Transcription
Okay, I want to review this slide. I left it up there at the end of the last presentation, uh, for you to practice figuring out some sentences for these diagrams. And I want to compare this slide to, um, this slide a little bit as well, this one here that we did earlier on. Okay?
So, first of all, uh, just to review on, um, the first diagram, uh, we can say here that the environment is hypertonic compared to the cell. Since all the water is exiting the cell, uh, there must be more solutes on the outside of the cell. So, the environment is hypertonic on the first picture to convert to the cell, or you can say the cell is hypotonic to the environment. That's the first one.
For the middle diagram, there is an equal number of arrows going in and out. And so, we, that would be a situation where we could say the environment is isotonic to the cell, or the cell is isotonic to the environment. They're the same.
And then on the, the third diagram on the top right, uh, this one, we would say, we look at it and see that water is going in, more water is going in than coming out. So, here we can say that the cell is hypertonic, more concentrated compared to the environment, or we can say the environment is hypo constant, hypotonic compared to the cell. For those examples.
Now, let's, um, talk about the, these are anima, these are plant cells in this diagram, diagram. And on the previous slide, they were animal cells. And there's a difference between animal cells, many differences, but one of the main differences is that plant cells have a wall around them and animal cells do not.
Now, let's backtrack again. Both cells have and it, have a membrane. So, actually, any cell has a membrane. A membrane is like a fluid, like a very floppy baggy, like a plastic baggie. And that inside of that baggie is all the stuff of the cell. And then the outside is the environment. So, every cell, whether you're a plant cell, an animal cell, or a bacterial cell, all those kinds of cells have a membrane.
If you're an animal cell, that's all you have. You just have a baggy around you. But if you are a plant cell, you have an extra layer around the baggy, which is the wall. So, you can think of an animal cell as a balloon, just a balloon. And the balloon, that the rubber of the balloon is, is the, uh, is the membrane. And you can think of a plant cell as a balloon inside of a shoebox. So, there's an extra box around there.
All right. So, let's take my, um, my animal cell, my balloon. I can put stuff in that balloon, and it can expand, expand, expand, expand. And eventually, that balloon is going to burst, like the, uh, the test tube on the far right here. That the animal cell has taken on too much water. It's expanded too much. Eventually, that cell membrane just can't stretch anymore, and it's just gonna rupture. And the word we use for that is lice, L-Y-S-E, lice. Or lice means bursting, breaking, or splitting. And so, this is an example where the cell has lysed because it's over-expanded and taken on too much water, like a balloon over-inflating.
Now, if we go to the plant cells here, if you can imagine taking that balloon and putting it inside a shoebox, it's all sealed up. And then somehow figuring out how to block the balloon inside the shoebox. Imagine you could do that. You could blow the balloon up, and it would expand, expand, expand until the balloon was pushing against the walls of the shoebox. And it would push all the sides and the top and everything. But the shoebox would stop it from over-expanding. And it would get all hard and push it against there. But it could not, it could not burst.
And that's the situation we have here in the top right picture. You can see the cell is kind of plumped up, and the contents of the cell are pushed out against the walls. But the cell isn't going to burst. Plant cells don't lyse. They can take up water until they're fully full of water, and they're put the membrane, it's plastered up against the, the cell wall like that balloon pushing against the shoebox. But, uh, the wall will protect the cell from bursting.
And this is actually how plant cells like to be. They like to be full of water and all expanded like this. And that's how cells, plants manage to stand up. When they, when you water them, they get full of water, and the cells go all nice and hard and inflated with water, and the plant, its leaves are up. And if water starts to, the plant starts to lose water, the, the cells get a bit more kind of wibbly, and the, the cell wall stays in place, but the membrane starts to shrink back as the water exits the cell. And you can see that in the top left picture on this diagram, uh, up there in the corner. You can see how the, the membrane has shrunk away from the wall. The wall is still in place, but the balloon has shriveled up inside there.
And then if that happens to the plant, then it starts to wilt. That's why plants wilt. Their, um, the cells aren't nice and hard and full of water. And so the whole thing, plant doesn't have bones in it to hold it up, so it just kind of flops over. Um, so that's the difference, one of the main differences between animal and plant cells in terms of water uptake and, and how it's important and how the cells behave. Um, plant cells will not lyse in a hypotonic environment, but animal cells will lyse if they're bathed in a hypotonic environment. All right.