the cell. In contrast, when you put the wa your cell when when you put your cells in a hypotonic solution. In a hypotonic solution that does not have any salts, well, now the salts are only found inside of the cell. And since salts suck, water will enter the cell. Okay, remember salts suck. Water go water goes where it is saltier. Now for the last activity you will observe the effects of different tonicities on red blood cells. Okay. And the three different tonicities are as follows. The hypertonic solution that is 10% sodium chloride is going to be saltier than the inside of a cell. The inside of a cell is going to have a tonicity or saltiness of 0 9% NaCCl salt. So your blood actually has a 0.9% salt concentration. And since we need an isotonic solution, we're actually going to use a solution of 0.9% sodium chloride. Now, the hypotonic solution that you're going to be testing is going to be 0% salt. 0% salt is pretty much pure water, which in this case they call it distilled water. You will also need to record the cell transparency and there's going to be two options only. Is it cloudy or is it transparent? So for example, this test tube here is cloudy. This test tube is also cloudy. And this test tube is transparent. You will also need to record the shape of the cell, the cell appearance. Okay. And for example, here we can see that the cells are created. They're starting to shrivel up. Created. In this example here, we can actually see that the cells are actually normal. Normal. And in this example here, you don't see anything. And that means that the cells have actually burst. By looking at these cells, you should be able to determine the tonicity and you're also going to be asked to save your current microscopic image when you're recording your data. The conclusion of this activity will be to understand that once again salts suck and cause water to move pretty much osmosis. We need to understand osmosis. That's the whole purpose of this activity. And we need to understand that hypertonic solutions cause water to leave the cells. A hypertonic solution means that the liquid outside of the cell is saltier. So salt suck. The water is going to leave the cell and go where it's saltier. Isotonic solutions. We also need to know that isotonic solutions cause no net movement of water. Because if the two values of salt environment are the same inside and out of outside the cell, the same water that goes into the cell will also leave the cell. So there will be no net movement of water in isotonic solutions. Another reason why we're doing this lab is to understand that hypotonic solutions hypo cause the cells to burst and that causes the cells to disappear as they no longer block light passing through the blood as we see in this picture here. Okay. Why do the cells burst? Well, because if you put the cells in pure water, now the only place where you find salts is going to be inside of the red blood cell. So, all that water will then start to go into the red blood cell causing the red blood cells to burst. Finally, we also need to understand that cells are able to exchange water because the cells have selected permeable membranes. So, meaning that the cells have a membrane that is able to only allow water to move. Okay? And that membrane prevents things like sodium chloride, NaCCl from penetrating that membrane. So we call these molecules non-penetrating molecules and these will not move across that membrane. So once again, water is able to move across a membrane because the membrane of your red blood cells or the membrane of your cells is selectively permeable. All right, I hope you enjoyed this video. I know it took a little longer than expected, but I hope it helps you complete the activities for this week's lab. All right, if you have any questions, feel free to message me. Have a good one.