Lesson video

- Hello and welcome to today's Oak Academy Science session.

My name is Mrs. Bowes, and I'm really looking forward to teaching you today.

To make sure that you're ready to go, have a pen and some paper, and then we can get going.

The title of today's lesson is, Microscopes, magnification and resolution.

And the outcome is to describe and compare the images produced by light and electron microscopes.

This is a science lesson and it comes in the key stage four topic called Cell Biology.

If you need to pause a video now to write down the title please do and then press play so we can begin.

The keywords that will help us to understand today's lesson are micrographs.

And micrographs are images produced by microscopes.

A specimen is something that is viewed through a microscope.

A micrometre is a unit of measurement that is 1000th of a millimetre and a nanometer is a unit of measurement that is 1000000th of a metre.

The outline of today's lesson is as follows.

The first thing that we're going to look at is the difference between magnification and resolution.

Then we're going to talk about light microscopes and how they produce images.

We will then look at electron microscopes and how they produce images.

And then finally, we are going to compare light and electron microscopes.

But to begin with, let's look at microscopes and the difference between magnification and resolution.

So this picture here is showing us a microscope.

The first microscope was thought to be made in around 1600.

We're not exactly sure of the date but we believe it was around 1600.

So you might have used microscopes before.

What are microscopes used for? We think we know? Microscopes are used to magnify images that are too small to see with our eyes.

And the keyword there is magnify.

They magnify images that we wouldn't normally be able to see with our naked eye.

These images here show cells that are viewed underneath the microscope.

Now have you got any idea what you think these cells might be? Well, the first images is showing some bacteria cells, they are E.

coli cells.

And then the second image is showing as a plant.

It's a water weed plant and they're the cells viewed under a microscope.

Images produced from microscopes are called micrographs.

So what we need to know from this slide is that, micrographs are the images that microscopes produce.

Hey, can you read the time on this clock which is inside of that red rectangle in the picture? Some of you might be able to, you might have a very good sight.

I find that quite difficult to see.

What if I magnified that image? So I've magnified it now.

Is it easier for you to see the time? I think so.

I think there's quite clearly 10:57.

It wasn't so obvious before the image had been magnified.

Microscopes, magnify objects that are two small to see with the naked eye.

So this picture here is showing you a leaf and without a microscope we can't see the cells of that leaf.

But if we magnify it using a microscope then we can view the individual cells and some of the sub-cellular features within the plant cells.

Now looking at these micrographs, what's the difference? And I'm gonna give you a clue.

All three of these pictures are of the same specimen.

They're the same thing.

But what is different about them? They've got different magnifications.

Magnification is where you magnify an object and each of those images has got a different magnification.

Resolution is how clearly two points can be distinguished from each other.

So if we look at these two pictures here, one of them looks a little bit blurry and the other one you can see the cells in more detail, they're more clear.

So the blurry picture we would say, has a low resolution.

It's not very clear.

The image isn't very detailed.

Whereas the second picture is a high resolution.

You can see the cells, they're clearer to see and you can see more detail within them.

If you increase the resolution of an image it allows you to see more clearly.

So just to summarise the difference again between magnification and resolution, magnification magnifies an object.

So if I wanted to magnify this image, it would look that.

Resolution allows you to see images clearly in more detail.

So if you had a magnified image like that, but it's a bit blurry and you can't see the details, you need to increase the resolution, so that you can see the detail within that image.

Right.

We should be ready now to answer a few questions.

So just give it your absolute best go.

Please don't worry if you get anything wrong.

So the first question is, images produced from microscopes are called, A, micro pictures, B, microscopic photos, or C, micrographs.

This is C, they are called micrographs.

If you want to magnify an image, what must you change? A, increase the magnification.

B, decrease the magnification, or C, increase the resolution.

And this one, we need to, A, increase the magnification.

Well done if you've got that.

Now next question is true or false.

Increasing the resolution shows images more clearly in detail.

True or false, and then justify your answer.

So A, increasing the magnification magnifies the image and shows it more clearly, or B, To view this blurry image more clearly you would increase the resolution.

Is it first, is it true or false? This is true.

And the reason why it's true is B, because if you've got that blurry image you need to increase the resolution to make it more clear and see the details.

Amazing if you've got that.

Well done.

We are now ready to move on to our first task.

So you need to look at these micrographs and identify if the magnification or resolution has increased.

So one example, it will be the resolution that's increased and then the other example it will be the magnification that has increased.

Pause the video now and then press play when you're ready for me to go through the answers.

Okay.

So for i, you can see we've got two pretty clear images but that the first image there are a lot more cells within the same area.

So for i, you should have that, the magnification has increased, you have magnified that image.

Whereas in the second example, you've gone from quite a blurry picture to a picture that's been seen.

You can see a more detail that's very clear.

So in ii, the resolution has been increased.

So mark your work.

Absolutely amazing if you manage to identify those.

We've got some more questions next for you to have a go at.

So describe what you could do to improve the micrograph for each image.

So here you need to say whether you need to increase the magnification, or increase the resolution and you need to write in full sentences.

So pause the video and have a go.

Okay, so for i, you can see that that image is quite blurry.

So what we would need to do to see it in more detail is that, the resolution needs increasing to see the micrograph in more detail.

Whereas for ii, you can see the cells but they're just not magnified enough.

You need to be able to get higher magnification to get in and see them.

So therefore the answer would be the magnification needs increasing to magnify the cells.

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

But we are going to carry on now with the rest of the lesson.

Amazing work.

We now know the difference between magnification and resolution, and we're going to move on to talk about how light microscopes produce images.

The first microscopes to be used were light microscopes, and these are the microscopes that you found in schools.

So if you've ever used a microscope before is probably a light microscope.

And how do they work? Well, at the bottom of the microscope there is a light source, and this shines up through the sample.

Now the sample is held in place on the stage with those little clips and the sample's usually held on a glass slide and that's got the live specimen on it.

You can use specimens that are alive in a light microscope.

So you've got the light source that shines up through the specimen, and then you've got two sets of lenses on a light microscope.

The top lenses are called the eyepiece lenses and then they are the ones that are black on this diagram.

And then the silver lenses are called the objective lenses.

And both of those together magnify the image.

A light microscope can magnify images up to 2000 times.

So these two pictures here are showing you two examples of cells that are viewed under a light microscope.

And because they can be magnified up to 2000 times you can see larger sub-cellular structures within the cells.

So the first slide is shown you a nucleus within those cells, an animal cell, and then the second picture is shown you a plant cell where you can see the chloroplasts.

Nucleus and chloroplasts are larger sub-cellular structures.

Light microscopes allow you to view larger sub-cellular structures.

The resolution of a light microscope is roughly 0.

2 micrometres, or we could say that as 200 nanometers.

This means that they cannot distinguish two points that are closer than 200 nanometers together.

Now this is one of the limitations of the light microscope.

As a result, you can't see smaller sub-cellular structures such as the ribosomes.

So you are able to see the nucleus and the chloroplasts, but you can't see ribosomes.

You also can't see inside of sub-cellular structures because the resolution is just not high enough.

Right.

Let's see how much of that we have understood.

Again, just give it your best go.

So first question.

What travels up through the sample in a light microscope? A, electrons, B, lenses, or C, light.

This is C, it is the light.

Comes with the name really light microscope.

True or false? Light microscopes can view live samples, and then justify your answer.

A, only dead samples can be used as light damage as the samples, or B, live samples can be used as light does not damage the sample.

This is true.

We can use live samples of light microscopes and the reason being, the light does not damage the samples at all.

Next one, which part of the microscope magnifies the sample in a light microscope? A, the light source.

B, the lenses, or C, the stage.

This is B, the lenses.

Remember there are two different lenses on the light microscope, the objective lens and the eyepiece lens, and those are what magnify the image.

Amazing job if you're getting these right, really, really good work.

How many times can a light microscope magnify a sample? A, 200, B, 2000, or C, two million.

This is B.

2000 times you can magnify an image on a light microscope.

What is the resolution of a light microscope? And be careful here because I've mixed the units up.

Some are in micrometres, some are in nanometers.

So A, is not 0.

2 micrometres, B, is 200 micrometres, and C, is 0.

2 nanometers.

Have you remembered this one? This is A, 0.

2 micrometres.

So if you've got C, just check micrometres, not nanometers, it would be 200 nanometers.

Which sub-cellular structure can you not view with a light microscope? A, chloroplasts, B, ribosomes, or C, nucleus? This is B, you cannot view ribosomes, they're too small to view with a light microscope.

Absolutely brilliant.

We are now ready to move on to task two.

So your job is to write sentences and label this diagram of a light microscope to describe how it magnifies a sample.

And you've got some keywords to help you.

So you should use slide, lenses, light source, magnify, and specimen.

Pause the video now give it your best go and then press play.

And I'll be here to go through the answers with you.

Right.

Hopefully we had a really good go at that.

So we'll start with the light source.

The light source is at the bottom, so you should have that labelled there.

And it shines light up through the sample.

And then the second line is pointing towards the lenses.

So the lenses magnify the image.

And then we've got the slide which holds the live specimen in to be viewed.

So you might have also labelled the specimen which is the circular bit within the slide with the little green blobs on it.

So if you need to pause the video to jot anything down, add any improvements, please do, and we will continue.

So next questions.

Answer the following questions in full sentences.

For ii, please make sure that you use the right units.

So check the units for that one.

Pause the video and then when you're done, you can pick back up again, I'll go through the answers.

Right then let's get going.

So for i, you should have had the maximum magnification of a light microscope is 2000 times.

For ii, light microscopes have a resolution of 0.

2 micrometres, or you could have written 200 nanometers.

iii, which sub-cellular structures can be viewed with a light microscope? Light microscopes can view larger sub-cellular structures such as the nucleus and the chloroplasts.

Really great work.

If you need to pause a video now to add anything in please do and we will keep going with the rest of the lesson.

Right.

So we now know how light microscopes work and we're going to now do the same thing for electron microscopes and how they produce images.

So electron microscopes are different to light microscopes because rather than using light to view the sample they instead fire electrons at samples to produce micrographs.

And they were first used in 1931.

So they were used a lot later than the first light microscope which we said was around 1600.

They were first used in 1931, and the person who invented the first electron microscope actually won the Nobel Prize, because it was such a great discovery in the scientific world.

And so this here has shown you a picture of an electron microscope and electrons are fired at that sample to produce the micrograph.

Now specimens can become damaged by those electron beams and therefore only dead specimens can be viewed.

So we can't use live specimens with an electron microscope, only dead specimens.

And those specimens have to be really carefully prepared before that they can go into the electron microscope.

And this does limit the use of electron microscopes because you can't use samples that are alive.

Now, electron microscopes can magnify images by one to 50 million times and also the resolution is less than one nanometer.

Sub-cellular structures can be seen such as ribosomes.

So in comparison to light microscopes they've got a much higher magnification and a much higher resolution.

And that means, that you can see smaller sub-cellular structures like the ribosomes that we couldn't see with our light microscope.

So here this is electron micrograph and you can see here the inside of a mitochondria, but it doesn't just allow you to see smaller sub-cellular structures.

It allows you to see inside other sub-cellular structures like this mitochondria.

And then this electron micrograph is showing you a nuclear envelope.

So it's part of the nucleus and it you are able to see the cell in much more detail than you otherwise could have done with a light micrograph.

Now, electron microscopes allowed scientists to explore smaller parts of the cell and inside sub-cellular structures.

And we've used this information to understand more about cellular processes that we just weren't able to do with light microscopes alone.

So now for example, this is a really lovely picture, it's a 3D graphic of a human cell and we would never have been able to produce images like this without the invention of electron microscopes because we simply wouldn't have known that some structures existed, or what the insides of those structures look like.

And being able to see what the structures look like, has given us a better idea of the cellular processes that are going on inside of cells.

Right.

So now we should be able to answer some questions about electron microscopes.

So the first one, what does an electron microscope fire at samples? A, light, B, electron beams, or C, protons.

Again, this one's in the name B, electron beams are fired at the sample.

What is the magnification of an electron microscope? A, 10 to 100,000, B, one to 50 million, or C, 100 to 200,000.

This is the biggest one.

This is B, one to 50 million times the size of that cell, which is huge.

Next question.

What is the resolution of an electron microscope? Watch the units again here for this one.

A, one micrometre, B, a 100 nanometers, or C, one nanometer.

This is C, one nanometer.

Which statement is true for specimens when using electron microscopes? A, the specimen is dead.

B, the specimen is alive, or C, the specimen can either be dead or alive.

This is A, the specimen has to be dead for an electron microscope to be used.

Which sub-cellular structure did light microscopes enable us to visualise? A, the cell wall, B, the nucleus, or C, the ribosomes.

Okay, this is C, the ribosomes.

They were too small to see with the light microscope.

Right.

We are ready now to move on to task three.

The first part of this is to complete the table about electron microscopes.

So you just need to say what the source of the image is.

By that I mean how do we visualise that image and the light microscope, it was by shining a light through the sample.

What happens to this sample with an electron microscope? What's the magnification or the highest magnification? What's the highest resolution and the specimen? Does the specimen have to be alive or dead? And then B, describe how electron microscopes have enhanced our understanding of cell structures and processes.

I'm sure you're gonna do amazing job of this.

Pause the video now and then press play and I will go through the answers.

Okay, let's see how you did.

So the source of the image and an electron microscope is, electrons are fired at the sample.

The magnification is one to 50 million times, the resolution is one nanometer and the specimen has to be dead.

Really great job if you managed to remember all of that.

And then B, you should have written that, electron microscopes allowed scientists to see smaller sub-cellular structures such as ribosomes.

It's also allowed them to see inside other organelles which helped us to understand cellular.

If you need to pause the video to add in a few corrections or a little bit of extra detail into your answer, please do.

Really great job so far though, well done.

Right.

We are now going onto our final phase of the lesson.

We know what like microscopes are, we know what electron microscopes are.

Now let's compare the two together.

So, all of the sides that are coming up now are gonna have light microscope and electron microscope and it's gonna compare a particular feature of that microscope.

So the first thing we're gonna compare is the source of the image.

The inner light microscope, a light is shone up through the specimen, so that you can see that specimen.

Whereas an electron microscope, electrons are fired at the specimen.

Magnification and a light microscope, the magnification can go up to 2000, which enables you to see the outline of cells but also some sub-cellular structures like the nucleus or the chloroplasts.

In an electron microscope though, you can get a magnification of one to 50 million, which is obviously much bigger.

And that enables you to see the inside of sub-cellular structures such as this picture here which is shown you the inside of a nucleus.

We're talking about the resolution now.

In a light microscope you can see up to a resolution of 200 nanometers.

This means you can only differentiate between larger sub-cellular structures.

So you can only see the chloroplasts and the nucleus.

You can't differentiate between smaller structures like the ribosomes.

Whereas an electron microscope, you can have a resolution of one nanometer and you can differentiate much smaller structures within that cell.

So that picture there is showing you the inside of a mitochondria.

You'd also be able to see ribosomes as well.

So the resolution of an electron microscope is much greater than a light microscope.

Now if we look at the sub-cellular structures which can be viewed within, I have touched on this a little bit, but we'll go through it again.

In the light microscope you can see larger sub-cellular structures such as the nucleus and the chloroplasts, which can be seen on those images there.

In an electron microscope, you can see smaller sub-cellular structures such as the zones and inside other sub-cellular structures.

And the condition of the specimen is a light microscope.

The specimen can be alive and needs little preparation.

Whereas in an electron microscope, the specimen has to be dead and it needs lots of preparation to stop the specimen from getting damaged.

So this is one of the limitations of the electron microscope because so far we've said that it has a much high magnification a much higher resolution, but the sample does need aloft preparation and it also has to be dead.

Let's have a quick check for understanding.

So I'm gonna ask some questions.

You are gonna give me the response.

So which microscope has a higher magnification? Electron microscope or light microscope? That is the electron microscope.

Well done if you got that.

Next one, which microscope has a higher resolution? Again, this is the electron microscope.

Number three, which microscope uses specimens that are alive? This one is the light microscope.

And finally, which microscope can view ribosomes? This one is the electron microscope.

Amazing if you've got four outta four there, really well done.

We are now going to move on to our final task of the lesson.

So your job to begin with, is to complete this table to show the features of light and electron microscopes.

Pause the video, give it your best go and then press play and I'll go through the answers.

Okay, so source of the image.

For light microscopes, it is light.

And for electron microscopes, it's an electron beam.

Magnification, is times 2000 for light microscopes, and one to 50 million for electron microscopes.

The resolution is, 200 nanometers for light, and one nanometers for electron microscope.

The sub-cellular structures, we can see larger sub-cellular structures such as nucleus and chloroplasts in light microscopes.

And we can see smaller sub-cellular structures such as ribosomes, but also inside some of those structures as well for electron microscopes.

The specimen in light has to be alive, or doesn't have to be alive, but it can be alive, and the specimen for an electron microscope has to be dead and it needs a lot of preparation as well.

Let's move on to the next part of the task.

So Sarah has a specimen she wants to view.

The specimen is dead and Sarah wants to magnify the image by 2000 and clearly see all the sub-cellular structures with a resolution of 20 nanometers.

Explain to Sarah which microscope she should use and why.

So you have to go answering that question.

Pause the video and press play when you're ready for me to go through the answers.

Okay.

As I go through this, you might have written things in a slightly different order, which is totally fine.

Just find your part of the answer when I go through it and mark it.

So to begin with, Sarah can use a light or electron microscope as her sample is dead.

A light microscope will magnify by 2000 which is what she wants, but the resolution will only go to 200 nanometers not enough to see all the sub-cellular structures.

And obviously she wants to see all the structures in the cell at 20 nanometers.

So an electron microscope will magnify by 2000 and resolve to one nanometer.

The electron microscope must be used to clearly see all the sub-cellular structures.

So in your answer, you need to come up with the conclusion that, Sarah needs to use the electron microscope to be able to get that resolution of 20 nanometers and clearly see all of the sub-cellular structures.

Absolutely amazing.

There's a lot of information that we've learned today.

If you've managed to put it all together in that answer that is really brilliant work.

Well done.

And that is the end of our lesson today on microscopes, magnification, and resolution.

I'm just gonna go through a quick summary of everything that we've learnt.

So magnification magnifies specimens, whereas resolution makes images clear to see in more detail.

Light microscopes use light and lenses to magnify samples.

Samples can be alive but they have a lower magnification and resolution, so times 2000 magnification and 200 nanometer resolution.

You cannot view sub-cellular structures such as, ribosomes with a light microscope.

Electron microscopes however, fire electron beams and specimens.

They've got a higher magnification and resolution, so one to 50 million times magnification and one nanometer resolution.

And this means that you can see smaller sub-cellular structures such as, ribosomes and also inside some of those structures as well.

That is everything that we've covered.

There's an exit quiz now for you to check whether you've learned everything that we've done, give it your best go.

I've really enjoyed going through this lesson.

I hope you have too and you've learned lots and I look forward to seeing you next time with Oak Academy.

Bye.