Hello and welcome to today's lesson from the unit: Cells.

Today you're gonna be preparing and observing a microscope slide.

There's gonna be lots of components to today's lesson 'cause it's practical, so you need your knowledge and understanding of cells and tissues, also, how to use a microscope.

And finally we're gonna be doing some observation and recording it using scientific line drawings.

My name is Mrs. Barnard and I'm gonna be taking you through to today's lesson.

And by the end of today's lesson you should be able to prepare a microscope slide with a specimen of tissue.

You should be able to observe it using a microscope and record your observations using a scientific line drawing.

So lots to get through today.

So let's get started with our key terms. So our key terms today are tissue, slide, stain, and scientific line drawing.

So just a recap, a tissue is a group of similar cells with a similar job and they work together.

And when you prepare a specimen to look down a microscope, you're generally gonna look at a number of cells together.

So you're gonna see them in the form of a tissue.

And in order to prepare specimen of tissue, you're going to have to place that onto a glass microscope slide.

So we're going to be using that word as we're preparing to make a microscope slide.

Next one, stain.

So stain is a coloured liquid that you put on top of your specimen.

It allows you to be able to see the cells and some structures inside the cells when you view it through the light microscope.

And finally, in today's lesson, our observations are going to be recorded using a scientific line drawing.

Now there's lots of different types of drawing that you'll learn about at school, but this is a very specific one that we use in science.

In today's lesson, our learning is just broken into two sections, because we're gonna have to take quite a bit of the lesson doing the practical work.

So section number one is making a microscope slide and section number two is scientific line drawing.

In today's lesson I'm gonna take you through two different types of tissue sample, one's plant cells and one's animal cells.

And we're gonna start with our plant cells and the plant that we're gonna use is onion.

Hopefully everybody recognises an onion.

This section of the onion is from the root that grows underneath the ground.

And you can see it's made up of these layers.

And these layers are tissue.

And remember tissues are made up of those living building blocks called cells.

So we need to prepare a section of this tissue.

And we can see those cells in that tissue using a light microscope.

Remember, not all microscopes look the same.

Yours might look slightly different, but all the key features of the microscope are the same.

So we prepare a microscope slide with a specimen of onion tissue and this is what a microscope slide should look like.

So the slide is a big, sorry, rectangle piece of glass.

Then you put the specimen on there, which in this case is your onion sample.

Then you put a stain on there that allows you to be able to see it, and then you put a glass cover slip over the top.

I'm gonna talk you through how to make those in the next few slides.

So there is a video here that you can watch about how to make this onion specimen.

You can pause it at points if you want to use the video, but we will talk through the method in these next few slides as well.

So this is all the equipment that you're going to need for making your plant cell slide from onion tissue.

So first of all, we've got a slide, and then we've got a little glass cover slip, and then we've got a mounted needle and some tweezers.

We've got some onion and a bit of blotting tissue and our stain, which is iodine.

So first of all, you're going to take your sample of onion, and between the layers of onion there's this tiny really thin shiny layer.

It'll come into view in a second where you can peel it off.

And that tiny thin, thin layer there that is one cell thick and you can see it's very transparent so the light can pass through it.

Now you've got the fiddly job of trying to put this on the slide and try to get it as flat as possible.

So you can use your mounted needle and your tweezers here to help you flatten it out as much as you can.

You only want it to be one cell thick just so that the light can pass through it easily, so that it can be viewed through the microscope.

Okay, so now in order to be able to see it, we're gonna have to add some stain.

And in this case we're gonna ask add iodine.

And iodine is really good at staining the different parts inside the cell.

So you put a few drops on like that.

Just be careful because iodine does stain the skin so you don't want to get on there and your clothes.

And then we're gonna get our cover slip again, bit fiddly, it's a very thin piece of glass, so please be careful, and we're going to use tweezers and the mounted needle to try to lower it gently onto our sample there and lower it down slowly.

You want to try to avoid there being air bubbles.

So you've got to lower it down slowly and then just pat it gently just to try to make sure that there's no big air bubbles underneath that cover slip there.

Okay, then if there is a little bit, you can probably blot it off around the edge, not very much on that one.

And then once it's done it should look like this.

So the method for preparing a slide of onion tissue is as follows.

Number one, you need to take a thin sample of onion tissue from between the layers with the tweezers.

Now you might have noticed this before on onions.

Onions are in layers, and in-between them there's a really, really thin layer, and it's kind of shiny, it's transparent.

So you can see through it, light can pass through it.

It's really useful because it's one cell thick.

So that's why onions are used quite a lot for making these plant tissue specimens.

The next thing you're gonna do is you're gonna place that really thin layer onto a glass slide.

You're gonna use tweezers to do that.

And then you're gonna add a few drops of iodine stain.

Remember we add the stain so that we can see the cells more clearly because it stains some of the structures in the cell.

But be careful because the stain can stain your clothes and your fingers.

So be careful when you're using it.

So the next stage is to use tweezers to place the cover slip over the specimen, you need to gently lower it down using a mounted needle.

Now the reason we lower it down slowly is so that all the air bubbles can move outwards because if you have air bubbles trapped underneath the cover slip, then they can really get in your, in the way of your view of seeing the cells.

They look like big black circles when you look at them down your microscope.

And then as you're lowering it down gently, the stain will sort of leak out the side of the cover slip slightly so you can use a little bit of tissue to gently absorb the stain.

Again, just mind your fingers, okay, try to use your tweezers in order to absorb that stain with the tissue.

And then you're going to place the slide.

That's what it should look like on the stage of the microscope.

So let's have a quick check, see if you can remember the stages of that method.

So if you can read these stages and put them into the correct order, and then pause the video and come back when you're ready.

Okay, let's get these in the right order then.

So first of all, we should have c, take a thin piece of onion tissue with tweezers.

And then the next thing that you should have is, place the specimen of the onion tissue on a slide.

And then once we've got that specimen on our slide, the next thing we need to do is we need to stain it.

So we're gonna add our iodine stain.

So B would be next.

And then finally you should have a last which is, lower the cover slip with a mounted needle.

Okay, so I said I was going to talk you through a couple of ways to make specimens of cells and the next specimen we're gonna make is a specimen of animal cells.

Now to do this, we're going to use cheek cells, so, from the inside of your cheeks.

Now you can use this video again, which talks you through it and pause it at the points, or we will go through the method in the following slides.

So this is the equipment that you'll need in order to make your animal cell slide using cheek cells.

So first of all, we have got a cotton swab to get our sample and a glass slide.

Then we've got some stain and then we've got a glass cover slip to go across the top of the specimen there, we've got a mounted needle and some tweezers.

And finally you need some disinfectant in a beaker on the side.

So first of all, what you're going to do is you're going to take a sample of cheek cells by rubbing the cotton wall bud on the inside of your cheek.

Once you've done that, you're gonna take that cotton bud and then you're going to rub it on the slide, just roll it over the slide like that.

Now, 'cause this has been inside your mouth, it's really important it goes straight into a beaker of disinfectant when you are finished.

There we go, straight in there.

Okay, so we don't pass on any germs to anybody else in the room.

Now you've got your sample on there, it's not very easy to see, so you're going to use the stain.

This is a blue stain called methylene blue and it's really good at staining animal cells.

Now we're gonna get that tiny little piece of glass cover slip, which is quite sharp, so please be careful, and we're going to gently lower it down using our mounted needle.

You can see the stain there spreading.

So we're gonna pat it down and then we're going to use some tissue to just blot that off.

We don't want to stain our fingers.

So our fingers are made of animal cells too.

So it's quite a lot of excess stain there so you can use a mounted needle to help with that.

And then that's your slide finished and it's ready to put on your microscope to view it.

So the method for preparing a slide of cheek cells is, first of all, take a cotton bud and rub it over the inside of your cheek.

And some of those cells will come off the inside of your cheek and they'll go onto that cotton bud, they'll be stuck to it.

And then you take that cotton bud and you rub it over the middle of the microscope slide.

And you might not be to see them, so it might be transparent, but you might see like a little shiny layer that's going onto the surface so roll your cotton bud backwards and forwards, and then you pop your cotton bud into some disinfectant.

'cause obviously lots of bacteria, viruses can transfer from our mouths, so we need to put it into the disinfectant.

So the next stage is we need to add stain.

Now with animal cells we use methylene blue.

Now 'cause you are made of animal cells, you'll also stain too so do be careful with the stain while you are using it.

So we're gonna add it on, and then once we've added it on, we're again gonna put a cover slip over the top.

We're gonna use tweezers 'cause remember that little glass cover slip is quite sharp and then we're gonna lower it down slowly with a mounted needle to avoid air bubbles.

And then as that stain leaks out a little bit from underneath the cover slip, the next thing we're gonna do is just use a little bit of tissue to absorb any excess from around the edges.

And then you should have your final slide now ready to put on your microscope stage.

So again, let's have a quick check.

Can you put these stages in order for making a cheek tissue specimen? Okay, let's see how we did.

So first of all, we should have rubbed the cotton bud on the inside of your cheek.

Then we're going to rub that cotton bud on the slide to transfer the cells.

Then we're gonna add some methylene blue stain.

And then finally, with tweezers, we're gonna put that cover slip there, and we're gonna lower it with a mounted needle.

So you should have b, d, c, and a.

Okay, so your practise task is to make a microscope slide and then to view it using a light microscope.

So you can prepare an onion tissue slide, a cheek cell slide, and then to look at those underneath the microscope.

Remember to have your magnification on the lowest when you start, and to adjust the focus until you can see the tissue sample, and then when you can, find focus to make it clear, and then you can increase the size of your objective lens, which will increase the magnification so that you can see those cells in details.

Okay, I hope you have fun doing this activity and I will see you after.

Okay, welcome back.

So this is what you should have seen.

The colouring might have been ever so slightly different, but your onion cells should be observed by your light microscope looking a little bit like that one on the left there with a slightly orangy-brown stain, you should be able to see the cell walls and that little structure in the middle, the nucleus.

And then with your cheek cells, they would look blue like a light blue and a dark blue in different places.

So you should have seen a sample that looks roughly like that.

So if you've got images like that, then you obviously did a great job preparing your specimens, so well done.

Okay so in the second part of our lesson we're going to be looking at scientific line drawing.

So here's an example of a scientific line drawing, and observations from light microscopes can be recorded using these scientific line drawings.

A scientific line drawing doesn't look exactly like the real image or object.

Some of you may have some really good artistic talent and you might be able to do a much better illustration of the cells that you see down the microscope.

But that's not what we're looking for in science.

What we're looking for is a clear and simple representation, which means that everybody should be able to have a go at doing it.

So the rules for producing this scientific line drawing are as follows.

You just have to select a few cells, doesn't even need to be four, two or three is enough.

And it's really important that you really focus on those to make them really big.

Okay, now if you are using the standard exercise book, it needs to take up at least half a page of your exercise book, which might seem really weird, like drawing such big pictures of something that's so small, but it's to make sure that everything inside them is really clear, that your labels are clear, and then nothing is cramped in your work.

We need to make sure that the lines are smooth and joined up.

So what that means is no sketching, okay? So not none of those little tiny lines that you do when you're sketching.

You've got to decide where your line is going to go.

You need to plant your hand down and do a nice smooth line.

You need to make sure you've got clear labels for any structures that you know, and that includes the magnification.

Now, your magnification of the image is the size of your eyepiece lens, timesed by the size of your objective lens.

You just times those two things together.

Usually the eyepiece lens is 10, so you just times 10 by whatever your objective lens is at the bottom, okay? And then there's no shading.

So we use stippling, which is these tiny little dots, rather than shading.

So everything is in the same tone of grey.

So here are some example pictures.

You can see that this is the image down the microscope.

So this is of a root tissue as you would view it through a microscope.

And you see there's loads of cells there.

So if you were to draw all of those cells it would take you forever and you wouldn't have any detail.

So you just need to select a few.

So these are some pictures as drawn in pencil rather than the one before that was drawn on the computer.

And this is a non-example, and the reason it's a non-example is because it uses sketched lines, those tiny little broken lines around the outside.

It uses shading.

There's too many cells there.

We don't need that many cells in a scientific line drawing.

And it's not labelled and there is no magnification.

So there's lots wrong with this picture, so we need to make sure that when you do yours it doesn't look like that.

So this is a good example below.

And you can see that you've got smooth, continuous lines.

They don't have to be perfect like you've drawn them on a computer, but they do have to be as smooth as possible and continuous.

Stippling has been used there to shade the nucleus and only a few cells.

And if you're choosing only a few cells, you can really take your time to make sure that you're getting the shape of those cells correct.

You can see it's labelled with root cell and nucleus, and it has the magnification written on the bottom there.

So let's just have a quick check that you understand the rules of scientific line drawing.

So I'd like you to choose two things from this list that a scientific line drawing should have.

Okay, off you go.

Okay, so the two things you should have are, smooth, continuous lines and labelling.

Okay, so those are the two that you should have.

Okay, so your practise is to be able to do a scientific line drawing of one of your microscope slides, either your cheek cell slide or onion cell slide, or both if you have time.

And you're going to select a few cells.

Remember, we're going to use continuous lines that are smooth and joined up, no shading apart from stippling.

They're gonna be a large size with clear labels and the magnification.

So, go away and enjoy that, and we will see you after to have a look at your work.

Okay, so let's have a look at your work.

So your onion cells should have this slightly square or bloggy shape and not completely.

You've got those rounded corners there and they look slightly different from each other.

You can see the lines don't have to be perfect but they do have to be continuous and smooth.

And we've got nucleus there with stippling and it's labelled onion cell and nucleus with the magnification.

And you can see with the onion cells, the cells are touching each other, whereas with your cheek cells, some of them may have been touching each other, but some of them might have been spread out just because of the method that we use.

And you can see on this cheek cell, we've got it labelled cheek cell and nucleus.

Nice smooth continuous lines.

We've got stippling of the nucleus and we've got the magnification on there.

And again, these would be nice and big, maybe taking up half a page of your books.

Okay, if you managed to get diagrams, scientific line diagrams that looked like this, then well done.

So time to summarise our lesson.

So the cells that make up tissues can be viewed using a light microscope.

A sample of tissue can be prepared on a slide to view using a microscope.

Adding a stain can make it easier to see some parts of the cell.

Changing the magnification and the focus of a light microscope enables stain cell structures to be observed.

And observations from a light microscope can be recorded in a scientific line drawing.

Well done with today's practical lesson.