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Laboratory Investigation I: Microscope Lab

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • Light Microscope Parts 0:06
  • Microscope Use 6:25
    • Mount the Specimen
    • Place Slide on Stage
    • Ensure Specimen is Above Light Source
    • Lowest Objective Lens Faces Downward
    • Focus on the Image
    • Adjust the Nosepiece If Needed
    • Re-Focus
  • Human Skin Layers 10:42
  • Plants Cells 13:43
  • Human Lung Tissue 15:20
  • Euglena 18:26
  • Plant Stem 20:43
  • Mold 22:57

Transcription: Laboratory Investigation I: Microscope Lab

Hi, welcome back to, this is the laboratory investigation 1, microscope lab.0000

First, we have to discuss how the light microscope works.0007

This is technically called a compound light microscope because it involves numerous lenses where the magnification is compounded.0010

It is a compound light mic.0021

The very first microscopes would have been one or two lenses.0029

And then from there, it just got more and more magnified.0033

The microscopes in an average class now are actually quite advanced, especially compared to a few hundred years ago.0038

If we start from the top going on down, you are looking to the eyepieces.0043

The eyepieces sometimes there is one, you would close the one eye and look in with the other.0048

Sometimes there is two, oftentimes there is this inter pupil adjustment meaning, you can adjust the eyepieces.0053

Sometimes, you can actually spread them farther apart or closer together.0061

You can also rotate the little edge of the eyepiece which is minor focusing.0065

The eyepieces by themselves are times 10.0073

If you have just have the eyepieces and you are looking at something, you are magnifying that object 10 times.0077

But it is not just the eyepieces that the image is traveling through, in terms of the light reflecting off of it.0083

It is going through this objective lens, which I’m going to get to in a second.0090

The head of the microscope here, the nose piece an important part.0093

In terms of rotating these objective lenses, the way that you actually would tend 0099

to hold the microscope if you are picking it up is by the neck and the base.0104

I typically instruct students to grab the neck with one hand and put their hand under the base.0112

Just to make sure you are not going to drop it.0116

When it comes to the objective lenses, there are three, typically.0119

Some microscopes have 4, it really depends, 3 or 4.0123

The objective lenses, a lot of times there will be a red one, yellow one, and a blue one.0128

I will write on top of that in black so you can see it.0138

I have also seen ones that have like a white stripe around it, it would be a white lens.0148

The red by itself is times 4, the yellow by itself is times 10. The blue by itself is times 40.0153

You have to actually multiply the magnifications to figure out the total.0169

What I mean is, if you are looking into the eye pieces which is times 10 and 0174

you happen to have the red objective lens pointing down, it would be 10 times 4.0177

The total magnification you are looking through the red objective lens is going to be times 40.0183

If you move to the yellow one, 10 times 10 would be times 100.0190

And then finally, times 400 with the blue.0196

Like I said, sometimes there is even another one which is 100 and that would be times 1000.0202

I have heard that light microscopes, when you get to the 2000 magnification that is the limit.0210

When you go in closer and closer than that, the effectiveness of light 0215

in terms of reflecting off of an object and giving you a clear image, it starts to diminish.0219

Going beyond the light microscope capability which is beyond that 1000 or 2000 magnification, 0225

you have to use an electron microscope which is very different, in terms of how extensive they are and how they work.0230

The average classroom has got this.0237

Stage, this is where the actual specimen is mounted.0239

Usually, there are stage clips, little metal parts that keep the glass slide on the stage.0244

When you rotate some of these focus controls, the stage moves up and down, and that allows you to focus the image.0251

The stage control here moves the slide in a horizontal sense, on top of the stage, 0259

so that you can make sure that the precise part of the specimen you want to look at is right above light source.0266

Usually in the stage, in the middle, there is a hole that allows the light when it is turn on, 0271

to go up through the condenser and into the hole in the stage.0278

That is why it is light microscope, you are using light to be able to see it.0282

Since you are using light, if you want light to literally give light to what you are looking at, it has to be a very thin specimen.0285

Usually, we are talking 1 or 2 cells thick, in terms of how thin something needs to be sliced.0294

If you are looking at human tissue, let us say taking a part of a fingernail.0299

Let us say you put your fingernail and you put that down, and look at what your fingernail looks like, 0306

it might look like a dark sliver because it is too thick for light to shine through it.0310

I have students and I would not advise this.0315

I have had students that pull off a hang nail and if part is thin enough, then they can actually see through it.0319

We will look at some specimens in this particular lesson where it is a very thin, in terms of how thin a cell,0329

how thin a tissue slices, so that light can shine through it.0334

Later on in this lesson I will give instructions about how to specifically use these parts.0338

When the focus controls are being used, you start with this, this is called the coarse focus, that big one is the coarse focus.0344

This one is the fine focus.0353

You move the coarse focus first, that is when it moves the stage up and down.0357

While you are looking through the eye piece, you move the stage up and down until it becomes clear.0360

They can make it even extra crisp by moving that fine focus.0365

The condenser, I have not mentioned what it actually does.0370

You can adjust how much light is actually going through the condenser and into the stage region.0372

Those are of the major parts of the light microscope.0381

Microscope use, first you got to mount the specimen.0386

A lot of the specimens I use in my classroom are pre made.0389

There are tissues that have been in the slide and preserved in the slide for years.0393

But also, students make their own slide.0398

You take that rectangular glass slide, with a medicine dropper or pipette, 0400

you can take cells out of an aqueous environment, if you are doing a protist study.0408

Put a drop on the middle then you put a cover sit down, which is a very thin square piece.0413

That causes that drop, it just flattens the water out, it makes a nice thin aqueous environment in the cells.0422

If they are alive and moving, they will swimming around over there.0432

If it is a plant cells you have taken from a leaf, you have an environment now where they are contained flat, 0435

and in a situation where the light is going to be able to shine through.0442

You can actually see the cells and cell parts.0445

Mount the specimen, you are going to place the slide on the stage within the clips.0448

Meaning, sometimes some older microscopes actually have stage clips that you have to lift up and0452

put these metal pieces on top of the slide, like that.0460

Others have a situation where you have to brace the slide against some metal parts, like this.0465

There will be a metal region here and then a stage clip that keeps it locked in.0474

You can move this back and forth to release the slide.0482

Make sure it is placed in the clips and it is flat on the stage.0487

You also want to ensure that the specimen is above the light source.0491

One of the biggest troubleshooting things, I have a student where they spend 5 min 0494

trying to find the specimen and trying to see the cells, and they cannot find it.0500

A lot of times, the specimen is not above the light source, they are looking at another part of the slide.0503

You have to make sure that, if there is a tissue here that is right above the light source on the stage.0509

Also, make sure that the lowest objective lens, it is usually that red one, the one that is times 4, 0515

total of times 40 magnification with the eyepiece, is facing downward, there is times 4.0522

The reason why is you want to start zoomed out as far as possible.0531

Make sure that image is centered, you can see it clearly, and then zooming with the,0535

move to the yellow one, move that nose piece, so that you are looking through the times 10.0540

Refocus it, and then move to the times 40 which is a total of 400, if you want.0545

It really depends on the specimen, in terms of how far you want to go.0553

Sometimes, the times 40 which is the total for this one, with the eyepiece makes it a total of times 40.0556

Sometimes, times 100 is the best of view.0568

It depends on what structures you are trying to see.0570

I will point that out with some of the specimens we have in this lesson.0573

While looking through the eyepiece, move the coarse focus to see the image then the fine focus like I told you on the previous slide.0577

You want to start with that coarse focus, that is the one that moves the stage up and down.0581

Then, when it is nice and crisp, then move the fine.0586

When the image comes into focus, adjust the nose piece to use a higher magnification, if you wish.0589

Like I said, you can then move to the times 10, to the times 40, and refocus under that higher magnification.0593

We always go a little bit, once you have actually moved the stage to the right location, 0600

you do not have to move the coarse focus that much.0607

Just a little bit, just a fine tune, and then fine focus, you can move freely back and forth.0611

It is as if you are like looking at very tiny cross sections along the cells.0617

Sometimes, if a tissue is a little thicker than one cell, when you move the fine focus, 0623

you can start to see the top of the tissue focused then the bottom of the tissue come into focus.0629

It is fascinating how you can zoom into very specific parts of tissues by using the fine focus while you are looking through.0635

This is our first image, our first specimen.0644

A lot of microscopes, when you look through the eye piece you will see this little arrow.0649

You can actually rotate it, there is a part in the eyepiece that you can turn and this arrow will turn.0656

It is a nice a reference point, you can tell someone it is just to the right of the arrow 0662

or the arrow is pointing out what I want you to see and I’m going to take a look.0667

In terms of labeling these parts, if you were to draw what you saw in a lab notebook and label stuff.0671

If you have ever taken human anatomy or learn about the tissues of the skin, all of these on the top would be the epidermis.0680

Numerous layers of mostly dead skin cells that costly gets sloughed off.0695

These cells, every time your skin gets touched and rubbed, you have cells coming off.0701

But guess what, you are making new cells down here that replace what you are losing.0706

This section would be dermis and here is where you see melanocytes.0713

In terms of melanin producing cells that actually give you pigment.0721

You can see how they are somewhat darker.0728

Also, you can see the little nuclei right there, I’m pointing to one of them there, that is a nucleus.0731

If you are wondering why do not all the cells here have visible nuclei?0739

Why do not all of these have this nuclei?0743

These are very dried out at the epidermis, they are very dead up here.0745

In terms of visibility with staining, not as clear.0751

These are prior to this being sliced and preserved.0755

These were like completely alive, blood flows going to this area.0758

But the reason why, let us say this cell here and this cell here, the reason why 0762

you are not seeing a nucleus in every single one of them, this is a very thin cross section.0766

A very thin slice through the human skin.0773

Some of the cells that actually ended up in this image, you are taking a slice of those cells that was not right on the nucleus.0777

You might not be just to the right of it, just to the left of it.0784

Some of these cells do not have a visible nucleus and that is okay.0786

Down here, you are seeing the hypodermis also known as the subcutaneous layer where you see a lot of fat storage.0792

That is normal, even very skinny people have a lot of what is called adipose tissue down there, deep to the other skin layers.0806

Those are some of the major features of these human skin layers with this microscope view.0818

Plants cells, it is not the clearest image, it is because we are zoomed in.0824

Chances are this is times 400, in terms of the total magnification.0828

The closer you go in, the less clear it is, sometimes it even looks a little bit darker.0836

The effectiveness of the light in terms of like bringing to light a lot of these images is not the best.0841

When we explore in further, you can see some cool stuff.0848

I'm going to a draw a line around the cell wall here.0851

This is a multicellular plant tissue here, that is a cell wall.0855

Here is another cell wall.0858

If you have watched the lessons in this course, regarding organelles, like the cell lessons, 0870

or photosynthesis on plant tissues, we have got chloroplasts.0877

Chloroplast is a typical feature of plant cells.0883

Those are really the main things you see.0897

I, personally, do not see very visible nuclei.0900

It could be, it is very faint but this right here might be a nucleus.0904

This right here might be a nucleus, it is kind of hard to tell.0910

Definitely, those bright chloroplast with the chlorophyll, the green pigment molecule are very visible.0913

Human lung tissue, this is actually a patient with chronic hypersensitivity nematosis.0922

Chronic hypersensitivity nematosis is a fancy way of saying that,0949

this particular individual has had some kind of allergens, some kind of irritant end up in the lungs.0955

It causes shortness of breath, difficulty of breathing, and inflammation of the alveolar walls.0960

What you are seeing here is a lot of lung tissue.0968

You can see nuclei all over the place, all those little purple dots are the nuclei.0971

You see a lot of swelling because the typical alveolar wall, those are really thin.0978

They are one cell thick, little sacs that allow air, have oxygen fuse in your bloodstream and vice versa,0983

with CO₂ out of the blood stream into the alveolar sac, you want them to be thin.0991

But, this person, when I have got this picture off of the internet, I investigated this patient in terms of the details.0995

This particular female has no history of smoking, it is not smoking issues that has caused this.1004

It is the fact that she has, it has to do with birds, she had pet birds in the house, multiple.1010

It could be that material from the birds body, her breathing that in.1017

It could have caused irritation and swelling of these areas.1023

Areas like this, like this, should be much thinner but they have been swollen.1028

You have a lot of what are called lymphocytes.1034

You can learn more about lymphocytes, if you look at the anatomy and physiology lesson on

Lymphocytes are kind of white blood cell that has to do with responses to foreign bodies in your body.1046

Lymphocytes migrating to this area have helped to cause a lot of this inflammation.1055

Her body is dealing with this irritant or this allergen.1061

There can be medications prescribed to this.1065

Obviously, if she can do something about having the birds as pets, I know that they might have be a sentimental value to her.1067

But if they are causing her a lot of lung issues, it might be time to move on from owning birds.1077

This is human lung tissue, these spaces are the alveoli.1082

These are the alveoli sacs or alveolar spaces, literally a space in between the alveolar cells, the epithelial cells of the alveolar tissues.1088

I love doing a protist lab with my biology students, where we look at euglena amoeba perimysium.1108

Euglena is one of those really cool plantlike protists.1116

What you cannot see, sometimes it is very hard to see it under microscope and you are zoomed in, 1121

is there is this from region here that actually has a flagellum.1126

I’m going to label it as if it is there, oftentimes, it is really hard to see their little tail.1133

What you can definitely see is, this is called a stigma which has what is nicknamed an eyespot.1141

Photosensitivity is one of the cool characteristics of these euglena cells.1155

They are single celled beings, eukaryotic related to you or I, more or so than related to bacteria.1160

It is a very distant relationship.1166

The eye spot is the most primitive way of viewing something, in terms of vision.1170

They can see light, the lack of light, the abundance of light, and that is it.1177

This allows them to notice where light is so they can swim towards it.1181

It is a great adaptation because they are doing photosynthesis.1185

You can see chloroplasts all over the place in the cell.1189

The nucleus is most likely here, it is really difficult to tell, this is a fuzzy view.1196

You definitely can see the chloroplasts all over the place, it is great.1207

If you look long enough on a microscope slide, if you look carefully enough at this end, 1213

you can sometimes can see the flagellum whipping about.1221

It looks kind of transparent, it is not colored green, you have to look carefully.1225

They can morph in all these different shapes.1231

I have seen some that look perfectly round, I have seen some doing spirals, 1234

getting thinner, getting longer, they are very flexible.1239

A plant stem, this is actually from a kind of flowering plant nicknamed a monocot.1244

When you actually do the cross section, one cell thick, one cell thin, through a monocot’s stem.1253

This is typically what you are going to see.1259

These cells in here that just look blank, this is nicknamed ground tissue.1262

The tissue that is surrounding the cells that are actually doing something physically, in terms of physiology.1271

The ground tissue is important because without the ground tissue stacked upon itself, you would not have the stem growing up.1279

You would not have that support.1286

The ground tissue is in here, also it is sometimes nicknamed pith.1288

The tissue that is really doing more of a role, in terms of this part of the stem is the vascular bundles.1294

I will label this in green, what you are seeing here scattered throughout, all these little guys,1303

if you would zoom in, it may look like little monkey faces.1309

These are vascular bundles or vascular tissue.1313

Here we got xylem transporting water and phloem transporting mainly sugars.1326

They are scattered all throughout.1336

If you are looking at a dicot or eudicot stem, you would see the vascular bundles in a ring1337

around the outside with very dense pith from the inside.1344

You could see that scattered throughout the stem.1347

You have these little monocot faces they look like.1350

Through part of it, you get transportation of water through another part that you get transport of the sugary substance.1354

The last part, I will label in blue, is the dermal tissue.1361

You can call it the epidermis, analogous to our skin.1366

It is the outer layers, protective for the stem.1370

Here we got mold, interestingly enough, it looks almost see through.1379

That is really fascinating what we are looking at here, this is extensive hyphae.1387

This right here, just one strand, you can call hypha.1394

A bunch of it you can call hyphae.1400

There are what appeared to be some spore producing structures scattered throughout.1407

Spore containing structure also known as, with mold you can call it a zygosporangium.1422

It would be an appropriate name.1439

The hyphae is the extensive network of filaments, cells that are all together, 1440

that allow the mold to penetrate into whatever it is feeding off of.1447

Also, to allow it to have some kind of bodily structure for its reproductive structures, the spore bearing structures, 1451

to come up out of their food source, and release spores and spread throughout.1459

Specifically, the part of the hyphae that is embedded in the food source will be called mycelium.1466

Since, we do not know what specific part of the mold we are looking at, 1473

this might be mycelium with some spores, combined in this particular view, it is hard to tell.1476

Definitely, all of this is hyphae, extensive hyphae from mold.1484

Thank you for watching