Okay, so the topic of this video is to kind of compare and contrast solutions that are hypotonic versus ones that are hypertonic. So, let's get started. Okay, well, first of all, what is a solution? Well, it's a mixture where one substance will dissolve in another and a solution generally has two parts to it.
There's the solute. It's the parts that are actually dissolved and then here's some solutes in my picture here. The S's are symbolic of the solutes. And then there's the solvent.
Now, in a biological solution, that solvent is typically water. So here I have in my animation here, I have solutes and water mixed together. Let me ask you, what makes sense? Does it make sense to say that sugar dissolved in the water or water dissolved in the sugar?
I hope it makes sense to say that the sugar dissolved in the water because the sugar dissolved It's the solute. The water caused the sugar to dissolve, so the water is the solvent. Well, here's a cell, and if we zoom on into this area right here in the cell membrane, we see the phospholipid bilayer, the vertical cell membrane right there, and this is our cell membrane, our plasma membrane. you might know that it is semi-permeable, meaning that certain molecules can pass freely, but others cannot. Well, let me add some water molecules on both sides of the plasma membrane, the cell membrane.
And let me add some solute molecules to both sides of the plasma membrane. Now, when we say the plasma membrane is semi-permeable, so water is able to pass through the cell membrane. Now, if you remember osmosis, the movement of water from high to low concentrations. So, water will generally move from the higher concentrated area to the lower concentrated area, but water is able to pass from one side of the cell membrane to the other.
But molecules like the solutes, for a variety of reasons, are incapable of passing through our cell membrane here. And for a variety of reasons, such as sometimes solutes are too large, Sometimes solutes have a charge on them that make them unable to pass through the cell membrane here. So, the plasma membrane generally can allow water to pass freely, but not the solutes.
Okay, so let's go ahead and talk about a hypotonic solution now. It's one with a lower concentration of solutes. And that is contrasted to a hypertonic solution, one with a greater concentration of solutes.
In my picture here, I've got a beaker filled with a fluid and an over-exaggerated size of a cell on the inside. Let's pretend the solution in the beaker is 80% water, 20% solute. But the solution in the cell is 60% water, 40% solute. Well, where is the hypotonic solution?
You have two choices. Which solution is hypotonic? The definition of hypotonic is one with a lower concentration of solutes.
Therefore, the solution in the beaker in this example is hypotonic because the 20% solute is a lower concentration than the 40% solute in the cell. And which solution is hypertonic? By definition, hypertonic is one with a greater concentration of solutes. That would be the solution in the cell because the 40% solute in the cell is greater than the 20% solute in the water outside the cell.
So, now that I've labeled the solutions outside of the cell as hypotonic and the solution inside of the cell as hypertonic, I want to ask you, what would happen to a cell that is placed in a hypotonic solution? This cell right here is placed in a hypotonic solution. Well, we remind ourselves the definition of osmosis. It's the movement or the diffusion of water from a high concentration to a low concentration.
Well, where is the high water concentration at? If you look at the picture, you can see 80% is a higher percentage than 60%. So, water would diffuse or enter into this cell over time. Over time, the cell would begin to swell and get larger and larger and larger to the point where it actually could even burst depending upon how much water flowed into it.
Well, let's look at this situation right here. Let's change the concentration a little bit. Now pretend the solution in the beaker is 50% water, 50% solute.
But the solution in the cell is still the same. 60% water, 40% solute. Well, what solution, which of these, choice A or choice B, which solution would be considered hypotonic? Hypotonic is one with a lower concentration of solutes. So, therefore, the solution in the cell is now considered the hypotonic solution, because the 40% is a lower percentage than the 50%.
And which solution would be considered hypertonic? By definition, hypertonic is one with a greater concentration of solutes, and that's the solution in the beaker. 50% is a greater percentage than 40%.
So, now that I've labeled this solution as hypertonic, the solution in the beaker is hypertonic in this example, what would happen to a cell placed in a hypertonic solution? Again, we remind ourselves the definition of osmosis, the movement or the diffusion of water from a high to low concentration. Where is the higher water concentration at? Look in the picture.
I see that 60% is a higher percentage than 50%. So, therefore, water would actually diffuse out of this cell. It would...
it could start to shrivel and lose kind of some of its water mass as a result. Okay, well, here is our cell again. And, like we saw before, let's go ahead and zoom into this area of the cell membrane. And when we do zoom into this area, we can...
Go ahead and again label the cell membrane, their plasma membrane, as being semi-permeable. And let me add 15 water molecules inside the cell. And let me add 5 solute molecules inside the cell.
On the outside, let me go ahead and add 5 water molecules. And let me add 5 solute molecules. Okay, so now that I set up this situation, where do these two labels go?
Does the hypotonic label go on the left or right? Does the hypertonic label go on the left or right? Well, look at the percentages. 15 waters, 5 solutes, that's a total of 20 molecules. So, we have 75% water solution, 25% solute solution.
On the right hand side, we have a 50-50 solution. 50% water, 50% solute. So, now I can go ahead and label the solution on the left. as hypotonic and the one on the right is hypertonic.
Hypotonic on the left. Hypotonic is a solution with a lower amount, a lower concentration, sorry, lower concentration of solutes. 25% is a lower concentration than 50%.
Now, what would happen over time? Remember, what does water do over time? It, through osmosis, it will diffuse, watch the water on the left, it will diffuse slowly over time.
until there's an equilibrium, a balance. Well, let's re-add our percentages. Now there's only 10 water molecules on the left.
That would be 67% water, 33% solute. Now what about the right-hand side? Over time, now that diffusion and osmosis has occurred, there are now 10 water molecules on the right-hand side.
That would also be a 67% water, 33% solute. Notice how they're equal to one another. Neither of these are hypotonic or hypertonic anymore.
Once an equilibrium and a balance has been established, this is what an isotonic solution is. And so if you've seen the word hypotonic, hypertonic, and isotonic in cooperation with one or a combination with one another, I hope that explains what those are. So, as we wrap up this video, if you're in my biology class, pause the video and try to answer these questions on a separate sheet of paper. And I hope you found this helpful. Thanks for watching.