Hello and welcome to today's lesson.

So the lesson today comes from the unit Diffusion, and this is the first lesson in that unit.

The title of today's lesson is "Diffusion: Moving Particles." The outcome from today's lesson is that you'll be able to explain that diffusion is the movement of particles that make up substances and how they move from an area of higher to lower concentration.

I'm Dr.

Mason.

Let's get going.

So first of all, in today's lesson, there are a number of key scientific words that is really important that by the end of the lesson you understand what they mean and how to use them.

In order to help you do this, we're gonna go through the keywords now and define them.

So the keywords are passive process, concentration, concentration gradient, net movement, and diffusion.

Let's define those words.

So a passive process is one that doesn't require any additional energy in order to take place.

Concentration is the number of particles in a volume of liquid or gas.

And related to that is something called a concentration gradient, and that's the difference in the concentration, so how many particles there are in one area compared to another.

Net movement is the overall movement of particles from one area to another.

And diffusion is defined as the net movement of a substance from an area of higher concentration to an area of lower concentration.

So throughout today's lesson, you will come across all of these words, and hopefully, by the end of the lesson, you'll be able to use them.

Let's have a look now at today's lesson.

So today's lesson is divided into three parts.

So we've got substances and particle movement, which will be coming up first.

We've got diffusion in cells, and then we've got concentration and net movement.

So we're going to start with substances and particle movement.

Substances are made up of particles, and the particles can be arranged as a solid, a liquid, or a gas.

And you can see there on the screen that the particles in a solid are in a regular arrangement.

They're very close together, they're touching and they're unable to move.

In a liquid, the particles have a little bit more space between them and they're able to move around and over each other.

And in a gas, the particles are very far apart and they can move very freely.

Now let's have a look at the movement of the particles in liquids and gases.

So you can see there the particles are constantly moving.

They're going in all different directions, so we've got random movement, and they're quite often colliding with each other.

And when they collide, they can often change direction.

You can see the liquid there is taking the shape of the container, and that the liquid particles are able to move over each other.

You can see in the gas that there's lots more space and that the particles are moving quite freely, and they will fill whatever space they have.

Now let's carry out a check activity.

So what I'd like you to do here is complete these sentences, and they're about the movement of particles, which we've just talked about.

And I want you to use the words from the list.

You'll need to pause the video while you do this, and then we'll have a look at the answers.

Let's have a look at the answers.

So we've said that all substances are made up of particles, and the particles of liquids and gases are constantly moving.

They move randomly and often collide with each other.

So well done if you got those correct.

If you didn't get them all right, you might just want to note down what the right answer is, so you know in the future.

The constant and random motion of particles causes them to spread out, and you can see in the animation here that the particles were on the right-hand side of the screen, and, as we've moved the barrier between them, that they are spreading out.

Again, it's a gas and you can see the particles are randomly moving, colliding with each other, and they're constantly moving.

And that constant random motion has led to the particles spreading out so they are evenly spread.

This movement that we've talked about only happens in liquids and gases, and that's because the particles are free to move.

They're constantly moving, constantly colliding with each other.

It can't happen in a solid because the particles are too close together.

They're in a very fixed position, and therefore they cannot move around, and they're not free to collide with each other.

This movement constantly happens even when they've evenly spread out, so like you saw in the animation, they continue to move.

And this movement doesn't require the addition of any additional energy.

So we don't need any heat.

We don't need any light, electricity.

We don't need any of these things.

The particles already have energy.

We don't need to add anything else.

And because of this, we call it a passive process because we don't need to add anything, any energy.

We're just relying on the energy that the particles already have in order for them to move randomly.

So diffusion is a passive process.

Let's carry out a check activity to check your understanding of what we've covered so far in today's lesson.

So what we have on the screen are three statements, A, B, and C.

And what we'd like you to do for each statement is to select one box.

So for example, for statement A, particles are free to move in liquids.

Are you sure it's right? Do you think it's right? Do you think it's wrong? Or, are you sure that it's wrong? So for each of the statements, just select one box.

You might want to pause the video while you do this, and then we'll have a look at the answers together.

Let's have a look at the answers.

So, A, particles are free to move in liquids.

That's right.

They are free to move.

If you remember through the animations we've seen, those particles can move over each other and around in the container.

Statement B, particles are free to move in solids.

That's right, it's definitely wrong.

In a solid, the particles are really close together, they're touching each other, they're in a regular arrangement, and they're not able to move at all.

In C, particles are free to move in gases.

That's right.

Just like a liquid, the particles are free to move.

Let's have a look at two more statements, D and E.

And just the same as before, I would like you to select one box for each of the statements D and E.

Again, you want to pause the video while you read through these and decide on your answer.

Let's have a look at the answers.

So D, movement of particles requires additional energy.

That's right, it's wrong.

The movement of particles doesn't require any additional energy as it's a passive process, and therefore the movement of particles is a passive process is correct.

So well done if you've got all of those statements right.

If you didn't, you might want to go back and have a look at the slides that we've covered and note down what the right answers are before moving on.

Now we're gonna have a look at real life situation to put this in a bit of context for you.

So deodorant is sprayed for one second.

So you can see we've got a deodorant can there.

Somebody's pressed the nozzle for one second, and you can see that the deodorant particles have come out from the can and into the air.

I'm gonna have a look now at what's happened after a minute.

So we only sprayed it for a second.

So we've stopped spraying.

We've put the lid back on, but you can see that those particles have started to move and spread out.

So what's happened is the particles are randomly moving in all different directions, possibly colliding with each other.

And what that's meant is that, over time, the particles have started to spread out.

And now I'm sure you can guess, but let's have a look at what it looks like after two minutes.

So you can see there that the particles have continued to move.

And through that random motion, it's a passive process.

It hasn't required any additional energy.

They are starting to spread out.

And I'm sure if we looked at this example in 20 minutes, in half an hour, that deodorant would've filled whatever room it was in.

And not only are the deodorant particles freely moving and colliding with each other, but also the air particles in the room are also randomly moving in all different directions and colliding with each other, and therefore the deodorant particles and the air particles will be moving past each other.

They'll be colliding with each other because they all are moving randomly.

Let's have a look at checking our understanding.

So the teacher sprays deodorant at the front of the classroom.

Which two of the following statements are true, A, B, C, or D? You might want to pause the video while you have a read through these and decide which two you're going to select as being true, and then we'll go through the answer together.

Let's have a look at the answers.

So B is true, the deodorant particles move past the air particles, and also the air particles move past the deodorant particles, and that's because the deodorant particles and the air particles are both gases.

They're both free to move.

They're moving in random directions, colliding with each other, and therefore all these particles will be passing each other and the deodorant particles will be spreading out.

A is not correct because the deodorant particles try to spread out so they have more space.

That's not true.

The deodorant particles are not alive and therefore they don't have wants and needs.

So for example, they don't want more space.

So they're not choosing to spread out.

It's just through the random motion that they do spread out.

C is also not correct 'cause the deodorant particles, they're not splitting into any more little bits so that they can mix with the air.

So well done if you've got both of those correct because that's a tricky question.

Let's have a look now at a practise task.

So you can see there in the picture that we've got a beaker of water, and we've added some dye to it.

So both the water and the dye are liquid.

And we haven't stirred these.

We've left it for the rest of the day.

And so what we'd like you to do is to write down and predict what you think will happen to the dye and the water, and explain why you think this will happen.

So draw on what we've gone through so far in today's lesson.

You will need to pause the video while you write down your answers to both of those questions, and then we'll go through the answers together.

So first of all, we asked you to predict what would happen to the dye and the water.

Well, the dye will spread through the water and cause it to change colour.

So you can see in the beaker there that, instead of having separate dye and water, it's all mixed together now and is one uniform colour, and that's what would happen if you left it over the day.

And the reason that that happens is because the water and the dye are both made of particles.

They're both liquids, and therefore they are constantly moving, and it's through that constant random motion that they will become mixed.

So well done if you've got those points.

So we've completed the first part of today's lesson and we're going to move on to the second part.

So the second part is about concentration and net movement.

Concentration is one of our key words, and it refers to the number of particles that you have in a volume of liquid or gas.

And so you can see on the screen here we've got two diagrams. On the left-hand side, we've got a higher substance that has a higher concentration.

And on the right-hand side, we've got a substance that's in a much lower concentration.

And so the more particles you have, the more concentrated the substance is.

If particles are more concentrated in one area as they are here on the screen on the left-hand side.

You can see we've got lots of particles, so we've got an area of high concentration and we've got an area where they're less concentrated.

So you can see on the right-hand side of the screen we've got an area of much lower concentration.

This creates what we call a concentration gradient.

So we've got a concentration gradient because we've got two different areas with different concentrations of a substance.

Let's check our understanding of what a concentration gradient is.

Concentration gradient is one of our key words today, and it's really important that we understand what it means.

So you need to select A, B, or C.

You might want to pause the video while you do this, and then we'll have a look at the answer together.

That's right, the answer is B.

It's a difference in concentration of a substance in an area.

So where you've got a particular substance that might be in high concentration in one area and a lower concentration in another area.

Well done if you've got that correct.

And if you didn't, please note down the right answer so that you know for next time.

Now we're gonna look at concentration and net movement.

We're gonna start by looking at what we've got on the screen.

So we've got an area of higher concentration on the left-hand side.

And on the right-hand side of the screen, we've got an area of much lower concentration.

And therefore when you've got areas that have a different concentration of particles or substances, you've got what's called a concentration gradient.

And so you can see we've put an arrow at the bottom to show the concentration gradient.

And we've added arrows to the particles to indicate that they're moving, and you can see that they're move in different directions.

So the particles are moving randomly in these different directions, and therefore that means, although we have a concentration gradient and the arrow is showing going from left to right, the particles actually move in both directions, and that's because the movement is random.

However, more particles move from the area of higher concentration to the area of lower concentration overall.

And therefore, when you've got more particles going from one direction than the others, it's what we call net movement.

So, overall, in this example, there's gonna be a net movement of particles from an area of higher concentration to an area of lower concentration, and that will lead to the particles being evenly spread over time.

Net movement is the movement down a concentration gradient where particles are moving, whether in an area of higher concentration to an area of lower concentration, and they're moving down their concentration gradient.

So you can see that in the animation below.

You can see the direction of the concentration gradient from higher to lower concentration, and you can see the overall net movement of the particles.

You can also see that the particles are moving randomly in all different directions, colliding with each other.

But overall, their net movement over time is from an area of higher to lower concentration, going down a concentration gradient.

After a while, particles become evenly mixed, and you can see that in the animation below.

It's really important to understand that the particles do continue to move.

So you can see on the screen they're moving randomly in all different directions.

They're colliding with each other, but there isn't a concentration gradient.

Because we don't have an area of higher and lower concentration, the particles are evenly mixed, and therefore not only do we not have a concentration gradient anymore, there's gonna be no further net movement.

So there's gonna be no overall movement from left to right or right to left, but the particles will continue to move, but there is no further net movement.

The net movement of particles down a concentration gradient is called diffusion.

And so we define diffusion as moving from an area of higher concentration to an area of lower concentration, and that means that the particles will become evenly mixed.

And you can see there that the net movement in this picture here is from the left-hand side of the screen where we've got particles in a higher concentration to the right-hand side of the screen, where they're in a much lower concentration, and therefore we've got an overall net movement from higher to a lower concentration area, and that is called diffusion.

Let's check our understanding of diffusion.

So which two of the following is needed for diffusion to take place? So you need to select two answers from A, B, C, and D.

You might wanna pause the video while you do this, and then we'll go through the answers together.

So we need the particles to be as a liquid or a gas in order for diffusion to take place because it involves the movement of particles.

So if the particle's not liquid or they're not in the gas state, then they're not going to be able to move and diffusion won't be able to take place.

And we also need a concentration gradient.

We need a difference in the amount of the substance between areas in order to have a concentration gradient and for those particles to move from a higher to a lower concentration in order for diffusion to take place.

Well done if you've got both of those correct.

C is not correct.

We don't need extra energy.

Remember diffusion is a passive process.

We don't need to add any heat or anything else in terms of energy in order for this to take place, and we don't need a living organism.

We saw earlier the deodorant can, the deodorant is not living, and therefore we don't need a living organism in order for diffusion to take place.

So now let's have a look at what happens when the particles are evenly mixed.

So you need to select the correct answer from A, B, C, and D.

Again, you'll want to pause the video while you choose your answer, and then we can discuss the right answer.

So what happens when particles are evenly mixed? Well, the particles continue to move, but there is no net movement.

So we know the A is wrong because, the particles, they don't get any slower.

They don't stop moving.

They continue in their random motion.

C is not correct because the particles, there is no overall net movement because they're already evenly mixed.

So they are not moving overall from one area to another.

And D is not correct because diffusion doesn't continue to take place.

If you remember, diffusion is moving from an area of higher to lower concentration.

And if the particles are evenly mixed, then we don't have that concentration gradient, so there's no diffusion to take place.

So well done if you got that correct.

Now let's have a look at a practise task.

So Sofia and Jacob are talking about making iced tea using cold water.

You can see in the picture there we've got a cup and a tea bag.

So Sofia thinks, "I think you can make iced tea by leaving a teabag in cold water." And Jacob says, "No, you need to use hot water and stir, or you will just end up with water." So who do you think is right? So who do you agree with? I would like you to explain your answer, drawing on what we've covered during today's lesson.

You will need to pause the video while you write down your answer.

Let's have a look at the answer.

So Sofia is correct, you can make ice tea by using a teabag and cold water, and that's because the tea is made up of particles, and the particles are constantly moving, and they don't need any extra energy by being heated up.

So you don't need hot water.

And obviously, we've got a concentration gradient between the teabag where the tea particles are in a really high concentration, and you've got the water where they're in a much lower concentration.

And therefore you're gonna get diffusion taking place where the tea particles move down the concentration gradient from inside the teabag, we're in the higher concentration, into the water, where they're in a much lower concentration.

And over time, the tea particles will become evenly mixed in the water.

So well done if you've got that correct.

Now we're going to move on to the third part of today's lesson, which is about diffusion in cells.

Let's have a look at what we've got on the screen.

So we can see there we've got a cell and we've labelled the cell cytoplasm.

Remember the cell cytoplasm is where the cells chemical reactions take place, and it's full of different substances.

So some examples of substances are water, oxygen, sugar, and carbon dioxide, and all of these substances are made up of particles.

We know that the cell cytoplasm contains lots of different substances.

Those substances are made up of particles, and those particles are constantly moving.

and the movement is in all directions and random.

And therefore you get diffusion taking place of different substances within the cell cytoplasm.

Now we're gonna do a check activity to check your understanding.

So we've got the cell cytoplasm is made up of particles.

I want you to imagine that you can see those particles, and I would like you to select a diagram and description that best matches what you would see.

So we've got A, B, C, and D.

You might want to pause the video while you choose your answer.

That's right, you would see B.

If we could have a detailed look at the cytoplasm, B is what you would see.

So we've got particles close together, but moving freely.

So diffusion is really important in cells, particularly in making sure that the parts of the cells get the substances that they need.

So as an example, if we have a look at the mitochondria, mitochondria need a really good supply of sugar and oxygen, and they need both of these substances in order to carry out life process cellular respiration.

And so particles of sugar and oxygen reach the mitochondria by diffusing through the cytoplasm.

Now let's do a check activity.

So is it true or false that substances in the cell cytoplasm move by diffusion? And then I'd like you to think about why you chose that particular answer.

So justify your answer by selecting statements A or B to support your answer of true or false.

You might want to pause the video while you read through all of this and select the right answers.

That's right, it's true.

Substances in the cell cytoplasm move by diffusion.

So they move from areas of high concentration to areas of low concentration, and this is because the substances are constantly moving in all directions, and it's not because the particles or the cell are choosing to move from one part of the cell to another.

Well done if you got that correct.

Now, let's have a look at a practise task.

So the mitochondria need a good supply of sugar.

I'd like you to explain how the particles of sugar get to the mitochondria, drawing on what we've covered in this lesson.

You will need to pause the video while you write your answer, and then we'll go through the answer together.

Now let's have a look at the answer.

So we're explaining how the particles of sugar get to the mitochondria, so the mitochondria cell organelle in the cytoplasm.

So those particles of sugar, which we've represented as blue circles, are constantly moving in random directions, and they don't need any energy to do this.

We don't need any extra energy, I should say, to do this.

And so, overall, you can see the pink arrow show the overall net movement.

We're getting a net movement of particles from where they're in an area of higher concentration near the cell membrane to where they're in a much lower concentration towards the centre of the cytoplasm.

And so it's through this movement that those sugar particles will diffuse through the cytoplasm and they will reach the mitochondria, and then the mitochondria can use those in cellular respiration.

So well done if you've got that correct.

We've almost reached the end of today's lesson.

Let's go through a summary to make sure that we've got the key points.

So first of all, all substances are made of particles, and we know that those particles can be arranged as a solid, a liquid, or a gas.

And we know that where they are a liquid or a gas, that those particles are able to move and that they move randomly.

And this random movement causes a process of diffusion, and we get diffusion where we have a concentration gradient, so where particles are in a higher concentration compared to an area where they're in a lower concentration, and therefore we get net movement of particles from the higher to the lower area of concentration.

And we refer to that as moving down a concentration gradient.

We know that diffusion is a passive process, so it does not require any additional energy other than what the particles have themselves.

We don't need to apply any heat or light, for example.

We also know that cells in the cytoplasm have many dissolved substances within them, and that those substances move around the cytoplasm because of diffusion.

And you can see the diagram there.

We've got the blue circles representing a substance, it could be sugar, and they're going to move from where they're in a high concentration to where they're in a lower concentration just through a random movement so that they become evenly distributed.

I hope that you've enjoyed today's lesson.

I'll see you next time.

There is an exit quiz, and I would really encourage you to have a go at that to check that you've definitely understood all the points from today's lesson.

See you next time.