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“Pinky, what is on the kitchen table?” “Oh, it’s my protists.
I’m hoping tofind some euglena, maybe some paramecia.
I took this sample from—”“Stop, I mean, WHY is it on the KITCHEN table?!” “Oh, I got distracted.
I was going to take some drops and put iton a slide while I set up my microscope.
” “Yes, well, please get your green wateraway from where we eat.
” “Green water? Don’t be ridiculous, Petunia, there are tons of protists in here.
We just have to find them.
” “Well, I think you’re out of luck.
” “The protists that I’m looking for areunicellular, meaning, they’re made up of one cell.
And generally, you need a microscopeto see them.
Never used one of those.
” “You’ve…never used a microscope before?” “No.
” “Well you know what that means?” “I’m afraid about what that means.
” “We must explore the world of…microscopes!” First of all, let’s focus on a few termsthat are important in order to understand microscopes.
Magnification is one.
That’s really what most people think ofwhen they think of a microscope.
And we’re going to talk more about thatin a moment.
But another term that is important is resolution—basically, are you able to distinguish between two objects? This is important as otherwise two objectscould actually look like one object, because you can’t distinguish between them.
So, for example, if a microscope had a resolutionof 0.
2 microns, that means two objects needs to be 0.
2 microns or more apart in order tosee that they are two different objects and not one.
If you want to understand the physicsof how resolution works and how it’s calculated, we have a great further reading suggestionin the video details.
So let’s talk about some different typesof microscopes that all take into account this need for magnification and resolutionin order to see specimens.
First, light microscopes.
If you’re in a classroom, this is likelywhat you have.
And, as its name would suggest, it uses light in order to see an image.
Brightfield light microscopes tend to be whatpeople are familiar with- typically producing a darkerimage on a light background.
With a darkfieldlight microscope, you have a piece that blocks the light source, called a light stop.
Theidea is that most light has been blocked so the only light you see is light reflectedor refracted from structures within the specimen that you’re looking at.
So, you tend tosee light images on a dark background.
There are many other types of light microscopestoo.
We have a great link for further readingsuggestions to learn how each of these work, and some of these are fascinating—some relyon interference, some rely on using a laser…but the thing to keep in mind is, there are certaintimes when one of these types of light microscopes is more ideal than another.
For example, aphase-contrast microscope can give you a very detailed image of a living specimen withoutrequiring any stain, and the detail it provides can be far better than the typical brightfieldmicroscope.
So light microscopes use light in some formto see a specimen.
But not all microscopesare light microscopes.
For example, what if we wanted to see a virus? Viruses are generallyvery small- typically much smaller than the average bacterium.
How can we increase magnificationand resolution abilities to see them? That’s where electron microscopes come in.
Electronmicroscopes use electron beams to visualize images.
Transmission Electron Microscopes(TEMs) tend to be most ideal for visualizing structures within a specimen while ScanningElectron Microscopes (SEMs) tend to be most ideal for visualizing the 3D surface.
Let’s come back to the typical microscopeyou might see in a classroom, which happens to be the one that I own.
A brightfield light microscope.
Here is our light source.
Light passes through this, the condenser lensto focus the light on the specimen.
The level of light can be adjusted by this, the diaphragm.
Our specimen—likelyto be on a microscope slide—will be placed on the stage here.
Light will be reflected, refracted, or absorbed by the specimen.
But we rely on these lenses here—the objectivelens and the eyepiece lens—to get our total magnification.
In fact, this is often referredto as a compound microscope, because it has two sets of lenses.
You can see that the objectivelenses are attached to this revolving nose piece which allows them to be rotated so youcan select a certain one that you want to use.
With my particular microscope, I havethree objective lenses.
A scanning objective lens that magnifies 4times, the low power objective lens that magnifies 10 times, andthe high power objective lens which magnifies 40 times.
But don’t forget the eyepiece lens becausethat also magnifies images, and my particular eyepiece lens magnifies 10 times.
So let’s say I use the scanning objectivelens.
I would multiple that objective lens magnificationlevel by the eyepiece lens magnification level so that my total magnification is 40times.
Now, you’ll also notice there’s a lotof knobs here.
Let me introduce you to theknobs.
This large knob here is known as the coarsefocus and then this smaller knob here is known as the fine focus.
Both of these knobs raise or lower the stage, which helps with focusing.
The coarse focus knob will move it more dramaticallywhereas the fine focus knob will move it in smaller increments.
These knobs- the stage knobs- don’t movethe stage up and down but rather from side to side instead.
It helps you explore what’son the slide itself, but it isn’t adjusting the focus of it.
Not all microscopes havethose stage knobs; sometimes you have to move the slide manually.
This is the microscope arm and the base.
Whenever you pick it up, you want to makesure you have one hand underneath supporting the baseand the other hand holding the microscope arm.
Since it plugs in, you want to make sure thereisn’t water around it.
So, let’s take a look at what’s in thiswater sample here.
I’m going to do somethingcalled a wet mount to prepare my microscope slide.
I’m going to drop a drop or two ofmy water sample onto the slide using a disposable pipette.
It’s like a very fancy eyedropper.
I’m going to put a cover slip on top.
There’s some techniques to doing awet mount to avoid air bubbles that you can check out online.
Air bubbles actually canlook kind of beautiful under the microscope—which can lead to great disappointment when youfind out they’re not some amazing microscopic organism but rather just an air bubble—something I may or may not know by experience.
I’m going to put the slide on the stage.
I’m going to use the stage clips here tosecure the slide.
Light is on, and I already have the scanningobjective lens here ready to go, which is good, because I want to findthe specimen first.
I can adjust the lightlevel if I want—but just know that super bright doesn’t always mean the best image.
I can look through the eyepiece and use thecoarse focus knob to move the stage up or down slightly to focus.
Euglena! I can also fine-tune focus it with the finefocus knob.
I can use the stage knobs to center my image.
Now that I found it with the scanningobjective lens, I’m now going to move up to the next magnification level.
So, remember, total magnification would be 100 times.
Since I had already focused it with the scanningobjective lens, it’s likely I only need to use the fine focus knob to adjust the focusat this level.
I could continue to move up to the high powerobjective lens, which would give me a total of magnification of 400 times.
Now 3 additional tips about using microscopesthat I just want to mention.
1) Most microscope slides are glass so theycan break if dropped.
And if using cover slips, keep in mind they are extremely easy to lose if not careful.
2) Always be aware of where the slide is whenyou’re moving the stage up and down with the focus knobs.
It’s possible to move the stage too closeto the objective lens and actually crush the slide.
3) If it’s hard to see your image even whenfocusing, you may need to clean the lens.
But you need to do this by wiping it withlens paper.
Not regular tissue.
When you’re done with the microscope, makesure the slide is removed, turn off the light, lower the stage to its lowest position, andreturn the lowest power objective lens over the stage.
Unplug it and wrap up the power cord.
And if you have a cover, cover the microscopebefore putting it away.
Keep in mind there are some techniques tobetter visualize some specimens such as using different stains or using immersion oil athigh magnification to increase resolution.
Definitely something to explore that thisvideo doesn’t go into.
Microscopes open up an entire world that youcan’t see with the naked eye.
Microscopescan also complement what you might be learning in life science.
Studying mitosis? Check outthe cross section of an onion root tip, where lots of mitosis happens.
Studying plant responses? Take a look at stomata from a thin sampleunderneath a leaf.
Studying osmosis? Takea look at how aquatic plant cells respond to different salt concentrations.
Endlesspossibilities to explore endless curiosity.
Well that’s it for the Amoeba Sisters, and we remind you to stay curious.