Welcome back to Anatomy and Physiology 1 Laboratory. My name is Kevin Tokoff and in this video we're going to discuss the key concepts from Exercise 3, which has to do with cell transport. In the first couple of slides we're going to discuss the basics of diffusion and osmosis.
But before we do that, let's come down here and define a few important terms. First of all, we have the concept of kinetic energy. So every particle, every molecule on the biochemical level in the cell has...
motion. You really can never slow a molecule down to not moving at all. They're always moving, and the energy due to that movement is kinetic energy, okay?
And faster objects or particles have a greater amount of kinetic energy, and this kinetic energy that all of these particles have can help them traverse the membrane if they're allowed to, okay? From one side of the membrane to the other. Now, the cell membrane that all of our cells have are select... permeable or they're called selectively permeable membranes.
What does that mean? Well this membrane might allow some molecules to move through but it won't allow others to go through the membrane. Okay so it's selective as to which particles it will allow across the membrane. We'll discuss that in more detail on the next slide. And the same thing goes for concentration gradient.
We'll look at that on the next slide later. But a concentration gradient is a physical state in which if you look at either side of the membrane for a given type of molecule, there's a different concentration on either side. So for example, let's look at these blue circles here. Notice on this side at the top, there's a lot of blue circles, whereas on the bottom, there's only a couple. So therefore, we would say there's a concentration gradient.
There's a lot more of these blue circles concentrated on the outside than on the inside. And actually notice the same thing goes for these orange triangles. There's a concentration gradient, right? So how does this all relate to diffusion?
Well, first of all, with diffusion, we're going to talk about the transport only with respect to the solute. So a solute particle for these purposes is really something dissolved in the watery medium of the cell or outside the cell. So all this out here, this is water. All this inside the cell here is water.
But we're going to talk about this with respect to the solute. Now, we just mentioned that for this... blue circle, which is a solute in this case, it has a concentration gradient with the higher concentration being outside the cell up here and then a much lower concentration being on the inside of the cell, only two particles there.
So the basics of diffusion is that we consider the solute, these blue circles, diffusion means that the solute will always move from an area of high concentration to an area of low concentration. So let me repeat that. Diffusion means that the particle will move across a membrane from an area of high concentration to low concentration, which in this case means moving downwards. In this case in the middle, we have facilitated diffusion. This is another kind of diffusion that requires a protein, but that's not the point.
It's still a type of diffusion and notice we have these orange triangles, which will diffuse across the membrane from their area of high concentration into the cell where the concentration is low. make sure you understand the definition of diffusion. And also make sure you understand that diffusion is what we call a passive process. Passive processes do not require energy, and so they just happen spontaneously because it's natural or it's energetically favorable for these molecules to move from high concentration to low concentration. And we'll only consider passive processes in this laboratory course.
In the lecture, you'll go over both of these passive and active processes. processes like over here on the right which actually will require energy. Alright, so a little bit more on diffusion.
So first of all let's talk about this on the right. Selectively permeable membrane, what does that mean? Well here's an interesting diagram that kind of depicts this. Here over here in yellow, these molecules, these are lipid soluble molecules for example, these can actually diffuse across the membrane.
Notice we have an arrow here that depicting that these molecules can cross. These red ones can cross. they require a protein, but regardless they can still cross the membrane. But notice these green molecules up here, this arrow that's bouncing off of the membrane, so to speak, this is trying to signal to you that these do not cross.
In other words, this membrane is selective as to which of these three solutes it allows to cross and which it doesn't. It allows the red ones and the yellow ones to cross, but the green ones it does not allow. Therefore, we would call this membrane selectively permeable, and in general all of our membranes are.
Over here we have concentration gradient. Here's another look at it. So here's a membrane right in the middle and we have one physical space over here on the left and another on the right.
And these red circles are meant to be the solute particles. Notice on the left we have a high amount of these, relatively speaking, and on the right side we have none. So high concentration on the left, low concentration on the right.
Therefore, we have a concentration gradient, which remember means that It's a physical state in which both sides of this semi-permeable membrane or selectively permeable membrane have different concentrations. And if you have a concentration gradient, you will have diffusion. So in other words, the red particles here would diffuse from left to the right side.
So that's diffusion. Alright, let's move on to osmosis. There's a few critical concepts here. So osmosis is coming at movement across a membrane from a different perspective.
When we looked at diffusion, we were considering only the solute. These blue circles move across, these orange triangles move across from high to low. Now we no longer consider the solute.
Now we consider the movement of water. So we're sort of saying the solutes do not move, only the water moves. Well, how does it move? Well here we have a picture. Notice over here on the left side of this membrane, which is in the middle going vertically, on the left side we have a lot of solute particles and on the right we have none.
Okay, so in other words, high concentration of solute on the left, low concentration of solute on the right. So if we don't allow the solute particles to move but we allow the water to move now, the water will always move in the direction of higher salt concentration or higher solute. In other words, what that means is the water will move toward the side of the membrane that has a higher solute concentration. So the water in this case would move towards the side with the higher salt over here on the left.
And so when you elapse some time and you go over here on the right side, this picture, you notice the water has diffused over or osmosed over to the left side to equalize the concentrations. So the key with osmosis is... Water will always move in the direction of higher salt concentration. So in this case, you're coming at it from a different perspective. That is the perspective of water.
Okay, now we have three other important concepts here, and that's the concepts of hypotonic, isotonic, and hypertonic solutions. In the solution, what we're considering to be the solution is outside of these yellow cells. So outside, this outside environment. So let's look at hypo first, hypotonic. Hypo means below or underneath.
So what we're saying with hypotonic solution is the solution outside the cell has a really low salt concentration, very low, okay? And so if it's low out here, that means it's relatively higher in the cell. And so which direction will water move, or osmos?
Well, it'll always move in the direction of higher salt concentration. So if it's lower out here, water will move into the cell, okay? And in this case, if you have too much of a hypotonic solution, the cells will burst or lyse because too much water is moving in. Almost like you're blowing up a balloon, but you blow too much air into it and it pops.
Okay? Now let's come over here to the right side. Now we have a hypertonic solution.
Hyper means above or on top of. And so the solution out here has a much higher salt concentration. And relatively speaking, the inside of the cell would have a lower salt concentration.
So which direction will water move? Well, it always moves towards the higher salt concentration, which is out here in the outside solution. So you see water moving out here.
And so if you have a lot of water moving out of the cell, the cell is going to kind of shrivel up or what we call cremate. And so the cell will sort of shrink, so to speak. Okay.
So that's what happens in a hypertonic solution. So right in the middle is what we call an isotonic solution. And this is where both The outside solution and inside the cell have approximately the same salt concentration, and this is what you want. And so the osmosis of water out occurs at the same rate as the osmosis of the water in. And so there's no net change in the size of the cell.
It doesn't shrink as in over here or shrivel, and it doesn't blow up and burst as here on the left. And so this has a clinical application. When you actually deliver or administer IVs, you want to make sure that the IV salt concentration is isotonic to the person's cells as much as possible because you don't want situations where their cells shrivel up or burst, obviously. So isotonic solutions are important for that. Okay, so hopefully this makes sense and make sure you can identify these three situations if given an egg.
Remember in lab we looked at actual models of eggs that have been soaked in different concentration sugar solutions. Make sure you recognize what kind of solution each was in. Was it hypotonic, isotonic, or hypertonic?
And then also make sure you know the definition of osmosis and how it works. So now on this last slide, we're going to discuss the critical concepts from this chapter, all right? And this is mainly how diffusion rate varies with some physical parameters, okay?
Remember, diffusion rate was just the speed that diffusion occurred, okay? So how can you increase the diffusion rate? Remember, these are some of the important things that you should know.
Diffusion rate increases when molecular weight decreases. Remember, we looked at those dyes, and the heavier dye diffused more slowly, whereas the lighter dye diffused more slowly. quickly.
And so that means lower molecular weight particles will have a higher diffusion rate. Okay, now diffusion rate and molecular weight you see, and I've color-coded it, are inverse. One goes up, the other goes down.
All of the others are actually a positive relationship. So if diffusion rate increases, these also increase and vice versa. So if you want a higher diffusion rate, you should have a higher surface area to volume ratio. Remember in the lab when we cut up the The little gels and the more surface area that was exposed to the vinegar, the faster the diffusion of the blue dye occurred out of the gel.
Okay? So remember, a higher surface area to volume ratio means a higher diffusion rate. And also ones that we didn't actually have an explicit experiment for, higher temperature increases diffusion rate. So if you actually took those gels that we looked at with the blue dye and put them in vinegar, you put one at 300 degrees and one at 100, the one at 300 would diffuse more quickly because temperature increases the diffusion rate. Then the last thing is the concentration gradient increasing.
So if you have a higher concentration gradient, you'll have a higher diffusion rate. So for example, let's consider these situations down here. Which one has a higher concentration gradient?
Well on the right side of each of these, situations there's no red particles. But if you look at the left side, over here I have a higher concentration and I have like nine of these particles. Over here I still have the red particles but there's only four.
So in which case is there a bigger difference between the left and the right side? Well there's a bigger difference in the case over here in the first case. So because there's a higher concentration gradient, the diffusion rate is going to be much quicker on the left side.
In fact what I could do shorten this arrow to denote that this over here is going to have a lower diffusion rate just because it has a lower concentration gradient. Alright, so make sure you understand these concepts and can apply those on the quiz. Alright, now I'm also going to have a video over Brownian motion and that will be separate from this one.
It'll be a really short video so make sure you watch that video as well and understand what Brownian motion is. Alright. So hopefully this video helped clear up some of the problems or issues you had with some of these concepts. And make sure that you study these for the quiz that we will have on Tuesday when we resume.
Alright, see you in class.