Lesson video

- It's Mrs. here again, and we are going to be looking at diffusion today in Science.

And this topic falls under our Cells unit within Science.

And you are just going to need somewhere to write down your ideas today.

So a book and a pen or a digital device, whatever you prefer, and once you've got that and you are ready to begin, let's get started.

So the title of today's lesson is "Diffusion", and what we're going to be doing today is describing and explaining what diffusion is as well as giving some examples within the human body, particularly in the gas exchange system.

Again, this falls under your Cells unit within Science, and you are just going to need somewhere to write down your ideas today.

Before we start, let's have a look at some keywords that are gonna pop up here and there in our lesson today.

The first one is this word "net".

Now, when we're talking about "net" in science, sometimes we can actually mean a net used to catch things, but today, we're going to be talking about net movement.

Net movement is just another way of saying the overall movement.

So a net movement just means the overall movement.

We're gonna talk a lot about particles today.

And just as a reminder, a particle can be an atom or a molecule, and that is normally represented by a sphere or a circle within a model or diagram.

So wherever we see some circles today, they are going to be representing our particles.

Concentration is another word that's gonna pop up later on in the lesson, and that just refers to the amount of particles in a given volume, in a given space.

So if we had the same amount of space in two containers, and container A had more particles in the same amount of space, it would have a higher concentration of particles.

And our last keyword today is rate.

Rate is just referring to how quickly something happens.

So something that has a high rate takes place very, very quickly.

Something that has a lower rate takes place really, really slowly.

So let's just have a look at the four main things that we're gonna be covering in today's lesson.

First of all, we're gonna define this term diffusion.

Then, we're gonna look at diffusion taking place within cells.

We're gonna explain some of the factors that affect the rate.

Remember, that means how quickly, the rate of diffusion, or how quickly diffusion takes place.

And then finally, we're gonna look at how diffusion happens within our lungs in the gas exchange system.

But let's start by looking at the definition.

So imagine we've got a room, and in the corner of the room, we've got some particles.

There is a high concentration of particles in the corner of this room.

That is where we would find the most particles.

When diffusion takes place, the particles start to move around.

Now, particles are always moving.

In diffusion, the particles move from an area of high concentration to an area of low concentration.

We know that in this room, the highest concentration of particles was in the bottom-left corner.

The particles will move from this area of high concentration to an area of lower concentration, away from this corner of the room.

This will continue to happen because the particles will continue to move, until eventually, they spread out more and more until we have an equilibrium.

An equilibrium is a point in which the particles are evenly spread out within the space.

We can see here, in our room now, there is no particular area that has a higher concentration of particles.

We would say that the particles have reached an equilibrium.

Even when the particles have reached an equilibrium, they will continue to move around, but they will stay spread out across the room.

We can take this idea of particles moving in a room to get our definition of diffusion.

Diffusion is the net movement of particles from an area of high concentration to an area of low concentration.

And this will continue to happen until eventually an equilibrium is reached.

Remember, an equilibrium is where the particles are at equal concentrations at all parts within the container.

Okay, let's do some quick check-for-understanding questions.

I'm gonna read the question, I want you to then pause the video, choose your answer, and once you're happy with it, resume, and you can check whether it's correct.

So the first question says: Diffusion is the net movement of particles from an area of.

Pick the one that you think finishes this sentence.

Well done if you picked A, diffusion is the net movement of particles from an area of high concentration to an area of low concentration.

Second question: True or false? At equilibrium, the particles stop moving.

Well done if you said False.

Now have a go at justifying your answer.

Well done.

At equilibrium, particles don't stop moving because particles are always moving randomly.

That brings us nicely onto Task 1 for today's lesson.

There are two really short questions for you to have a go at.

The first one: Define the term diffusion.

Remember those keywords at the start of the lesson.

You might want to pop a few of those in there.

And then question 2 or question B: Explain what is meant by the term "equilibrium".

Write down your ideas and pause the video.

Once you are ready to check your answers, resume the video and come back to me.

Okay, let's look at the answers then.

First one, diffusion is the net movement of particles from an area of high concentration to an area of low concentration.

And equilibrium is when the concentration of particles is equal in all areas.

We can see with the start of the word "equilibrium", kind of gives us a clue about this idea of equal concentration of particles.

Well done if you've got those correct.

If not, just add a couple of notes to help you remember for next time.

Okay, so we've got our definition of diffusion.

Let's take a look at how this diffusion happens within cells.

So diffusion is really important for allowing substances to move into or out of cells.

Let's take a look at this cell here.

We've got some particles inside the cell, and we also have some particles outside the cell.

This is an animal cell because it has an irregular shape and does not contain a cell wall.

In this diagram, there is a higher concentration of particles outside of the cell compared to inside of the cell.

We can see this because there is significantly more purple circles, representing particles, outside of the cell membrane than there is inside of the cell membrane.

Diffusion would happen in this scenario.

If the particles were able to move through the membrane, there would be a net movement of particles into the cell.

And this would keep happening until the concentration inside of the cell was equal to the concentration outside of the cell.

So in this scenario, we started with a higher concentration of particles outside of the cell compared to inside of the cell.

Diffusion would take place until there was an equal concentration of particles inside of the cell compared to outside of the cell.

Let's have a look at another example.

Again, we have an animal cell, and we have some purple particles.

In this diagram, there is a higher concentration of particles inside the cell compared to outside of the cell.

I bet you can already start to figure out what's going to happen.

If the particles are able to move through the membrane, there will be net movement of particles out of the cell.

And this will continue to happen until the concentration is equal inside and outside of the cell.

In this scenario, we started a higher concentration of particles inside of the cell.

Diffusion would take place until the concentration of particles is equal inside and outside of the cell.

Okay, let's do some quick check-for-understanding questions.

Question 1: Diffusion always occurs through a cell membrane.

Well done if you said False.

Can you pick the correct justification as to why this is false? Okay, this is false because diffusion can happen at any point.

Okay, we started with an example, of diffusion happening in a room.

There were no cell membranes in that room, but the particles still diffused from an area of high concentration in the left corner of the room to an area of low concentration at the opposite side of the room.

Next one: Particles can only diffuse into cells.

True or false? Well done if you said False.

Have a go now at justifying your answer.

Well done if you said that particles diffuse in the direction of the concentration gradient.

Sometimes, particles diffuse into cells, but sometimes particles can diffuse out of cells.

It will depend on the direction of the concentration gradient.

Okay, Task 2 for today, I would like you to add particles, and these can be represented by circles, into the diagram below, showing diffusion taking place.

There are three scenarios.

I want you to draw a scenario where diffusion would take place and particles would move into the cell, I would like you to draw a scenario where diffusion would take place and particles would move out of the cell, and I would like you to draw a cell which shows an equilibrium.

Pause the video and spend a good amount of time on this.

Once you're ready to check your diagrams, resume the video, and I will show you my answers.

Okay, let's have a look at some of these answers.

So for A, I would like to see a much higher concentration outside of the cell than into the cell, because this way, diffusion would happen where particles would move from a high concentration outside of the cell to a lower concentration inside of the cell.

In B, I want to see the opposite, so a much higher concentration inside of the cell compared to outside of the cell.

And for scenario C, I would like to see an equal number of particles inside of the cell than there is outside of the cell.

Fantastic.

So we've looked at diffusion, and we've looked at how this takes place in cells.

Now let's have a look at how we can affect the rate of diffusion, remembering that that keyword "rate" just tells us how quickly something happens.

There are several factors that can affect the rate of diffusion, or can affect how quickly diffusion takes place.

The first one is temperature.

The higher the temperature of the scenario, the higher the rate of diffusion.

Next, we have surface area.

The greater the surface area, the higher the rate of diffusion.

And lastly, we have concentration gradient.

The steeper the concentration gradient, the higher the rate of diffusion.

We're gonna look at each one in a bit more detail now.

Let's start with temperature.

So we've already said that the higher the temperature, the higher the rate of diffusion, the quicker diffusion will take place.

Let's have a look at why that is.

At high temperatures, particles have a lot of energy, and they move around much, much quicker.

We can see that is represented in our model on the screen by the size of the arrows.

The arrows are quite large.

That is telling us that these particles are moving around a lot.

However, at lower temperatures, particles don't have as much energy.

So they don't move around as quickly, they don't move around as much.

The diffusion happens at higher temperatures much quicker because the particles have more energy to move quicker.

And we know that diffusion involves the movement of particles.

The more energy particles have, the quicker they are able to move around.

Now, let's look at surface area.

We've said that the greater the surface area, the higher the rate of diffusion.

Let's take a look at this by comparing two cells.

I've got a root hair cell, and I've got a palisade cell, which is found in leaves.

The root hair cell has a larger surface area compared to the palisade cell.

This is because of the shape of the root hair cell.

The elongation of the root hair cell means that it has a much larger cell membrane.

A cell with a larger surface area has space for more particles to move through the membrane.

A higher surface area means it has a larger cell membrane.

The higher the surface area, the more space that particles have to move into or out of a cell, and therefore the quicker diffusion takes place.

The last one is concentration gradient.

We see the steeper the concentration gradient, the higher the rate of diffusion.

We've got this scenario here, which shows a steeper concentration gradient.

Here's another scenario that has a shallower concentration gradient.

The steepness of the concentration gradient is determined by the difference in concentration within two places.

We can see that in the steeper concentration gradient, there is a much higher difference between the concentration inside of the cell compared to the concentration outside of the cell.

In the shallower concentration gradient, there is less of a difference in concentration in the cell and out of the cell.

The steeper the concentration gradient, the more particles will move in the direction of the lowest concentration.

More particles are moving, meaning that diffusion is taking place at a higher rate.

Let's stop and do some quick check-for-understanding questions.

First one: In which cell will diffusion happen quicker? Well done if you said the root hair cell.

This is because the root hair cell has a higher surface area.

Next one: Why does an increase in temperature increase the rate of diffusion? Well done if you remembered that this is because particles have more energy.

The more energy particles have, the quicker they are able to move and the quicker diffusion can take place.

Next one: Why does an increase in surface area increase the rate of diffusion? Well done if you said that this is because there is more space for particles to diffuse.

And next one: Which scenario is where diffusion into the cell would happen the quickest? Read that question carefully to make sure you're happy with your answer.

In this scenario, it would be A.

This is because there is a higher concentration outside of the cell compared to inside of the cell.

So I know that particles are moving into the cell.

But unlike scenario B, there is a steeper concentration gradient, and therefore diffusion would happen quicker.

For Task 3 today, again, there are two short questions for you to have a go at.

The first one is a fill-in-the-blanks, which is explaining how one of those factors can increase the rate of diffusion.

And question B is just listing two other factors that increase the rate of diffusion apart from temperature.

Have a go at that now.

Pause the video, and once you're ready to check your answers, resume, and we'll go through them.

Okay, let's go through these answers then.

First one, increasing the temperature of particles increases the rate of diffusion because the particles will have more energy and will move more quickly.

The two other factors apart from temperature that increase the rate of diffusion are: steeper concentration gradients and larger surface area.

You need to be specific there because the question asked you about what will increase the rate of diffusion, not just what will affect the rate of diffusion.

Make sure you're happy with your answers before we move on.

If you need to pause video to make corrections, do that now.

Okay, that takes us nicely on to our last lesson outline for today, and we're gonna have a look now at diffusion taking place within the lungs.

Diffusion is super important for humans, and actually, most living things on our planet, because it allows important substances to move into cells to carry out living processes, but also allows cells to get rid of any waste or move things around an organism.

Important substances that move by diffusion include: oxygen, carbon dioxide, glucose, and any other nutrients from the nutritional systems, such as, for humans, the digestive system, that need to move around the organism.

We're just going to look at diffusion in the lungs.

Diffusion takes place in the gas exchange system, and one of the main organs in that system is the lungs.

If we were to look at the lungs more clearly, we would see that they are made of these small structures called alveoli.

If we look at the alveoli in even closer detail, we can see that next to each alveoli, there is a capillary.

On my diagram, the capillary is shown by the tube, and within that tube, we can see red blood cells.

Which substances do you think are going to diffuse here in this system? Have a good think, pause the video, and come back when you're ready to hear the answer.

Okay, welcome back.

So this is the gas exchange system, so we're talking about the diffusion of gases.

The two gases that are going to be exchanged in the gas exchange system are carbon dioxide and oxygen.

Let's take a look at how this takes place.

So this is happening in the alveoli, this is our alveoli, and the first thing that happens is the diffusion of oxygen.

Oxygen has the symbol O2, and we can see on our diagram that oxygen is moving from the alveoli into the capillary.

This is because the air in the alveoli has a higher of oxygen compared to the blood.

Oxygen will diffuse from the alveoli and into the blood.

Here, the oxygen is moving from a high concentration in the air to a low concentration in the blood.

Diffusion takes place, and the blood carries the oxygen away.

At the same time, we also have carbon dioxide diffusion out of the blood and into the alveoli.

Blood has a higher concentration of carbon dioxide than the air that we inhale.

Carbon dioxide moves from the blood and into the alveoli.

Here, carbon dioxide is diffusing from a high concentration in the blood to a low concentration in the alveoli.

Carbon dioxide is shown here by the symbol CO2.

Let's do some quick check-for-understanding questions to make sure we've understood how diffusion takes place in the lungs.

Question 1: What diffuses from the air in the alveoli into the blood in the capillaries? Well done if you said oxygen.

A nice and easy one to get us started.

Okay, next question: True or false? Oxygen diffuses from the blood into the air in the alveoli.

Once you've chosen whether it's true or false, don't forget to pick your justification.

Okay, this is false.

Actually, oxygen diffuses from the air in the alveoli into the blood, and that is because oxygen is in a higher concentration in the air in the alveoli than it is in the blood.

Remember, diffusion takes place when substances move from a high concentration to a low concentration.

This brings us to our final task of today, Task 4.

For question A of Task 4, I would like you to use the four keywords, alveoli, oxygen, concentration, and blood, to describe how diffusion takes place at the lungs.

You are only going to be talking here about the diffusion of oxygen.

Have a good go and come back to me when you are ready to check your answer.

Okay, let's have a look at this answer.

Here's my idea.

You might have got something different, but as long as you've got the key points down, I'm absolutely fine with that.

So the first thing that I've got is the idea that oxygen travels to the alveoli, or oxygen is found in the air in the alveoli.

And at the alveoli, there is a high concentration of oxygen, but in the blood, there is a low concentration of oxygen.

Therefore, oxygen diffuses out of the alveoli and into the blood.

It is diffusing from a high concentration to a low concentration.

Use my model to mark your answer, and if there's any of these key ideas that you've missed, don't forget to add them on so you remember for next time.

Right, the second part of Task 4 then, I want you to use this diagram of the alveoli and the learning that we've looked at earlier in the lesson and explain how the shape of this alveoli, 'cause it is a bit peculiar, it's a really irregular shape, how does that increase the rate of diffusion? Pause the video and come back to me when you're ready to check your answer.

The alveoli has this folded shape, and that increases the surface area and therefore increases the rate of diffusion.

And that's it for today.

Let's just quickly summarise our learning of diffusion so that we are ready to remember these key ideas should we need them again.

So the first key point that we learned today was the definition of diffusion.

Diffusion is the net movement of particles from an area of high concentration to an area of lower concentration.

And remember, we said that that word "net" means overall.

So diffusion is the overall movement of particles from an area of high concentration to an area of low concentration.

Particles will move by diffusion until they've reached an equilibrium, and that is where there is an equal concentration of particles at all areas within a space.

The rate of diffusion can be increased by increasing temperature, increasing surface area, or increasing the steepness of concentration gradient between cells.

And remember that concentration gradient is steeper when there's a higher difference in the concentration into areas.

And finally, diffusion is essential for the movement of oxygen, glucose, and nutrients in the body, and it's super important for the gas exchange processes that happen at the alveoli in the lungs, where we have oxygen diffusing out of the lungs and into the blood by diffusion and carbon dioxide diffusion from the blood into the alveoli, ready to be exhaled out of the body.

Well done for your learning today.

This has been a completely new idea, and you have done fantastically.

Don't forget to save your work, and I hope to see you again very soon.

Bye!.