You know what word gets thrown around a lot, but is actually pretty challenging to understand? osmosis but it does answer some great questions like why would it be deadly to give someone an IV of pure water or why would a saltwater fish placed in freshwater experience major problems we'll answer these questions as well as explain the process of osmosis now first understand that osmosis is the movement of water and that really is a type of diffusion often when you're talking about osmosis you're talking about the movement of water Through a semi-permeable membrane, like a cell membrane. A cell membrane has openings small enough for water molecules to pass, but it will not allow larger things like salt molecules to freely pass.
At least, not without assistance. Osmosis is a type of passive transport, meaning that it doesn't require energy. I mentioned osmosis is a type of diffusion.
And similar to what you might have learned about with diffusion, molecules, in this case water, travel from areas of high concentration of water to low concentration of water. But there's another way to think about water movement in osmosis. A low water concentration likely means there are a lot of solutes. Solutes are substances like salt or sugar that can be dissolved within a solvent, like water. Water has the tendency to move to areas where there is a high solute concentration, which means there's less water concentration.
So if you want to easily figure out where the water will travel, look to the side where there is a greater solute concentration. So let's imagine you have a box with a semipermeable membrane in the center. And remember this membrane will let tiny things pass through it, like water and gases, but not large solutes like salt. We'll label one side of the box A and one side of the box B. If you have pure water on both sides of the box, Those water molecules, they're moving.
Water molecules, they like to move. But the net movement of water on the two sides is zero, meaning the overall change in direction of movement is zero. Now let's imagine on side B you dump a huge amount of salt there.
So which direction will the water move towards? A or B? The answer is B. This area has a high solute concentration. And remember, water moves to areas of higher solute concentration.
You can almost think of the water as trying to equalize the concentrations, diluting side B. Once equilibrium is reached, the net movement of water on the two sides will be zero. But remember that water still likes to move and movement still occurs. Here's some vocabulary to know.
We call side B hypotension. hypertonic. You know that prefix hyper when you think of a hyper person?
Well, that helps me think of a high amount of something. For a hyper person, it might be caffeine. But in our case, it means a high solute concentration.
But we can't just say something is hypertonic without comparing it to something else. We say that side B is hypertonic to side A because it has a greater solute concentration than side A. In osmosis, water moves to the hypertonic side. We say side A is hypertonic to side B because it has a greater solute concentration A is hypotonic. Hypo rhymes with low, which helps me remember that it's a lower solute concentration, at least when compared to PsyB.
So let's do some real life examples now, because this box thing is getting a little bit boring. When someone gets an IV in a hospital, it may look like the clear fluid running through the IV is water. But it is certainly not water.
That would actually be a disaster because of osmosis. Let's say hypothetically, they're was pure water placed in an IV. Now an IV tube typically runs through a vein so that you have access to your bloodstream.
Really useful for running medication through. Blood actually consists of many different types of cells. Red blood cells are a great example. So what do you think has a greater solute concentration?
The hypothetical pure water in the IV tube or in the red blood cells? Remember cells are not empty vessels. They do contain solutes. The pure water that hypothetically is running through this IV tube has no solutes. It's just pure water.
So where does the water go? Remember, it goes to the area of higher solute concentration. So it's going to go inside the cells.
The cells are hypertonic compared to the water in the IV tube because the cells have a greater solute concentration. The cells would swell with water and possibly burst. Exploding red blood cells are not fun.
If a person needs They typically receive a solution that is isotonic to their blood plasma Isotonic means equal concentration So you wouldn't have any swelling or shrinking red blood cells and that's a good thing Say you go to a pet store and you get a fish that looks like Nemo from the movie finding Nemo a clownfish Only you don't know it's a saltwater fish. What would happen if you placed this saltwater fish in fresh water? Okay, first ask yourself Where is there a higher solute concentration? In the saltwater fish cells or in the freshwater that you just placed this fish in?
Definitely in the saltwater fish cells. So where does the water go? It's going to go to the area where there's a greater solute concentration, the hypertonic side. So it's going to go into that poor fish. If you don't rescue it soon, the cells would actually start swelling.
If you looked at them under a microscope, eventually this fish could die. Now, one thing to clarify, saltwater fish and freshwater fish are not necessarily isotonic. Remember, that means equal concentration to their surroundings.
But they have special adaptations that allow them to live in their environment. And usually they can't make a major switch from a saltwater environment to a freshwater environment. Now, not all fish have this problem. There are some fish that have this amazing adaptation to switch between fresh and saltwater.
and they have to deal with this osmosis problem frequently. Salmon, for example. I think if I had to be a fish, I'd be a salmon. You know, osmosis also explains how many kinds of plants get their water.
Sure, many plants have roots, but how does the water get into the roots? When it rains, the soil becomes saturated with water. The root hair cells have a higher concentration of solutes within them than the solutes in the saturated soil. So the water travels to the area that is hypertonic, and in this case, the roots.
Or if you live in an area that gets ice, you might be used to salt trucks salting the road. Great for icy roads. Not so great for the plants that live right by the roadside. If you dump a bunch of salt on these plants, you can make the soil environment around them very salty. Very high in solute concentration.
Very hypertonic compared to... The root hair cells. So how does the water move into the root hair cells now?
Well, it doesn't. Many plants by salted roadsides die. The same kind of thing can be tragic for slugs.
We think slugs are misunderstood, almost cute gastropods. We understand that many gardeners find them to be pests in their garden, but we really don't like it when we hear of salt being placed on slugs. It really is death by osmosis. Basically, if salt is dumped on a slug, you are making that outside environment of the slug very hypertonic.
The slug is hypotonic to the salt. Remember, the water will travel to the area of higher solute concentration, to the hypertonic side, so the water that was in the slug, the moisture that this slimy slug needs, travels out of the slug, and the slug dehydrates. You can get really technical with osmosis. In advanced biology, you explore a formula to calculate water potential, and that in osmosis, water travels to areas of lower water potential, basically areas of lower free energy.
We won't be going into the water potential calculations with this short clip, but we like to think about water as loving solutes and avoiding pressure whenever determining where will the water go. Water is one of the most important molecules for life. So the big picture here is in all topics of life, it is really important to understand how water travels.
Practice makes perfect, and so we have some practice problems if you would like to test out your osmosis skills. Well, that's it for the Amoeba Sisters, and we remind you to stay curious.