Welcome to this lesson from the unit Cells.

The title of the lesson is "Observing cells with a light microscope." So in today's lesson, we're going to be using a piece of equipment called a light microscope, and we're gonna be using it to look at structures that are too small to see with our eyes alone.

My name's Mrs. Barnard and by the end of today's lesson, you should be able to use a light microscope to observe cells.

Now, when we observe things in science, it's not just looking at them, it's using all of our senses to take in information, and to record it in a scientific manner.

Therefore, we might be able to make predictions, and explain what we can see.

So let's have a look at some of the keywords that we're gonna have in today's lesson.

The keywords we're gonna be looking at today are: cell, lens, light microscope, focus and magnification.

We will be using them through the lesson and defining them as we go, but just to make sure that we've got an agreed definition, these are the definitions that we're gonna use.

So a cell is the smallest living building block of a living organism.

A lens is a piece of curved glass, you might see them in glasses like when people wear glasses, which focuses a light in order to alter the size of an image.

A light microscope, hopefully you've seen a microscope before, but it's a piece of equipment that uses lenses to focus light and enlarge an object so that we can see it with our eyes.

We're gonna have a focus and adjusting the focus of something makes the image clearer.

And finally, increasing the magnification of an object, or an image makes it look bigger.

Okay, so those are two different words.

Focus to make it clearer and magnification to make it bigger.

So look out for those in today's lesson.

So our lesson is split into three sections today.

So section number one is that living organisms are made up of cells.

Section number two is that microscopes can be used to view these cells.

And section number three is gonna be you actually using a microscope.

So let's get into section number one, which is living organisms are made up of cells.

So all living organisms are made up of living building blocks, so sort of like Lego.

So putting Lego together to build a wall.

Except with Lego you can actually see the bricks but with living cells, you can't.

We call these living building blocks cells.

Now, you might have heard of that word before.

It's a really important word in biology.

Cells are too small for us to see.

So unlike those bricks, we can't see them.

So they are the building blocks, but we can't see them with our eyes.

We have to magnify them, we need to make them bigger to be able to see them.

So here we go, we've got a little example at the bottom here, we've got an animal.

So we've got a bird, and if we could magnify under those feathers there to the skin of the bird, we'd be able to see that that skin is actually made of these living building blocks, these cells.

And that picture there, that is what cells look like underneath a microscope.

Skin cells look like underneath a microscope.

And if we could magnify them even more, you would be able to see here, one animal cell.

So that's one skin animal cell.

So that is a living building block of an animal.

So in humans, and other animals, and plants when you get groups of similar cells together, we call them a tissue, they work together.

And in today's lesson, later on, you're going to be looking at a tissue sample, a specimen down a microscope.

And what you'll see is you'll see groups of cells together.

So when you see groups of cells together, we call it a tissue.

If you get lots of tissues together with a certain job or function, then we call it an organ.

Now, I'm sure that you know some of the organs in your body already.

Things like heart, lungs, brain, stomach, all of those things are organs.

They're made up of tissues and then, tissues are made up of these living building blocks that we call cells.

So all of our tissues, for example muscles and bones, and all of our organs, for example heart, skin, are all made up of cells, but what about a plant? We can't forget that a plant is a living organism as well.

So if we can magnify the images.

The leaves, sorry, of a plant, then this is what we would see.

You can see that these plant leaves are made up of these living cells too.

Now these look a little bit more like bricks, these ones that are in a leaf, 'cause they're quite square.

But if we magnify that even further, you can see that that's one cell there that we've picked out for you.

And you can see the wall around that one cell.

But again, we wouldn't be able to see that without a microscope.

So what is it that makes a cell living? Because we've said that it's a living building block.

It's because it carries out all of the common processes of living organisms. Now, we've gone over these in a previous lesson.

So which of these common processes that all living cells carry out, can you remember? So I want you to pause the video while you try to remember all of the common processes.

Okay so, how did you do, so did you remember that mnemonic MRS. GREN? Sometimes a good way of helping us remember all of the common processes.

So M for movement, R for respiration, S for sensitivity, G for growth, R for reproduction, E for excretion, and N for nutrition, did you get them all? Well done if you did, okay.

But that's what makes these living building blocks living, they carry out the common processes.

So time for a quick check.

So which of these statements about living organisms is true? Is it A, a living organism contains cells? B, a living organism is made up of cells? Or is it C, there are no cells in a living organism? Okay, pause the video.

All right, how did you do? The correct answer is a living organism is made up of cells.

So if you've got that correct, well done.

All right, we're going to do another check this time.

And this is called a confidence grid.

So for each of the statements, I want you to decide whether you think that they are right or wrong.

But a little bit more than that, I want you to decide how sure you are.

So are you sure it's right, or do you think it's right? Are you sure it's wrong, or do you think it's wrong? So it's gonna give you a little bit more time to get this one right, to think about it.

Okay so, pause the video and come back when you're ready.

Okay, let's see if what you thought was correct.

So animals are made up of cells.

So they are, so if you put your ticks in, "I'm sure it's right," or "I think it's right," then you are correct.

All living organisms are made up of cells.

Let's have a look, that is correct.

Now why is that different from the first one? Because the first one is that only animals are made up of cells.

So that is correct, animals are made up of up of cells.

But for the second statement, actually, all living organisms are made up of cells.

So both of those are correct statements.

The next one, cells are usually big enough for us to see without magnifying them.

That's wrong, we can't see them without using a microscope, okay? In order to magnify them, make them bigger.

And finally, cells are like Lego bricks, they're just building blocks that aren't alive.

That statement is in incorrect, it's wrong.

Now, it isn't that you can't say that they're like Lego bricks.

They are, they're like bricks that build something else.

So cells build up tissues, but they are alive.

So that makes 'em different from Lego bricks.

Okay, they are alive.

Okay, so let's have a little practise next.

So we've got some pupils here and they've drawn us some pictures of what animal cells might look like in a tissue.

What I would like you to do is to decide which one of those that you think is the best, and explain why you think it's the best.

Now, in order to explain why you think it's the best, you're also going to need to say why you think the other ones aren't the best.

So there's gonna be a few statements that you're gonna write, so choosing the best and saying why, but also a statement for each saying why you didn't choose the others.

Okay so this might take you a little bit of time to write a few sentences, so pause the video and come back when you're ready.

Okay, let's see how we did then.

So, here are the four pictures at the top that you were asked to look at.

And the best drawing was Jacob's.

Jacob's drawing is the best.

So let's see what you wrote about this.

Jacob's drawing is the best because the cells are grouped together.

So they look like building blocks.

So remember a tissue is made up of those building blocks similar to those pictures that we looked at earlier in the slides.

And also, in Jacob's picture, all of the cells are a complete unit, means the circle goes all the way around, okay? So it's a complete unit, or structure.

Why did we not choose Aisha's? So we didn't choose Aisha's because she hasn't done complete structures.

Her cells don't go all the way around, and complete themselves into a circle in her picture.

And Alex's cells are spread out.

There's like big gaps between them, okay? And in most cases, you wouldn't have big gaps between your cells that are in tissue.

And finally, why didn't we choose Laura's? Because actually with Laura's, you can actually see those cells.

You'd be able to see them with your eyes, wouldn't you? If there was a dog and it had spots on it that were that big, so they're too big 'cause they would be easier for us to see without looking down a microscope, without magnifying them.

So those are the reasons, that's the reason that Laura's is not the best picture.

So hopefully, you came up with the same or very similar conclusions in your answers, and if you did, well done.

So now, it's time for us to move on to our next cycle.

Okay, the next section of our lesson is that microscopes are used to view cells.

So further to our discussion that we've just had on cells, just a reminder that most cells are too small to see with our unaided eye, so without help.

So therefore, we can use a lens.

Now, a lens is a piece of curved glass.

You might have seen other lenses in life.

So, for example, people might put contact lenses in their eyes, or they've got lenses in their glasses.

Or you may have had the opportunity to use a magnifying glass, and a magnifying glass has got one really big lens in it.

And magnifying glasses are good for increasing the size of objects, so you can look at them closely.

However, a magnifying glass cannot make a cell big enough so that we could see it.

So we couldn't use a magnifying glass to look at cells.

What we do instead is we use a light microscope.

Now, a light microscope has got two lenses, and when those two lenses work together then we can make a cell big enough to see.

So let's have a little look at where those lenses are in a microscope.

So we've got one here that's in the eyepiece, so that's right at the top.

So that's where you're gonna look through, so that's the first lens.

And then, your second lens is the objective lens, so that's the lens that's looking directly at the object, the sample that you've got there to look at.

So when you multiply these together, these two lenses, then the magnification is big enough for you to be able to see cells.

Later in the lesson when you're using your microscope, we're going to be using a sample of cells in the form of a tissue.

So, generally, when you look at cells through a microscope, you're looking at a few cells together.

But if you get the magnification great enough, then you'll be able to see an individual cell.

So with a light microscope, we can see the single cell, and we can see some structures inside the cell, but we cannot magnify the cell enough in order to see chemicals in the form of atoms and molecules.

So this is what you can see when you look through a microscope, a light microscope at a very high magnification.

And if we compare that to a drawing of an animal cell, you can see there's quite a few structures inside the animal cell that we can't see.

We can see that big structure in the middle, which is the nucleus, but we can't see any of those smaller structures.

So it allows us to see some but not all.

And then, this is what the structure of a molecule would look like made up of chemical atoms. Now these aren't to scale, so that's not the actual size of a molecule, but we can't see anything that looks like hat inside the cell, okay? They're far too small.

So let's have a quick check.

So which of these could you only see by using a light microscope? So make your choice and then we'll discuss it.

Okay, let's see if you've got the correct answer.

So it's a cell now, you wouldn't be able to see a molecule because it's too small.

You can see a tissue without a microscope.

'cause, for example, you can see the surface of your skin.

And you wouldn't be able to see water, a water molecule would be far too small to see, but lots of water molecules together, then you would be able to see them without a microscope.

So let's see if you can explain your understanding now.

So we've got two pupils here, Andeep and Jun.

And they're discussing their aims for using a light microscope, like you are going to be doing later in the lesson.

So, Andeep says, "I'm gonna use a light microscope "to look for a water molecule inside the cell." And Jun says, "I'm gonna use the light microscope "to look at a single cell." So what I would like you to do is I'd like you to explain to Andeep or Jun whether they are actually gonna be able to achieve those aims and explain using your understanding of what microscopes can do, why they can either meet their aim, or not meet their aim.

So you're gonna have to write a few sentences.

So if you pause the video, and then we'll come back, and we'll see how you got on after.

Okay then, let's see how you did.

Just a little reminder, Andeep was gonna look for a water molecule, and Jun was going to have a look at the structure of a cell.

So we need to explain to Andeep that he will not be able to see any water molecules because they are too small.

The microscope cannot magnify them in order for us to be able to see them because the lenses cannot magnify those molecules.

Jun will be able to see the structure of a cell because the microscope lenses can magnify the cells enough to be able to see them.

But he won't be able to see all of the structures, he won't be able to see those smaller structures.

So if you've got some of those statements correct, a couple for each one, that would be great, especially good if you managed to use the word magnify and lenses in your answer because those are two of our key terms for the lesson.

Okay, are we ready to move on to the next part of our lesson? So the third part of our lesson is going to be using a microscope.

So we're gonna start with looking at a microscope and labelling the different parts.

Now not all microscopes look the same, but the key features will be the same.

So we'll start with here at the top, we've already talked about this, this is our eyepiece lens.

So this is the first section which helps to magnify the image of our specimen.

And then, we've got the objective lens.

Now, notice there are three objective lenses generally in a microscope, you can't see one, one's hidden round the back there, but you can see two.

And that little wheel that they're on, you can spin that round so that you can increase the size of your objective lens.

So there's three different sizes of objective lens.

Then you've got a stage, the stage is where you put your specimen or sample in order to view it.

I like to remember it that you put things on a stage in order to look at them in a theatre.

The other thing in a theatre that you need in order to see the actors on the stage is a light.

So right at the bottom we've got a light source there.

The difference here is that the light source is underneath rather on top of the stage.

And that's because we're looking from above.

So our light source needs to pass through our specimen that's on the stage.

And then, the light will go through the objective lens and then the eyepiece lens.

Now, you might be thinking, "Well, how can the light get through the stage?" But there is a little tiny hole in the stage.

So when you get your microscope, you'll be able to see that and the specimen has to be placed over that in order for the light to pass through.

And then, we've got two focuses on this wheel.

Now, on your microscopes you might have two wheels, but in this example you've got one big wheel round the outside and a smaller one in the middle.

So the big one round the outside is the coarse focus wheel.

So coarse means rough, so it's gonna bring your image into view, but it's not necessarily gonna be the clearest.

And then, you use your fine focusing wheel to make the image really clear.

So now, we've talked through all of those, we need to have a quick check that you can remember all of the parts.

So on the check here, we've got some missing parts.

So can you fill in the labels that are missing? So take a few minutes to do this and then, I'll come back.

Okay, let's see how you got on.

So, we've got coarse focus wheel, and then we've got a light source, and then we have got the objective lens.

So if you've got those three right, that's brilliant, well done.

So next, is how to use the microscope.

Now, you can watch this video.

This talks you through the process of using the microscope, and it's got labels on it, and you can pause it as you go, but we've also got a handy method that you can follow too.

Okay, so let's have a little look at how to use our microscope.

So if you turn it round to face you like this, you should be able to see that curved piece of glass there in the top, that's your lens, your eyepiece lens.

If we turn it sideways, it's easier for you to see all of the different parts.

Now if you look at the back, there might be a light switch, or you might have a mirror at the bottom that you need to angle, but it's really important that that light passes through that hole in the stage in order for you to be able to view your specimen.

So this is your eyepiece lens that you're gonna look through.

And these are your objective lenses, which you can change in order to change the magnification of your image.

Then, you have got your coarse focusing wheel, which gets it in roughly the right focus.

And then, the fine focusing to make a real sharp image.

You can adjust the amount of light coming through, if there's too much or too little light.

And you're gonna place your slide with your specimen underneath those clips on the stage.

So when you're ready, have a little go at making sure that that eyepiece lens is facing you.

Different microscopes, have them in slightly different ways.

And you're gonna get yourself a slide that's already prepared and you're going to put it on the stage underneath those clips.

Now, it's really important when you do this that the specimen is over that little hole where the light is coming through, so that you can visualise it.

You need to adjust your objective lens, so it's on the smallest one there.

And then, you're gonna turn your coarse focusing wheel to bring the stage as close as you can to that lens.

And then, you're gonna look through your eyepiece lens here, and you're gonna move that stage slowly away using the coarse focusing wheel until you can see a clear image.

You can sharpen up that image by just turning the fine focusing wheel there, which may be a separate wheel.

Once it's in focus, you can then increase the magnification by changing your objective lens.

And again, it should be in roughly the right place, but you can adjust your focusing wheel slightly whilst looking down the eyepiece lens to get it into view.

And finally, you may be able to use your highest magnification objective lens.

Again, slightly turning your coarse and fine focusing wheels to get it in view.

So the method for using a microscope is: turn the objective lens to the lowest magnification.

Okay so, remember I said there's those three lenses on the bottom.

So you turn it to the lowest one.

Put the slide which has your specimen on, okay, your sample on the stage underneath the clips.

Then, turn on your light source at the bottom.

Now, you may have a mirror, sometimes there's a mirror that reflects the light upwards.

Then, looking into the eyepiece at the top, turn the coarse focusing wheel, that'll bring your specimen into view.

So you'll be able to see it at that point.

And then, you're gonna turn your fine focusing wheel, and that'll make the image much clearer.

So, you should be able to see the cells in the tissue.

They might be very small on the lowest magnification.

So then, the next thing you can do is that you can turn to the objective lens up to the next highest.

And that will make your image bigger.

So it will magnify your image.

You may need to sort of adjust the fine focus again, just to be able to see it really, really clearly.

And then, you can then turn up the objective lens again to make it even bigger, again, you may have to adjust your fine focus to make the image really clear.

So let's see if you remember those, the order of that method.

So I'd like you to put these four statements in order.

So you'll need a little bit of time to read these and think about it.

So come back when you're ready.

Okay, let's see if we've got them in the right order.

So number one, you need to turn to the lowest power objective lens.

Then, you need to place the slide on the stage.

Then, you need to use the coarse focus wheel to focus on the specimen.

And then finally, you're going to use the fine focus wheel to make the image clear.

Okay, well done, if you've got those in the right order.

It's time to use your microscope now.

So your practise test today is to follow the method, and you're gonna use a light microscope to magnify and focus on cells in a tissue specimen from a plant or an animal.

Now, these will be provided for you.

And then once once you've got them on your microscope stage, we want you to focus, and magnify to the point that you can see a single cell.

Okay so, come back when you're finished and we'll have a little look at some examples.

Okay, I hope you managed to do that, and you enjoyed using a microscope.

Here are some examples of images that might be similar to the ones that you saw depending on the slides that you were given, the samples that you were given.

So this one here is a muscle tissue, and you can see the individual cells all making up the tissue there.

And then, we've got onion tissue, and then skin tissue, and then root tissue.

And in all of those examples, you can see those living building blocks, those cells that are making up that tissue.

So if you saw anything that looked like that, then well done, you managed to use a light microscope.

So now, it's time to summarise our lesson.

So today, we have learned that living organisms are made up of living building blocks called cells.

A sample of cells can be magnified using a light microscope so the individual cells appear big enough to be seen.

Cells make up tissues, and a specimen of tissue can be prepared to be viewed using a microscope.

And to use a microscope, the specimen on a slide is placed on the stage.

The microscope is turned to the lowest power objective lens.

The lens will magnify the image, this makes the cells and some structures inside them large enough to see.

Looking through the eyepiece lens, the coarse and fine focus wheels are used to focus the image, so cell structures become clear.

Okay, well done for your work today.