Lesson video

This lesson is moving into and outta the blood: diffusion, osmosis and active transport and is from the unit transport and exchange surfaces in humans.

Hi there.

My name's Mrs. McCready and I'm here to guide you through today's lesson.

So, thank you very much for joining me today.

In our lesson today, we're going to explain how particles of substances move into and outta the blood by the processes of diffusion, osmosis and active transport.

Now throughout our lesson today, we're gonna cover a good number of keywords and they're there on the screen for you now.

You may wish to pause the video and make a note of them now, but I will introduce them to you as we come across them.

In our lesson today, we're going to first of all, look at the selectively permeable membrane.

Then we're going to look at moving small particles, through the membrane, before finally looking at moving large particles, through the membrane.

So, are you ready to go? I am, let's get started.

So, we know that blood is a fluid that is moved around our body by our heart.

This is all part of the circulatory system and in blood there are many things.

So, it contains lots of different things, including many different cells, such as red and white blood cells.

It also contains many nutrients such as glucose, amino acids, which make proteins, water and oxygen.

And it also includes many waste products such as urea, which then goes on to form urine, lactic acid, that's the stuff that makes our our muscles really burn when we're doing short sharp exercise and carbon dioxide.

So, these and many, many other things are contained within the blood, which is the fluid that is moved around our body.

And we're gonna have a look at how some of these things either get into the blood or get out of the blood in our lesson today.

But first we need to understand how that blood is moving around our body.

So, we know that it is being circulated around our body.

It is moving in great big loops and it's moving through blood vessels.

So, arteries are blood vessels that carry blood away from the heart.

Veins are blood vessels that carry blood back to the heart, but it's capillaries where fluids and nutrients and waste products.

So, all those substances in the blood get exchanged for the cells where they move into the cells or where they move outta the cells and back into the blood to be moved around the body again.

So, that exchange of substances is occurring via the capillaries only, doesn't happen via the arteries or the veins, it's via the capillaries.

And because we're talking about moving substances in and outta the blood in our lesson today, that is what we're gonna focus on.

We're gonna focus on the capillaries in our lesson today.

So, I've said that substances move between the tissue cells and the blood and they do that via the capillary cells.

So, the capillary cells are the cells which are lining the capillary walls that actually form the capillaries themselves.

And the capillaries is where the blood flows and the capillary cells make the wall that forms that tube.

And those capillaries are really close to the tissue cells.

And the tissue cells are the body cells essentially.

Now, some substances move into the tissues, whilst other substances move out of the tissues and back into the blood.

So, there's this exchange happening, through the capillary cells and into the tissues or into the blood.

So, in order for substances to move between the blood and the cells, they need to pass through a number of cell membranes.

So, they need to pass through the cell membranes of the capillary cells and they also need to pass through the cell membranes of the tissue cells.

So, if we look at the zoomed in part of the diagram on the screen, we can see the lighter pink section showing the blood, the dark red section showing the capillary cell membrane and the orange section showing the tissue cell membrane.

And the purple arrow shows how substances, need to move through the capillary cell membrane into the capillary cell cytoplasm, then back out of the capillary cell, through the cell membrane again.

Then through the tissue cell membrane into the tissue cell cytoplasm.

So, effectively substances are having to move through three cell membranes in order to move from the blood into the tissue cell cytoplasm.

So, that's quite a significant number of hurdles that substances need to move through in order to get from the blood into the the tissue cells or from the tissue cells back into the blood.

However, the membranes of both the capillary cells and the tissue cells are selectively permeable.

That means that some things can pass through, but not everything.

So, it will select what can be moved through.

So, that word selectively permeable means well, the word selectively means that some things can and some things can't.

And permeable means that things can pass through it.

So, both the capillary cell membrane and the tissue cell membrane, both of those cell membranes are selectively permeable.

Now, you might find the word partially permeable, being used instead.

Partially permeable and selectively permeable are both interchangeable terms. So, if you hear one, you can assume that it means the other instead.

So, let's look at this in a little bit more detail then.

So, we've got the same extract and zoomed in section of the diagram made even larger on the screen now.

And we know that some substances move from the blood into the tissue cells and these include oxygen, glucose, amino acids and water.

So, these are substances that move from the blood into the tissue cells.

There are other substances that move from the tissue cells into the blood and these include water, carbon dioxide, urea and lactic acid.

So, these are substances that move into the blood from the tissue cells.

So, let's quickly check our understanding.

Do the following substances move into the tissue cells or into the blood? Glucose, water, urea and oxygen? I'll give you five seconds to think about it.

So, let's have a look at our answers.

So, you should have said that glucose is moving into the tissue cells.

Water is moving in both directions.

Urea is moving into the blood and oxygen is moving into the tissue cells.

Did you get them all right.

Well done if you did.

Okay, what I'd like you to do to summarise our lesson so far is to draw and label a diagram that shows a capillary cell, a tissue cell and blood.

So, much like the diagram I've already shown you.

And on that diagram I would like you to label cells, so the capillary cell and the tissue cell.

The cell membranes and the cytoplasm of the cells.

Then once you've drawn that diagram and labelled it, I would like you to add substances to it.

So, I'd like you to show whether these substances move from blood to tissue, tissue to blood or in both directions.

And I'd like you to include water, lactic acid, amino acids, urea, glucose, oxygen and carbon dioxide.

So, that's the detail on the diagram that you are going to draw.

So, pause the video and come back to me when you are ready to check your work.

Okay, let's check our work then.

So, I firstly asked you to draw and label a diagram to show a capillary cell, a tissue cell and blood.

So, you should have drawn something, along the lines of the picture that I've got on the screen now and labelled the capillary cell in the middle, the tissue cell perhaps at the bottom and the blood on the other side in this case at the top.

Then I asked you to add labels to the cell membranes.

So, they're the dashed edges and the cytoplasm.

So, that's a central part of both the capillary and the tissue cells.

Then I wanted you to add substances to this diagram and show whether they're moving from the blood to the tissue, the tissue to the blood or in both directions.

So, you should have included oxygen, moving from the blood into the tissue cells.

The same with glucose and amino acids.

So, all of those are moving from the blood into the tissue cells.

You should have included water moving in both directions and you should have included carbon dioxide, urea and lactic acid moving out of the tissue cells into the blood.

So, just check your arrows, make sure you've got those pointing in the right direction and well done.

So, that is gonna form the basis of the rest of our lesson, so do make sure it's correct.

Okay, let's move on to the next section, which is gonna look at how small particles move, through the membrane.

So, small particles include oxygen, carbon dioxide and urea.

That's what we're talking about when we are talking about small particles.

So oxygen, as we know moves from the blood to the tissue cells and carbon dioxide and urea move from the tissue cells into the blood.

So, oxygen is a nutrient and carbon dioxide and urea are both waste products.

Now, all of these particles are small enough to simply move through the membrane directly.

They don't need any help to do that.

They can just move through the membrane.

And in order to do that, they move by the process of diffusion.

So, these particles are moving from an area of higher concentration to an area of lower concentration and that is how we define diffusion.

It is the net movement, so the overall movement of particles from an area of higher concentration to an area of lower concentration.

So, these particles are moving down the concentration gradient and because of that, it is a passive process.

It does not require energy, it'll happen on its own accord.

So, in this example, the oxygen is moving from the higher concentration on the left side of the screen to the lower concentration area on the right hand side of the screen.

So, whose description of diffusion is most accurate, Lucas, Sam, or Aisha? So, Lucas says diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration.

Sam says, diffusion is the net movement of particles from low to high concentration using energy.

And Aisha says diffusion is the movement of particles from low to high concentration through a net membrane, but whose is correct? I'll give you five seconds to decide.

Okay, so hopefully you've chosen Luca's definition as the most accurate description of diffusion.

Well done if you did.

Now, water is also a small particle and water can also move passively, through the selectively permeable membrane from an area of higher concentration to lower concentration of water particles.

But this process has a specific name.

It's effectively fancy diffusion, but we call it osmosis.

So, osmosis is specifically about the movement of water, but it must also involve a selectively permeable membrane and water moving down the concentration gradient from higher water concentration to lower water concentration.

And we can see that in the diagram that on the left hand side, water is in much greater concentration than on the right hand side and therefore water will move from left to right, down the concentration gradient.

So, this is called osmosis and this is only to do with water.

No other molecules can move by osmosis, only water.

Now if water is more concentrated inside the cell, water will move from the cell into the blood.

So, we can see that there are more water particles, within the cell than there are in the blood and therefore water will move from high to low concentration from the tissue cells into the blood.

However, if the reverse situation is true, if there is more water in the blood than there is in the tissue cells, then water will still move from high to low concentration, but instead it will move from the blood into the tissue cells.

So, it's still moving from an area of higher concentration to an area of lower concentration of water.

But it depends where the higher concentration is as to whether water is moving from the tissue cells into the blood as on the left hand side of the screen or from the blood into the tissue cells as on the right side of the screen.

So, if you are dealing with an osmosis example in an exam question for instance, you need firstly to identify where the higher concentration is of water and where the lower concentration of water is and then you are moving from high to low.

So, let's quickly check our understanding of that then.

So, water moves between the blood and tissue cells by diffusion, true or false? I'll give you a few seconds to think about it.

So, hopefully you've said that is false, but can you justify your answer? So, hopefully you have said that water is moving from high to low concentration and therefore the second justification is correct.

Well done if you spotted that.

So, what I'd like you to do now is to consolidate what we've just covered.

So, on the diagram that you have already drawn, I would like you to add the words diffusion or osmosis to the molecules that we've just studied.

Then I would like you to define diffusion and osmosis.

Write standard definitions for those two terms, before finally considering this scenario.

So, diffusion and osmosis can occur through any selectively permeable membrane, not just between blood and tissue cells.

And Laura's mom's friend has to have kidney dialysis, because her kidneys don't work properly.

So, the dialysis machine removes waste products from the blood just like the kidneys do.

So, what I would like you to do is use your knowledge of diffusion and osmosis to explain how excess water and waste urea move out of her blood and into the kidney dialysis machine.

So, take your time, really think very carefully about what we've covered so far and apply your understanding to Laura's scenario and come back to me when you are ready.

So, on the diagram that you've already drawn and labelled, what I wanted you to do is add the words diffusion or osmosis to the molecules that we've studied in this section so far.

So, we have looked at oxygen, carbon dioxide, urea and water, but how do they move through the membrane? Well, oxygen moves by diffusion, so does carbon dioxide and so does urea.

What about water? Well, in this case, water is moving by osmosis.

Remember, osmosis is water specific.

Then I asked you to write standard definitions for the terms diffusion and osmosis.

So, your definition for the term diffusion should be that diffusion is the net movement of particles from an area of high concentration to an area of low concentration and that it is a passive process which does not require energy.

Your definition for osmosis should be that osmosis is the net movement of water particles from high concentration of water particles to low concentration of water particles, through a selectively permeable membrane.

But this is also a passive process which does not require energy.

So, do check your definitions over, make sure you've got 'em from high to low concentration.

You've noted this term that they're passive and therefore they don't require energy.

So, just make sure that your work is correct.

And then finally, I asked you to consider the scenario with Laura.

So, Laura's mom's friend has to have kidney dialysis.

So, how does a kidney dialysis machine remove waste products from the blood just like the kidneys do? Well, you should have said something along the lines that water is at a higher concentration in the blood than in the kidney dialysis machine, and therefore water will move from the blood by osmosis into the dialysis machine.

Whereas urea, although that is also at a higher concentration in the blood than the dialysis machine, it'll move by diffusion into the dialysis machine.

So again, just check your work over, make sure you've got those processes correct.

So, osmosis for water and diffusion for urea and that they're both leaving the blood and entering the dialysis machine.

And well done.

That was quite tricky.

Okay, so let's now move on to the last section of our lesson today, which is about moving large particles through the membrane.

Now by large particles we mean glucose, amino acids and lactic acid.

So, that's what we're gonna have a look at now.

How did these particles, which are really quite bulky, move between the blood and the tissue cells? Because these are large particles, they are quite complicated in their structure and unfortunately they can't move freely through the cell membranes.

Their passage is blocked, they're just too big, they can't move through the cell membrane, so they need another way of being moved from the blood into the tissue cells.

So, how does that happen? So, large molecules such as glucose are quite complex and they need to be assisted through the cell membrane, because they can't just move through the cell membrane by their own accord.

And they're assisted by proteins called carrier proteins which sit within the cell membrane.

So, looking at the diagram on screen there, you can see that the inside part of the cell, the cytoplasm is at the bottom of the diagram and the molecule that is being transported is on the outside of the cell.

Now, the cell membrane is shown as two dashed lines.

Now that's not just the top and the bottom of the whole cell.

That is the cell membrane itself and the carrier protein is embedded within that cell membrane.

So, the cell membrane has these two edges, an inner edge and an outer edge to it and the carrier protein sort of sits inside embedded, within that cell membrane with the cytoplasm and the inside of the cell below it as in the diagram and the molecule that needs to be transported, sitting outside the cell in this example.

So, these carrier proteins are assisting the movement of large molecules through the cell membrane.

And in order to do that, the carrier proteins need to change shape to transport the molecule through the membrane and to change shape requires energy and therefore requires energy in the form of ATP, which is the currency of energy in the cell.

So, this therefore uses the process of active transport, active meaning using energy.

It requires energy in order to function and transport because it's something from one place to another.

But how does this work more in more detail? Let's have a look.

So, the first thing that happens is that the molecule that is going to be transported has to bind to the carrier protein.

So, it kind of enters and engages with the carrier protein.

On that happening, the carrier protein can then use energy in the form of ATP and change shape.

So, you can see that the carrier protein has changed shape there in the diagram and the molecule is now sort of embedded within the carrier protein and the molecule can continue to change shape and release the molecule that is being moved, transported out to the other side and therefore in this case into the cell itself.

So, the molecule binds to the carrier protein, then energy is used to change the shape of the protein and allow passage of the molecule through the membrane, so that it can be released on the other side.

So as I've said, this movement, this process is called active transport and this involves particles moving, usually against the concentration gradient, therefore from low concentration to high concentration.

So, we can see that in the diagram that there are fewer molecules on the right, rather than the left, but they're moving from right to left from lower concentration to higher concentration.

And this requires energy, it requires energy to physically move these substances for the carrier protein to change shape.

And because it requires energy, it is an active process, which is where the term active transport gets its name.

So, let's just check our understanding.

There are a number of words there and some of them need to be used to complete the sentences.

So, I'll give you a few seconds to think about it and then we'll check our work.

Okay, so let's see what you've put.

Active transport involves the movement of particles from low to high concentration.

This requires energy in the form of ATP.

Did you get them all right? Excellent job if you did.

Well done.

So, what I'd like you to do to consolidate the final part of our lesson is go back to that diagram firstly that you drew back in task A and other words active transport to the molecules that we've just studied.

Then I'd like you to write a definition for this term active transport.

What would the standard definition be if you were to look it up in the dictionary or in a textbook? So, write that down on your paper and then I'd like you to describe using diagrams to help you how this process of active transport actually occurs.

So, think about what I've shown you.

Think about the diagrams that I've used and create your own version of that to show how carrier proteins sitting within the membrane, help to move larger substances through the membrane.

And then when you finish that, I've got a real challenge question for you.

So, lactic acid is produced during anaerobic respiration and only a very small amount of energy is produced in this version of respiration.

So, can you explain why the fact that a very small amount of energy is released through anaerobic respiration, might be problematic when trying to remove lactic acid from cells? So, really have a think about that, try and join all those dots up.

Now take your time, pause the video and come back to me when you are ready.

Okay, how did you get on? Let's go and check your work then.

So, on the diagram that we drew right at the very beginning, I wanted you to add the term active transport to the molecules that we've just studied.

So, that includes glucose, amino acids and lactic acid.

Then I wanted you to add a standard definition for the term active transport.

So, your definition should be that active transport is the net movement of particles from low concentration to high concentration.

And you might have added that that is against the concentration gradient.

You should also have said that this requires the use of a carrier protein and that it requires energy in the form of ATP, because it is an active process.

So, do check your definition over, make sure you've got all of those really key parts and that it is correct.

Then I wanted you to use diagrams to help you describe the process of active transport and how that happens using carrier proteins, sitting in the membrane.

So, you might have shown a similar diagram to the one I've drawn and said that the molecule that is being transported, binds to the carrier protein.

Then the carrier protein changes shape, requiring energy in the form of ATP and then the is released on the other side.

Again, check your work over, make sure you've got all those important points, that your diagram is really nice and clear as well and properly labelled too.

Well done.

And then finally, I had this little brain teaser for you.

So, lactic acid is produced during anaerobic respiration in animals and it only produces a very small amount of energy.

So, can you explain why this might cause a problem when we're trying to remove lactic acid from cells? So, perhaps your answer included these points that firstly, lactic acid is a waste product.

It's made by the cell, it needs to be got rid of, so it needs to be removed from the cell, but it can't diffuse outta the cell because it is too large.

So, it has to be transported by carrier proteins, through the membrane via the process of active transport.

Now, active transport requires energy, but energy is in short supply during aerobic respiration.

So, that means that moving lactic acid outta the cell, may not be the thing that the cell is able to do, given that there isn't very much energy around.

And so lactic acid might build up in the cell instead and that will cause damage to the cell.

So, you can see it's a bit of a conundrum really, that the cell faces, does it get rid of the lactic acid and then not have enough energy to do other things or does it keep the lactic acid and run the risk of being damaged by it in the attempt to carry out other functions that it's trying to do instead? So, well done if you managed to put an answer together for that.

That was a really tricky question, but I hope that's helped you bring some of your ideas together in this lesson and well done that was a valiant effort throughout.

So, good stuff.

So, just to summarise our lesson today then.

Substances move between the blood and the cells, through the selectively permeable cell membranes.

And we've seen that small particles can move by diffusion.

This includes oxygen, carbon dioxide and urea, whereas water moves by a special version of diffusion, called osmosis.

Now, we know that diffusion and osmosis involve the net movement of substances, down a concentration gradient, but large particles don't have the luxury of moving by diffusion.

They need to be moved by active transport and that requires energy.

So, that brings our lesson to a close.

Thank you very much for joining me.

I hope you enjoyed it.

I hope you've learned lots too.

I've certainly enjoyed myself today and I hope to see you again soon.

Bye.