Prelab 2

Okay, folks, so welcome to your first free Lab

Week two. This is truly be the pre lab for

Monday's lab. And on Monday we're actually going

to get started with microscopy. So we're gonna.

Assign microscopes and start looking at really

neat things underneath the microscope. So this lab

three is going to be Monday's lab.

So we're going to talk about this as well in

lecture in week two. But we've kind of hinted at

this already. But it's really important to keep

the size and scale of different organisms clear in

our head. So in this particular scale you know

that humans are really, really big. This is

something that we can totally see by eye. But as

we get smaller and smaller probably as this

actually is, this shows, right? This is what we

can see with the naked eye because we get smaller

than that. So as we move to the left now, we can't

actually just see those things in front of us. The

only way we can visually see plant cells, animal

cells, and important for our class bacteria is by

using the microscope. So in our class, we're going

to use a light microscope that has a pretty good

resolution of one millimeter to 100 nanometer, but

anything smaller. So anything like a virus or

smaller, you have to use really powerful

microscopes, like an electron microscope, which

uses kind of a different technology. So that just

means that in the in our class, we'll talk a lot

about viruses, but we're not going to actually

look at a virus because it's even way too small

for the equipment that we have in the lab. But

we're going to be looking at a ton of bacteria.

And before we get to bacteria on Monday, we're

going to still be here. We're going to be looking

at, um, larger cells. So we're going to be looking

at eukaryotes.

So I'm going to post an Amoeba Sisters video that

kind of talks you through the basics of the

microscope and how to handle one. But as you watch

that video, I just want you to think about how do

we pick up a microscope? How do we place a slide

on it? How do we find that zoom in our zoom into

our organisms of interest? So those are the things

that I want you to pay attention to. And please

take notes on in terms of what's important from

that video.

Now that you're done watching the Omega Sisters

video, we're going to talk about once you found

your specimen. So once you've found the cell or

the bacterial cell that you're interested in, um,

an important thing is not just looking at it and

drawing a picture of it. That's really good and

really important. But we also, again, want to keep

in mind what is the size of the thing that we're

looking at. And so on Monday we're going to be

practicing a lot how you can actually estimate the

size. So the first important thing before you can

estimate the size of your organism is to calculate

something called total magnification. So when you

have your microscope and you have it set at a

particular objective. So remember that these these

pieces down here are objectives. And there's

different powers. There's different um strengths

in terms of how much they can make your specimen

look larger to your eyes. Right. So we have four

times the, the normal size, ten times the normal

size, 40 times the normal size and 100 times its

actual size. That's what that four x thing means.

It's how much larger you see how many times larger

you're looking at. So there's four different

objectives. Um, the microscopes that we're using.

And then there's that last piece, which is the

eyepiece. So this portion here, the thing that

you're actually putting your eyes to and looking

through to look through the microscope. And so the

eyepiece, there's only one power and it's going to

be ten x. Um, just as an aside sometimes and

eyepieces called an ocular lens. So if you want to

know the total magnification, uh, when you're

looking through that microscope, how many times

larger am I actually looking at? Then it's just a

simple equation of multiplying the two. So you're

going to multiply the power of the objective by

the power of the eyepiece. So if we have a

situation where this is set at four x the

objective is set at forex. Then the power of the

objective is four x. And you're going to multiply

that by ten x the power of the IPS. And so we get

a total magnification of 40 times 40 x 40 times.

The actual size.

Okay, I apologize folks, my recording kind of

glitched out there, but what I was trying to say

is once you have total magnification, in this case

40 x, then what you're telling people or what

you're telling yourself when you're looking

through that microscopy image, is that you are

looking at that specimen at 40 times its actual

size. That's all that 40 x means. So once you know

your total magnification, then you can go on and

calculate something called the field the diameter

of the field of view. And so all the fuel the view

is, is what you literally see with your eyes when

you look through that microscope. So when you look

through, this is what your eyes are going to see.

You're going to see a circle and then you're going

to see stuff inside of that circle. So the

diameter of that field of view is simply how long

is the line from one edge to the other edge. How

long is this red line that I drew? So to figure

out what that diameter is, that's why you need

total magnification. So I'm just going to remind

you that we have four different lenses in lab.

4010. Aw. And the biggest one is going to be 100 x.

And if we just do what we just did, the total

magnification of A4X objective lens is going to be

40 x total. Which means that if I want to know the

diameter of that red line, I'm just going to look

at this part of that table right here. And I know

that it is 4500 micron or 405,000 4500 micrometers

long. So I'm gonna let you go ahead and work

through the rest of this table. Make sure you

write this down in your notes somewhere, and make

sure you have this table handy for yourself for

the pre lab quiz when you come into lab next week.

All right. Now we are finally ready to estimate

the size of our organism so we know the diameter

of the field of view from the total magnification.

Now we're just going to figure out, okay, if we

have specimens like this, this weird purple rod

shaped organism. I want to know how long is that

organism. Right. How many micron long is that

organism? So we did this first step in the

previous slide. Now we're going to take that

diameter. And again this is a line that you're

imagining. So I'm drawing it in. But you have to

imagine it with your own, um with your own head.

And you want to imagine how many of these rods.

And I fit across that diameter. So in this case,

I'm I guess that I can fit about four and a half.

Organisms. Across that diameter. Right. So. They

figured that next step up and then were at the

last step where we use the equation. So all we're

going to do is take the diameter that we figured

out in step one, and the numbers of critters,

number of critters we figured out in step two. And

I want to make one addendum to this equation. This

is number of critters across the diameter.

Right. When you look at that field of view, it's

not that all the organisms are going to be really

nice to you and line up perfectly along the

diameter. That's not going to happen. They're

going to be scattered like in this picture. So you

have to imagine if you were to line them up side

by side, how many about do you think you could fit?

That's the kind of game we have to play. So for

this one what we're going to do is 4500 micron.

Divided by four. And I have organisms.

And so we're gonna get go ahead and think what

that's going to be.

So what you should end up with is 1000 micron per

organism. Another way of saying that is every

organism is a thousand microns long. That's that's

it. That's all you need for your calculation. So

we figured out this rod like thing is a thousand

micron long. If you wanted to, you could also

figure out the wig, the width. But in this case,

we're just figuring out the length.

So again, a couple common mistakes that people

make. Um, make sure that you count all the

organisms. Make sure that you count the organisms

that. Fit across the diameter here. And what you

don't want to do is count all of the organisms. So

sometimes what I have students do is instead of

imagining, like I taught you to, they'll figure

out how to do this. And then they're going to come

in and count one, two, three, four, five, six. And

when they set up that equation, they set it up

like this.

That's that's critters, by the way. Right. And

they divide by the wrong number. So this is going

to give you a lower estimate than what's actually

there in this particular case. Right. You're not

counting everything that you see. You have to

imagine how many feet across that diameter. The

other thing that, um, students mix up or forget

really, um, quite often, is that they mix up total

magnification and the diameter. So again, in that

equation, instead of using the diameter, what I

see quite often is they will use the total

magnification, but for some reason call that a

micron. And then. Set up their equation like this.

Right. Because we were using a total magnification

of 40 x previously. So this number is also not

going to be correct. So these are two of the most

common mistakes and size estimation that I see

from folks. So just be careful as you're um as

you're working through this. Try to remember not

to do these two things.

All right, so when you come in for lab three,

you're going to come in. You're going to grab your

microscope. I'll show you where those are.

Remember that your assigned microscope is the same

number as your cubby number. So it'll be hopefully

easy to remember. Hopefully you wrote it down in

your lab notebook and then you're going to get the

organisms. I'm going to show you how to put the

organisms on a slide, and we're going to observe

the organ organisms at 100 to 400 x total

magnification. So they're really cool. They

actually move around the bacteria later in the

quarter. Don't move around. So I think this first

lab is really nice because you could actually see

living things, which is really fun. And the

tardigrades, those are water bears are so cute.

They're so cute. I hope you see lots of them.

Okay, that's the end of this particular lab. See

you next week.

lecture in week two. But we've kind of hinted at