Transcription
Okay, so in this video, we're going to talk about how solute concentration affects the movement of water across a membrane. And this is basically the definition of osmosis.
Okay, um, so I'm gonna use these slides here. All right, so here's, um, we're gonna follow along with this example. I've got three test tubes here. Uh, in the first test tube, we're gonna put a cell, an animal cell. It could be a human cell. And, uh, the solute concentration inside this cell is 0.9 percent solutes. There could be all kinds of solutes in there: proteins, salts, DNA, sucrose, glucose, sugars, carbs, all those solutes all added up together, total 0.9 percent. All right, and this cell is bathing in a solution in the, um, test tube that is also 0.9 percent. And that's what that env, env stands for, the environment. So the environment outside the cell, all that liquid that the cell is floating around in, is also 0.9 percent solutes. So the cell is 0.9, the outside solution is 0.9 percent. And in this diagram, or in all these diagrams, those blue arrows represent water moving into and out of the cell. And in this diagram, there are two arrows going into the cell, showing that some water is coming in, and there's exactly the same amount of arrows going out of the cell, meaning that the same amount of water is going out. So there's overall some water coming in, somewhat going out, and it's evenly balanced. And the cell is just hanging out there. And we have a sentence that we can use to describe this situation. And this is what we say: "The environment, so the outside liquid, is isotonic compared to the cell." All right, so, uh, that means, uh, isotonic means the same concentration. It's a fancy word. Iso means the same, and tonic means concentration. So I could say, "The environment is the same concentration as the cell," or I could be fancy and say, "The environment is isotonic compared to the cell." So that's our first example. And in this situation, water, there's no overall movement of water. It's completely evenly balanced. All right, so let's move on to our next diagram. We're going to take another cell, which is going to be 0.9 percent solute. So this is starting off, the cell is the same 0.9 percent. And we're going to put it in an environment that is greater than 0.9. So let's say this environment is like, uh, 2 percent. So it's a higher concentration than the cell. So in this example, you can see that there are definitely more blue arrows exiting the cell. Water is going out of that cell, and hardly any is coming in. Way more is coming out than is going in. And you can see the cell has shrunk up. All right, this is, this is, uh, demonstrating the process of osmosis, where water moves across a membrane to where there are more solutes. The solutes can't move. The solutes can't get in. The solutes from the outside can't get in, and the solutes from inside the cell can't get out. The membrane doesn't allow that kind of movement, but water can move. And so, and the water will always move in the direction of where there are more solutes. And seeing, and as in this example, there's more solutes on the outside, the water is going to exit the cell and go to the outside environment. And the sentence that we use here is that "The environment, so the outside solution, is hypertonic compared to the cell." Hyper means more or extra, like hyperactive, extra active. So hypertonic literally means more concentrated than. So we could say, "The environment is more concentrated than the cell," or we can say, "The environment is hypertonic compared to the cell."
So then, let's move on to the very last example here. We're going to take another cell, 0.9 solutes again. And this time, we're going to dump it in a test tube that has an environment that is less than 0.9. So this environment, maybe it's 0.1 percent. So it's got less solutes floating around in this test tube than there are floating around inside the cell. Now, remember, the solutes again can't get in, the solutes can't get out. They're stuck wherever they are. But the thing that can move here across a membrane is water. And water is going to go to where there are more solutes. And according to this, if the cell is 0.9 and the outside is 0.1, there are more solutes inside the cell. So in this example, water is going to move from the environment into the cell. And you can see what's happened to it. So here you can see three arrows go, three blue arrows going into the cell, and only one blue arrow coming out, which means more water is going in than is coming out. And eventually, the cell's gonna blow up, blah, blah, blah, like an overinflated balloon, until eventually, if it's an animal cell, it's just gonna burst, which is what's happened to this. Not a good situation. So, um, we have a sentence for this. And that is, we say that "The environment, the outside solution, is hypotonic compared to the cell." Hypo means less or under or fewer. Hypo. So, uh, this sentence is saying, "The environment is less concentrated, hypotonic compared to the cell." The environment is 0.1, the cell is 0.9. All right, so those, let's have another look at those terms real quickly, uh, just written down here. So iso means the same. Isotonic means the same concentration. And you can think of for chemistry, isomer, isotope, iso, isometric, this all means the same. Hyper means more. Hyperactive, hyper vigilant, hyper. So hypertonic means more concentrated. And then hypo means less than. So hypoallergenic means less, less allergy causing. Hypothermia means your temperature is under, it's less than what it should be. Or even hypodermic needles, they go under the skin, under the dermis, hypodermic. So, um, these, these words should be kind of rememberable if you remember the patterns here, iso, hyper, and hypo.
So let's have one last look at how we use them. A couple of looks here. So, um, these words have to be used in a sentence to compare things. So they're like, they're a comparative adjective, basically. So it's like saying the word shorter. If I just say, "Rachel is shorter," it doesn't really help me with any kind of information. It doesn't tell me, is Rachel shorter than Shaquille O'Neal? Is Rachel shorter than Sarah? Is Rachel shorter than last week? You have to have a "than" to compare, compared to. "Rachel is shorter compared to Shaquille O'Neal." "Rachel is shorter compared to 10 years ago," whatever. So you can't just say, "A cell is hypotonic," period. That's like saying, "Rachel is shorter." It doesn't help us. You've got to compare it to something else. So you can say, "A cell is hypotonic compared to the outside environment." That you always have to have that "compared to" for it to really make sense. One other thing, and this drives me kind of crazy, is that, uh, these words can be used in, um, you can use the same word, hypotonic and hypertonic, sorry, you can use different words, hypotonic and hypertonic, to describe the same diagram. So what happens a lot, I see on, on, um, I see on exams is that students will, um, look at, so I get the latest pointer, will look at, uh, this, um, excuse me, this, this picture, uh, down here in the corner where it says the cell is 0.9, the environment is 0.2, and they'll say, "Oh, that picture is the hypertonic picture," or "That picture is the hypotonic picture." And that, that is not correct. This, this picture is not hypotonic or hypertonic. It is actually both at the same time. And you're like, "How can it be both?" Well, let's look at the example up here with Miley Cyrus and Liam Hemsworth. Okay, so we have some words that are the mean opposite, shorter and taller. And I can use both of those words to describe this picture. I can say that, "Miley is shorter than Liam," or I could say, "Liam is taller than Miley." And that's the same information, just depends on who I start the sentence with, whether I get to pick shorter or taller. All right, so using that logic, we can, um, use that to describe our example down here. I'm going to move my video picture out of the way because I realize that you can't see, uh, what I'm doing here. So hold on. If I move myself up here, okay. So if we, uh, look at this picture here, um, the cell is 0.9 and the environment is 0.2. The cell has more solutes than the environment. So we can say, "The cell is more concentrated, hypertonic compared to its environment." But if we flip that around and start the sentence with the environment, we can also say that, "The environment is less concentrated, hypotonic compared to the cell." So this picture, this test tube and the cell that's exploding, we can use the word hypertonic to describe this, this scenario, and we can use the word hypotonic. It just depends which way around you write the sentence, just like the shorter and taller example. So don't fall into the into the trap of saying, "Oh, that diagram is hypertonic," because it's also hypotonic, depending on which viewpoint you're looking at it from.
All right, so, um, as a little finishing up here, here are some, uh, practice problems showing three different plant cells. So on these plant cells, you, the blue arrows are showing water movement, once again. And so by looking at which way the water's moving in these three examples, see if you can write down on a piece of paper or figure out in your head what sentences you would say to describe these examples: "The cell is hypo, hyper, or isotonic compared to the environment," because water is going whichever direction. See if you can just test yourself and try that out. All right.