This lesson is called "Observing Root Hair Cells Using a Light Microscope, Practical" and is from the Unit, "Transport and Exchange Surfaces in Plants".

Hi there, my name's Mrs. McCready and I'm here to guide you through today's lesson.

So thank you very much for joining me today.

In our lesson today, we're going to use a light microscope to observe a plant root hair cell and have a go at producing a scientific drawing of it.

So are you ready for a practical lesson today? I hope so.

Now, in our lesson today, we're gonna come across a number of key words and they're listed up here on the screen for you now.

You may wish to pause the video to make a note of them, but I will introduce them to you as we come across them.

So in our lesson today, we're going to first of all remind ourselves of the light microscope before we observe root hair cells using it.

So are you ready to go? I certainly am, let's get started.

So cells are usually too small to see with the unaided eye and therefore we can use a light microscope to see them instead.

Now a light microscope has various parts to it.

It has an eyepiece lens through which we are looking.

It has objective lenses, which can change the magnification of the object that we are viewing.

It has a stage onto which we place our specimen.

It has a light source, either a lamp or a mirror to reflect an external lamp, and it has a course focusing wheel and a fine focusing wheel.

Now all of these parts of the microscope have different roles.

The eyepiece lens has a magnification usually of about 10 times.

The objective lenses have three magnification lenses, usually times four, times 10, and times 40, but that may well differ for the microscope that you were using.

The course focusing wheel provides large adjustments in the focus and the fine focusing wheel provides minor adjustments in the focus.

The light source illuminates the subject that we are observing and allows us to be able to actually view it, and the stage is where the specimen is placed.

So which label or labels indicate a part of the light microscope which is used to bring the image into focus? I'll give you five seconds to think about it.

So you should have chosen that D, the course and fine focusing wheels are the part of the microscope used to focus an image.

Well done, now to set up a light microscope, you must first of all turn the objective lens, that's B in the diagram to the lowest magnification, and then place the slide onto the stage C and fasten it with the clips.

Then you need to turn on the light source D and make sure that the light is being reflected through the specimen.

Now, if your microscope does not have an inbuilt lamp, you need to make sure that you are using a lamp, an external lamp to reflect off the mirror, never direct sunlight.

And you also need to remember that lamps get hot.

So be careful when you are handling them, either the external one or the one on the microscope itself.

Then to view the specimen, you need to firstly make sure that the course focusing wheel is used to bring the objective lens and the stage as close together as possible.

If you look at the side of the microscope in order to do this, this means that you can stop before crashing and ramming the stage into the objective lens, damaging potentially the objective lens or the specimen itself.

Then once you've done that, you can then focus the specimen by looking down the eye piece and using the course focusing wheel, moving the course focusing wheel so that it moves the stage away from the lens and brings the specimen into focus.

If you need any further fine focusing, then use the fine focusing wheel in order to do that to make the picture as sharp and as clear as possible.

So watch the video to see how to safely and correctly set up a light microscope.

Okay, let's check our understanding.

What I'd like you to do is to put these steps into the correct order to describe how to set up a light microscope.

A says, looking from the side, turn the coarse focus wheel to move the stage up so it is close to the objective lens B says, looking into the eyepiece lens, turn the fine focus wheel to make the images sharp and clear as possible.

C says, use the lowest power objective lens.

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

And D says, looking into the eyepiece lens, turn the coarse focus wheel to move the stage away from the lens.

But what is the correct order of those steps? I'll give you five seconds to think about it.

Okay, so you should have firstly chosen part C, then part A, then part D, and finally part B.

Did you get them in the right order? Well done if you did.

So what I'd like you to do now is to firstly write down the names of the parts A to E of the light microscope.

Then I would like you to explain why it is important to look from the side when using the coarse focus wheel to move the stage upwards towards the objective lens.

Then finally, suggest why the mirror must not be used to reflect direct sunlight if the light microscope has a mirror at all.

So pause the video and come back to me when you are ready.

Okay, let's quickly check our work then.

So firstly, I asked you to write down the parts A to E.

A is the eyepiece lens.

B is the objective lens, C is the stage, D is the light, E is the coarse focus wheel and F is the fine focus wheel.

Well done if you've got all of those correct.

Then I asked you to explain why it's important to look from the side when bringing the stage and the objective lens together.

And you should have said that by looking from the side, this means you can see when to stop moving the stage upwards so that it doesn't smash into the objective lens, and that could cause damage to either the lens or the specimen.

Then I asked you to suggest why if your light microscope has a mirror, you should not use direct sunlight to reflect up through the light microscope.

And you should have said that this is because you should never use a mirror to reflect direct sunlight because the light is too bright and could damage the light sensitive cells in the retina of the eye.

This is true not just for using microscope, but for any time.

Well done if you've got all of those correct.

Okay, let's move on to observing the root hair cells.

So if we magnify the roots of a plant, we will see that the outermost part of the root has specialised cells called root hair cells, and these are highly adapted to enable them to absorb water and mineral ions from the soil efficiently.

Now, if we look at them without a light microscope, we can see that they look fuzzy and that's because of the root hair cells.

But what we're gonna do is observe those using a light microscope to see them in much more detail.

So root hair cells have a large protrusion, sticky out bit from the surface of the cell, and this is called the hair.

Now, it's not actually made of hair.

It's actually an extension of the cytoplasm in the cell membrane.

And this greatly increases the surface area of the cell, which means that the plant will be able to maximise the amount of water and mineral ions it can absorb into the plant because there is a fantastically large surface area over which these processes can absorb the mineral ions and water into the cell.

Now we can observe the root hair cells using light microscope.

This is what they are likely to look like when you observe them down the microscope.

So we can see that the large part on the left hand side are the root cells, the cells that combine up to make the actual root itself and the sticky out bit is the root hair cell itself.

So you can see it's a long protruding stick, bit like a hair, and that is what you are going to have a look at today.

So let's quickly check our understanding, which of these statements are true? A, root hair cells are too small to be seen with a light microscope.

B, root hair cells have a protrusion from the cell surface.

C.

root hair cells are found on the outermost part of the root and D.

root hair cells are made of hair.

I'll give you five seconds to decide.

Okay, so you should have said that B and C are both true.

Well done.

Now, in addition to observing the root hair cell, I would like you to try and have a go at drawing a scientific line drawing.

Now, in order to do this successfully, there are certain principles in drawing that you need to follow.

Firstly, there must be no feathery lines or sketching.

This is not a work of art, this is a scientific drawing.

There must also be no shading.

So don't be tempted to shade in the nucleus or the vacuole or any other part that you can see.

There must also be no arrow heads on the label lines that you draw.

And when you are drawing your label lines, you need to draw them with a ruler.

So these are the principles of good scientific drawing, no feathery lines or sketching, no shading and no arrow heads.

And this is what you're going to be completing today.

So which of the following rules apply to scientific drawings? A, lines drawn with arrowhead, B, no shading, C, feathered lines and D, labels added.

I'll give you five seconds to think about it.

Okay, so you should have said that there should be no arrow heads on the lines drawn, that there also should be no shading, that the lines must not be feathered, but labels must be added.

Well done if you got all of those correct because you'll need to remember to do that.

Now, when we are making a scientific drawing, it's also good practise to add the magnification on and this is because what it does is give an indication of scale to the drawing.

So it's possible to get an idea of how small or big the thing was that you were looking at when you drew it.

Now, in order to calculate the total magnification, you need to multiply the magnification of the eyepiece lens, which is usually times 10 by the magnification of the objective lens that you used when you did the drawing.

So you need to make sure that you take a note of that and can therefore write the total magnification down on your diagram accordingly.

So if a specimen was observed using an eyepiece lens for the times 10 magnification and an objective lens for a times 10 magnification, the total magnification will be eyepiece times objective lens, which is 10 times 10, which is 100, a total magnification of 100.

Okay, your turn then.

So a specimen is observed using an eyepiece lens with a magnification of times 10 and an objective lens with a magnification of times 40.

So what is the total magnification? I'll give you five seconds to work it out.

Okay, so you should have said that the total magnification is the eyepiece lens times the objective lens.

That's times 10, times 40, and therefore that's a total magnification of times 400.

Well done if you got that correct.

So your finished line drawing should look similar to this, where you can see both a few of the main cells within the root plus the root hair cell, properly labelled using a ruler and no arrowhead with nice crisp clean lines, no shading and no feathering, plus the total magnification added to give an idea of scale.

So that is what you are aiming for in our lesson today.

Let's quickly check our understanding, which of these is the best scientific line drawing? I'll give you five seconds to think about it.

Okay, so you should have said that B is the best scientific drawing because it has no shading, it has no feathering, and it has no arrow heads.

Well done, so what I would like you to do now is to set up your light microscope and use it to observe a root hair cell on a slide.

Then using that image, produce a labelled scientific drawing of a root hair cell based on your observations and the rules for scientific drawing are shown there on the screen.

Remember also to calculate the total magnification and add this to your drawing.

Now this is a challenging task, especially if you have never done this before.

So take your time and be as accurate as you can and pause the video.

Come back to me when you are ready.

Okay, so how did you get on with that? As I said, it is really quite a challenging task to complete, especially if you've never drawn whilst looking down a light microscope before.

But your diagram, your drawing should be similar to this.

So you have not feathered any of the lines.

There is no shading.

The label lines are drawn with a ruler with no arrow heads, and you've added the magnification to your diagram as well.

Well done if you've even got part of that drawn, because that really is very difficult to do indeed.

Okay, we've come to the end of our lesson today, and we have seen that a like microscope has two lenses and two focusing wheels, which enables us to see specimens nice and clearly, and also at a high magnification.

Now, root hair cells of a plant can be observed using the light microscope and their shape is visible and can be recorded using a scientific line drawing.

Now, scientific line drawings require no feathering or shading, no label lines with arrows, and those label lines must be drawn with a ruler and the total magnification added to the image, and that we can calculate the total magnification by multiplying the magnification of the eyepiece lens by the magnification of the objective lens that we used to observe our specimen with.

So I hope you've enjoyed your practical lesson today.

Well done again, and thank you very much.

I hope to see you again soon, bye.