Hi, I'm Mrs. Hudson, and today, I'm really looking forward to teaching you a lesson called diffusion through a permeable material.

This is also going to include some practical work and it's a science lesson, which comes under the unit called Diffusion.

The outcome of today's lesson is that I can explain observations of diffusion through jelly cubes, a permeable material.

So, today, we're going to be looking at diffusion and how that happens through a permeable material.

And the permeable material we're going to be looking at is jelly cubes.

There will be some keywords during today's lesson that will help us to understand lots of the material, and these are the keywords, diffusion, net movement, permeable, variable, and prediction.

So, let's have a look at what those words mean.

Diffusion is the net movement of particles of a substance down a concentration gradient.

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

And the key thing there, it's the overall movement, because particles move randomly and in all directions.

But the net movement is the overall movement.

Permeable, a material is permeable if particles of liquid are able to move through it.

And this is very important in biology, because cell membranes are semi-permeable, which means that they allow some substances to move through them.

Variable.

In a science experiment, a variable is a factor that can be changed, kept the same, or measured.

Prediction.

A scientific prediction is a testable statement about a possible outcome of an experiment.

Today's lesson will have the following outline.

So, the first part of the lesson, we'll be going to looking at diffusion into a jelly cube and just trying to describe how that happens.

And then, we're going to look at changing some variables in the second part of the lesson.

So, factors that might affect how diffusion can occur across that jelly cube.

All substances are made up of particles.

And when a substance is in the liquid or gas state, the particles move all the time in random directions.

So, if this is a particle diagram of a solid, you can see that the particles have a regular arrangement and that they are touching each other and they are unable to move.

Whereas in a liquid and in a gas, you can see that the particles are able to move.

In a liquid, they can move around each other and they take the shape of the container.

Whereas in a gas, the particles move randomly and in all directions.

But we would say that liquid and gases are fluid, because their particles are able to move.

The constant movement of particles causes diffusion.

When there is a concentration gradient, more particles move.

And this picture here is showing you an area where there is a high concentration, and that's on the left-hand side of this box.

There are more particles in that area.

And then, there's a lower concentration in the right-hand side of the box, because there are fewer particles in that area.

And therefore, the purple line is showing us the concentration gradient, which is moving from the high concentration down to the lower concentration.

So, there is a net movement down the concentration gradient and net movement from the higher concentration to the lower concentration.

That doesn't mean that there aren't particles moving from the lower to the higher concentration, because remember that particles are moving randomly and in all directions.

It just means that overall, there are more particles moving from the higher concentration to the lower concentration.

And the key thing here is that when there is a concentration gradient, more particles will move and they move from the area of higher concentration to the area of lower concentration.

This is called net movement.

Time to have a quick check for our understanding.

So, the first question I'd like you to answer is this, what causes diffusion? A, the concentration of particles.

B, the movement of particles.

Or, C, the substance of particles.

Hopefully here you ticked B, diffusion is caused by the movement of particles.

A, the concentration of particles, the concentration is what leads to the concentration gradient, but it doesn't cause diffusion.

Diffusion is a passive process and it happens because particles are moving randomly and in all directions.

Now, let's have a go at this question.

The diffusion of particles down a concentration gradient is called, A, concentration movement, B, gradient movement, or, C, net movement.

Hopefully for this one, we wrote the net movement, C.

Well done if you got that right.

Remember that net movement is the overall movement of particles, and this happens because particles are moving from a higher concentration to a lower concentration down a concentration gradient in diffusion.

Now, let's look at diffusion into a jelly cube.

So, some materials are permeable.

Remember, permeable means that liquids are able to move through the permeable material.

A cube of jelly is a permeable material, so that picture there is showing you a cube of jelly and it is permeable.

So, that means that liquids are able to move through the surface of that jelly cube and into the jelly cube.

Therefore, if we put the jelly in a liquid, particles of the liquid will diffuse into the jelly, just like these lines are representing here.

And that happens because the concentration of water is higher on the outside of the jelly cube.

So, there's a concentration gradient.

So, particles move randomly and passively down a concentration gradient into the jelly cube.

We can put a cube of coloured jelly into acid and remember that acid is a liquid, so it would behave similarly to the way that jelly would behave if it was placed into water.

When we do put jelly into acid, particles of acid diffuse into the permeable jelly, and that happens because there's a higher concentration of acid outside of the jelly cube.

So, therefore, there's a concentration gradient, and the acid particles move from a high concentration to a low concentration, which would be inside the jelly cube.

The particles of acid then cause the jelly cube to turn colourless.

What do you think you will observe when we watch a video putting jelly into acid? And how will the appearance of the jelly cube change over time? We're going to watch a demonstration now to observe exactly what does happen when we place this jelly cube into the acid.

So, again, you need to use those pieces of information to have a think about what you think you will observe and how will the appearance of the jelly cube change over time.

Let's have a look and watch the video.

So, we're going to be looking at diffusion of acid into a coloured jelly cube.

So, you can see the jelly cube is being placed into the acid now.

And initially, there's a very high concentration of acid particles outside of the jelly cube and a low concentration of acid particles on the inside of the jelly cube.

So, therefore, there's a net movement of acid particles from outside of the jelly cube towards the inside of the jelly cube.

Now, initially, this net movement will just occur across the surfaces of the jelly cube and down that concentration gradient.

And you can see now that the outer surfaces of the jelly cube has started to become decolorized, because the acid particles have diffused through the surface into the jelly cube.

However, over time, what will happen is that net movement will continue to occur from the outer surfaces of the jelly cube towards the centre of the jelly cube, where there is still a concentration gradient.

And now, the video has been sped up, and we can see that the decolorization is occurring from the outer surfaces towards the centre.

And this is because diffusion is occurring now from the outer surfaces of the cube right through into the middle of the cube.

And again, that's going down a concentration gradient from a high concentration to a low concentration.

And we can see now that the cube is almost becoming completely colourless.

And again, this is all happening, because of diffusion from a high concentration to a low concentration, the net movement of particles down a concentration gradient.

And now, look at that jelly cube.

It is totally colourless, because the acid has diffused throughout the whole of that jelly cube right to the centre.

Right.

Let's do another check for understanding.

So, here, particles of acid are able to move into the jelly, because it is, A, a cube, B, a material, C, diffuse, or, D, permeable.

Now, hopefully you put here D, permeable.

The jelly cube is permeable, which is what allows acid, which is a liquid, to move and diffuse into the jelly cube.

Time for us to have a go now at our first task.

So, the photographs here show what happens when a coloured jelly cube is placed in acid.

Your job is to write an explanation for why the appearance of the cube changes, and you can use the following words in your explanation.

Particles, permeable, net movement, concentration gradient, and diffusion.

I'm sure you're going to do a really fantastic job of this.

So, pause the video now, and then press play again when you are ready for me to go through the answers.

Let's check how you've done.

So, particles of acid can move into the cube, because it is permeable.

There is a high concentration of acid particles outside the cube.

The net movement of particles of acid is down the concentration gradient from the outside to the inside of the cube.

Particles of acid move into the cube due to diffusion from each surface of the cube towards the middle of it.

The particles of acid cause the jelly to turn colourless, starting from each surface of the cube, then moving inwards towards the middle.

Now, you might not have everything that's written down here, but you can pause a video now to add anything into your answer and to make your answer just a little bit better if you need to.

Brilliant job.

We're now onto the second part of our lesson, which is about changing variables.

Let's get going.

In a science experiment, a variable is a factor that can be changed, kept the same, or measured.

And there are three different types of variables that you need to know about.

The first one is the independent variable.

The second one is the dependent variable.

And the third one are the control variables.

Now, the independent and dependent variable are always only one factor, whereas the control variables sometimes could be more than one factor.

So, let's have a look at what those things actually mean.

The independent variable is the factor that is being changed in that experiment.

The dependent variable is the factor that is being measured, and the control variables are the factor that is kept the same.

The reason we have to have control variables are that only the change in the independent variable can affect the results.

So, we don't want anything else in that practical to affect the results.

So, we have to keep everything other than the independent variable, exactly the same.

And those are called the control variables.

Let's just quickly check our understanding of that.

So, match each type of variable to its correct description.

So, you have the three variables, independent, dependent, and control.

And then, A, B, and C.

A factor that's kept the same is A.

A factor that's being changed is B.

And the factor that's being measured is C.

So, match each one up really quickly, and then we'll go through the answer.

Okay, so let's have a look.

The independent variable is B.

That's the factor that's being changed.

The dependent variable is the factor that is being measured, which is C.

And the control variable is the factor that you are keeping the same.

Excellent if you remember that.

Really great job.

Before we do a science experiment, we can make a scientific prediction.

Now, a scientific prediction is a testable statement about a possible outcome of an experiment.

For example, predicting the effect that a change to the independent variable will have on the dependent variable.

So, if you change a factor in an investigation, what will happen to the factor that you measure and you are making a prediction about that change.

A scientific prediction can always be tested using an experiment.

So, if you are making a prediction, you should always be able to test that prediction.

So, let's just check that we understand that.

So, which statement is a testable scientific prediction? A, diffusion is caused by moving particles.

B, the time taken for the jelly cube to turn colourless in acid was 30 minutes, 45 seconds.

Or, C, using stronger acid will make the jelly cube turn colourless faster.

So, which one of those is a testable scientific prediction? So, hopefully here we wrote C.

That is the only testable scientific prediction.

A is just an explanation and B is an observation, whereas C is a testable scientific prediction.

Really well done if you got that right.

When investigating the diffusion of acid into a coloured jelly cube, a variable we can change is temperature.

So, here, if we had a test tube that was filled with some acid and had a jelly cube in, we could have the temperature 20 degrees, at 40 degrees, and at 60 degrees.

So, the factor we are changing, the variable we are changing is the temperature.

So, here, we've got the three variables.

Again, the independent, the dependent, and the control variable.

So, let's think back to what each of those mean.

The independent variable is the thing that you are changing.

So, in this case, the factor we are changing is the temperature of the acid.

The dependent variable is the factor that you are measuring.

If we are trying to investigate diffusion of acid, we're going to look at the time taken to decolorize each cube, because that effectively is saying what is the rate of diffusion or how quickly is diffusion happening? And to make sure that the only thing that is affecting the results, we have to make sure that the size of the cubes remains the same, because the size of the cubes could also affect diffusion.

We don't have to heat a liquid for diffusion to take place.

So, if we look at this particle diagram of a liquid here, we can see that the particles take the shape of the container, but also that they are able to move around each other.

So, diffusion happens all the time in a liquid, because the particles are constantly moving.

They are randomly moving around each other.

But increasing the temperature increases the speed of which the particles move.

Remember, if you heat particles, they gain kinetic energy, and so they are moving around at greater speeds.

That means that diffusion can happen faster if you increase the temperature.

But you don't have to heat a liquid for diffusion to take place.

Let's just quickly check our understanding of that.

So, which scientific prediction is most likely to be correct here? So, we've got three different test tubes of acid with jelly cubes in at 20 degrees, 40 degrees, and 60 degrees.

A, at higher temperatures, the time taken to decolorize the cube will be longer.

B, at higher temperatures, the time taken to decolorize the cube will be shorter.

Or, C, increasing the temperature will have no effect on the time taken to decolorize the cube.

Hopefully here, we recognise that at higher temperatures, the time taken to decolorize the tube will be shorter, and that's because diffusion will happen more quickly, because there's a higher temperature.

Okay, so let's actually look at this in action.

So, our scientific prediction is at higher temperatures, the time taken to decolorize the cube will be shorter.

And remember, the decolorization of the cube is representing how quickly diffusion is taking place.

So, watch this demonstration and let's observe what happens.

Did the observations from the experiment support our prediction? So, did the higher temperature cause the cube to decolorize in a shorter amount of time? Let's watch the video and have a look.

So, we are going to be looking at diffusion of acid into a coloured jelly cube again, but this time, with different temperatures.

So, you can see the three jelly cubes have been placed inside of the acid and the test tubes are in water, and that water would've been left at the specific temperature.

So, the acid will be the same temperature as what it says underneath.

And you can see now that the acid is diffusing across the surface, it's going down that concentration gradient.

And if you look at the 60 degree test tube, you can see that that one is decolorizing much faster.

And that's because diffusion is happening now through the jelly cube at a much greater rate, because the particles are moving much faster because it's an increased temperature.

So, now, this cube in the 60 degree tube has already decolorized.

That was the fastest to decolorize.

40 degrees is also decolorizing now.

Diffusion is still taking place in both 40 degrees and 20 degrees.

But you can see over time, the cubes in or the cube in 40 degrees has become decolorized.

And now, we're just left with the cube at 20 degrees.

That cube is now also decolorized.

Okay, let's have another check of our understanding.

So, we've got a table here that has the temperature, which is 20, 40, and 60 degrees, and then the time taken to decolorize the cube.

So, at 20 degrees, it was 602 seconds.

At 40 degrees, 566 seconds.

And 60 degrees, 380 seconds.

So, your job is to say which statement describes the observations from the experiment? A, at higher temperatures, the time taken to decolorize the cube was longer.

B, at higher temperatures, the time taken to decolorize the cube was shorter.

Or, C, at higher temperatures, the time taken to decolorize the cube was the same as the lower temperatures.

You decide which one of those is correct.

And hopefully here, you've gone with B.

So, at the higher temperature, the time taken to decolorize the cube was shorter.

And remember, this happens, because diffusion is taking place faster when you increase the temperature, the particles are moving around quicker and therefore, diffusion takes place faster.

Next question.

This is a very similar question, but you've just got to be very careful with the words that are in the questions.

So, which statement explains the observations from the experiment? And A here, at higher temperatures, particles of acid diffuse to the centre of the cube faster.

B, at higher temperatures, particles of acid diffuse to the centre of the cube slower.

C, at higher temperatures, particles of acid diffuse to the centre of the cube at the same rate as the lower temperature.

So, which one of those is correct? Now, hopefully this time, you recognise it was A.

So, we have used the word faster rather than shorter.

So, diffusion is happening faster, but also we're talking here about the diffusion of particles to the centre of the cube.

So, initially, the particles will diffuse from the acid through the surface of the cube, and then they would start to diffuse through the actual cube itself from the outer surface of the cube into the centre of the cube.

And that happens faster if you have a higher temperature.

So, well done if you got that correct.

It's time now to have a go at our second task.

So, when investigating the diffusion of acid into a coloured jelly cube, a variable we can change is the size of the cube.

And you can see here three pictures where there's a width of one centimetre, which is a slightly smaller cube, a width of 1.

5 centimetres, which is a more middle-sized cube.

And then, the width of two centimetres gives you the largest cube.

The first question is to identify the independent variable, the dependent variable, and the control variable.

And then, the second question is write a scientific prediction for this experiment.

So, remember, a prediction has to be testable, and it's how the independent variable is going to change the dependent variable.

So, pause the video now, have a go.

I'm sure we're gonna do a fantastic job, and then press play when you're ready for me to go through the answers.

Let's have a look.

So, for the first task, identifying the variables, the independent variable, the fact that you changed was the size of the cubes or the width of the cubes.

The dependent variable, the fact that you measure, was the time taken to decolorize each cube.

And the control variable, we have to think about something else other than the size of the cubes that will affect the results or the rate of diffusion, and that would be the temperature of the acid.

So, well done if you managed to get those correct.

And then, write a scientific prediction for this experiment.

You should have something along the lines of the time taken to decolorize the cube will be longer for a cube with a larger width.

You could have also said that the time taken to decolorize the cube will be shorter for a cube with a shorter width.

Now, let's have a look at the second part of task B.

So, watch the demonstration to observe what happens.

So, we're going to watch a video and look at what happens.

And you are going to answer the following questions.

Did the observations from the experiment support your prediction? And number four, how would you explain the observations from the experiment? And remember, if you are explaining something, you are saying why it happens.

So, we're going to watch a video now and you are going to answer those questions.

So, you need to now answer part three and four of task B.

You might want to pause the video now to give yourself time to answer the questions in task B, part three and four.

If you need to go back into the slide deck to have a look at what those questions are, I think that would be really useful.

But then press play when you are ready for me to go through the answers.

Let's see how we did with those questions about that practical.

So, question three, if you predicted that the time taken to decolorize the cube will be longer for a cube with a larger width, then the observation did support the prediction.

Number four, how would you explain that observation? So, the time taken to decolorize the cube with a larger width is longer, because particles of acid have to diffuse further from the surfaces of the cube to reach the middle of it.

So, therefore, diffusion will take longer, because in a cube with a shorter width, there is less distance for the particles to have to diffuse to get to the centre of the cube.

Whereas a cube with a much larger width, there's a much greater distance to the middle of the cube, and therefore diffusion will take much longer.

You've done a fantastic job today.

If you need to pause the video to add anything into your answers, please do.

But let's now go on and summarise everything that we have learned.

So, in summary, particles of liquids are able to move through permeable materials by diffusion.

And remember that permeable means that liquids are able to pass through.

The net movement of particles of liquid is down the concentration gradient from the outside of the permeable material to the inside of it.

A scientific prediction is a testable statement about a possible outcome of an experiment.

And finally, we can make a prediction about the effect that a change to the independent variable, for example, the cube size, will have on the dependent variable, for example, the time it takes for decolonization to occur in an experiment.

Well done today.

You've done an absolutely brilliant job and I look forward to seeing you next time.