Hi there, I'm Mrs. Kemp, and welcome to today's lesson all about light microscopy, observing and identifying microorganisms. This fits into the defences against pathogens, the human immune system, and the vaccination unit.

Our main outcome for today is, I can explain how microorganisms can be observed and identified using a light microscope.

These are some of the key terms that you'll use today, and rest assured that I will go through each one of these as we move through the slide deck.

But if you'd like to pause and have a little look over those yourself, please do that now.

So we've got two learning cycles for today.

The first one is the light microscope, and the second one is observing and identifying microorganisms. So of course we're going to start with the light microscope.

So microorganisms such as bacteria are far too small for us to be able to see them with the naked eye.

Okay, you wouldn't be able to just look and see them.

And therefore, we need to use a microscope in order to make those images larger so that we are able to then see those microorganisms. You can see there on the left hand side of the screen that actually we've got some bacteria there that have been observed using a light microscope.

So that's the kind of thing that we would see using a light microscope, A light microscope's got various parts to it.

Let's first of all have a look at those parts and then we'll go through, actually what each one of those parts does.

So we've got the eyepiece lens there, the objective lens, the stage, the light source, the coarse focus wheel, and the fine focus wheel.

So these are the parts that are useful on our microscope, and let's find out now how they work.

So first of all, in our eyepiece lens, eyepiece, it's obviously the part that we look through, so it's closest to our eye, and that actually has a lens in it that is usually a times by 10 magnification.

So that means it's making any image appear to be times by 10 bigger.

Then we've got our objective lenses, and usually there are three different lenses of different magnifications.

We can work out the overall magnification of our microscope by multiplying the objective lens magnification by the eyepiece lens.

So let's say that you were using a times by four on the objective lens, and that we had a times by 10 in the eyepiece, we would do 10 times four, it would give us an overall magnification of times by 40.

We've then got the coarse focus wheel, and that allows us to sort of get that image into view, and also then start to focus it.

But in order to get a really clear, crisp image, we would use our fine focus so that we can get a really nice image.

Our light source then, most light microscopes do have a lamp in them now, but some of the older kinds you might find have got a mirror on them.

Our stage is where we place our specimen, and usually you've got a couple of metal clips on the side in order to keep that slide in place.

So, onto our first check then.

Which label or labels indicate a part of the light microscope responsible for illuminating the specimen? I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, did you realise that it was B, the lamp? Excellent, well done.

Okay, which label or labels indicate a part of the light microscope responsible for magnifying the image? I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, did you realise that this one was A and also C? Both of those do have lenses in them.

Okay, method for setting up a light microscope then.

Let's go through how we actually use those parts.

First of all, we want to turn the objective lens to the lowest magnification.

Okay, so if you've got times by four, times by 10, times by 40, we would choose our times by four.

It makes it easier in order to find what we're looking for, because that view is actually much larger.

We would then place the slide on the stage, see, underneath the clips.

Okay, so we are holding it in place.

We turn on the light source.

If the microscope has a mirror, we would need to angle that so that it reflects the light up to the specimen.

But we must be careful because the lamps can get hot, and never use a mirror to reflect direct sunlight because that could also damage the back of our eyes, the retina.

So number four, looking from the side, turn the coarse wheel, so that's the larger one, to move the stage up to as close to the objective lens as you can.

You don't want to touch the objective lens 'cause you can damage the bottom of it, but you wanna look from the side and make sure that it's gone up as high as it can.

So safety, looking from the side means that you can see when to stop moving the stage upwards so that it doesn't smash into that objective lens.

Looking into the eyepiece lens, turn the coarse focus wheel to bring the specimen back into focus.

So you should be able to turn it down to take the stage downwards, because it was up as high as it would go.

Okay, and then you can make sure that you don't get any closer to that objective lens.

Then finally, we use the smaller wheel at the side, the fine focus, and that makes a much clearer image.

Okay, now we're going to watch this video to see how to safely and correctly use the light microscope.

Okay, so that was really helpful for us.

Now that we know how to use our microscope, let's go on to another check.

Put the steps in the correct order to describe how to set up a light microscope.

A, looking from the side, turn the coarse focus wheel to move the stage up so it is close to the objective lens.

B, looking into the eyepiece lens, turn the fine focus wheel to make the image clearer.

C, use the lowest power objective lens.

Place the slide on the stage and switch on the light.

D, looking into the eyepiece lens, turn the coarse focus wheel to bring your specimen into focus.

I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, number one was C.

Use the lowest power objective lens, place the slide on the stage, and switch on the light.

Two was A, looking from the side, turn the coarse focus wheel to move the stage up so it is close to the objective lens.

Number three is D.

Looking into the eyepiece lens, turn the coarse focus wheel to bring your specimen into focus.

And finally, number four, B, looking into the eyepiece lens, turn the fine focus wheel to make the image clearer.

Excellent, well done.

Okay, onto our first task of the day then, and you can get your worksheet out to record your answers.

Number one, two students are talking about how to use a microscope.

Do you agree? "Do microscopes have any risks?" "No, just wear goggles." I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, did you realise that that is incorrect? And hopefully you were sure about that, and that's because there are other risks that are involved with using microscopes.

So let's put that knowledge to the test then.

Can we write a risk assessment for using a microscope? An example has already been provided.

The example that they've given us then, the hazard, the thing that is going to cause the risk, is using a microscope with a mirror in direct sunlight and reflecting the sunlight into the eye.

What is the risk of doing that then? Direct sunlight damaging the retina at the back of the eye.

What's the precaution, so how can we make sure that we lower that risk? Do not use a microscope with a mirror in direct sunlight, and make sure the mirror is angled correctly.

I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, let's have a look at another two examples of hazards and risks.

So, the lamps on the microscope get hot.

What would be the risk? Burning the skin.

What could be a precaution? Do not touch the lamps even after switching off.

What is another hazard? Broken glass from smashed or broken microscope slides.

What would be the risk? Cutting the skin.

Precaution, store slides in boxes to protect from breakage, provide dustpans and brushes to safely clean any broken slides.

Hopefully you've got those down on your risk assessment, but if not, please do add to yours.

Okay, onto our next learning cycle then.

Observing and identifying microorganisms. When an animal or plant has been infected with a bacteria pathogen, a sample of the pathogen might be sent off to a lab for identification.

The lab may first need to grow that pathogen under controlled conditions in a growth medium.

We can see a bacterial cell there, and when they divide, they just split in two.

This will contain all of the nutrients the pathogen cells need to grow.

So a growth medium is something like agar, or it could be a broth, and it'll contain all of the things that that bacteria cell needs in order to be able to grow.

Scientists can then use a stain to help narrow down the type of bacteria that they've got in that sample.

One type of stain is called the gramme stain, and here we can see that bacteria can be either gram-positive, where they are purple using the gramme stain, or gram-negative, and they appear to be pink with the gramme stain.

Again, you do have to use a microscope in order to be able to identify this.

Once bacteria have been stained, scientists can view them with a light microscope to see what shape they are.

We've got two different shapes there on the board.

We've got the caucus, which is a sphere, so a round shape.

And then we've got the bacillus, which is a rod shape.

What can we identify about these bacteria; A-gram-negative, B-gram-positive, C-bacillus or rod, D-caucus or sphere? I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, did you realise that they are purple, therefore they are gram-positive.

And they are a rod shape, so therefore they are the bacillus.

So B and C.

Excellent, well done.

So once the scientist knows the shape of the bacterial cells, and whether they are gram-positive or gram-negative, they can use a key to help to identify them.

So on this key here, we've got either bacillus or cocci, or bacilli and cocci, and then we've got two different types of bacteria that are that cocci shape.

We've got streptococcus, where they're in a little chain, or staphylococcus, where they're kind of all clumped together.

Now, actually, when we look at that on the slide there, we can see that we've got little circles, and they appear to be in a line.

Therefore, we've definitely got the cocci, which is the sphere shape.

And because they're joined up in a little chain, we've got that streptococcus there.

Okay, scientists can grow pathogens in specific conditions.

For example, they may add one type of antibiotic to the agar.

We can see there on the picture that we've got an agar plate.

The agar is a jelly-like substance, okay? And in it, it's got all the nutrients that are needed, but we can add other things into it that only certain types of bacteria will be able to grow on.

If the pathogen can grow in the presence of an antibiotic, then it means that that antibiotic is not effective against it, it wouldn't kill the bacteria.

This can help scientists to narrow down the type of bacteria present, but it can also help doctors to know what type of antibiotic might be the most effective against that type of bacteria.

Okay, which of these features could help a scientist to identify a pathogen; A-the colour of it when stained, B-the conditions in which the pathogen grows, C-the number of pathogen cells present, or D-the shape of the pathogen? I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, did you realise the colour of it when it is stained? And also the conditions in which the pathogen grows, and the shape of the pathogen.

So A, B, and D are all correct there.

Excellent, well done.

Okay, onto our next task of the day then.

And you can record your results on your worksheet.

So, use the key to identify the type of bacteria.

So in that image there in the top corner, we've got some different type of bacteria.

Can you work out whether or not we think they are gram-negative or gram-positive? Are they bacillus or are they cocci? I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, did you realise that they are gram-positive and they're also cocci shape? They are not in a chain, and therefore we have staphylococcus.

Excellent, well done.

Onto the second part of task B then.

Staphylococcus are a type of bacteria.

One strain of staphylococcus is known as methicillin resistant staphylococcus aureus.

You may have heard of it, it stands as MRSA.

And it's considered to be what we know as a super bug, because it's really hard to kill with antibiotics.

And MRSA is resistant to the antibiotic methicillin.

How could we find out if the type of staphylococcus we have identified is MRSA? I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, so let's have a look at what we could have said.

Add the antibiotic methicillin to the agar on which the staphylococcus bacteria are grown.

Incubate, so put them in a warm environment to see if any staphylococcus bacteria grow on the agar culture.

If staphylococcus bacteria grow on the agar plate, we know it must be resistant to the methicillin antibiotic, which suggests it may be MRSA.

Okay, we're very close to finishing.

I just want to go through some of those key learning points with you.

A light microscope has two lenses and two focus wheels, which enable us to view the specimen clearly at a high magnification.

Pathogens are microorganisms that cause disease.

Scientists can use a light microscope to identify a pathogen from a sample of infected tissue based on the colour of the pathogen appears when a stain such as a gramme stain is added.

The shape of the pathogen.

Scientists can use a key to identify the pathogen isolated from the tissue sample.

Growing the pathogen in specific conditions can also help to identify it.

I've really enjoyed today's lesson, and I hope you have too.

I look forward to seeing you again soon.

Thanks, bye.