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Getting some Perspective
• The study of Biology involves the study of
a lot of things that can’t be seen without
the aid of a microscope.
• Activity #1:
http://learn.genetics.utah.edu/content/begi
n/cells/scale/
• Determine what you think the correct order
of the items is: Biggest (1) to Smallest (9).
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How small is a cell?
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Light microscopes
Light (or optical) microscopes use lenses to project a
magnified image of an object onto the eye.
Magnification is a measure of how many times bigger the
image is than the object:
magnification =
size of image
actual size of the object
Light microscopes are limited to a magnification of 1500×
by their resolving power (resolution). This is a measure
of their ability to distinguish between two separate points.
A light microscope cannot resolve two points that are
closer than half a wavelength of visible light (250 nm).
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Electron microscopes
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Two views of the Ebola virus
http://connect.in.com/ebola/photos-ebolavirusundermicroscope-1190603392496.html
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More about Light Microscopes
• Optical, or light, microscopes are what
you’ll be using in class to observe cells.
• Use your textbook to help you complete
the Intro to Microscopes WS.
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Preparing a specimen for microscopy
Electron microscopes
contain a vacuum, as
air particles would
interfere with the beam
of electrons.
Water boils at room
temperature in a
vacuum, so the
specimen must be dried
out completely (dead).
Optical microscopes can be used to view living specimens.
Colored dyes (stains) can be used to make specific
structures more visible under a light microscope.
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Microscope characteristics
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Proper Use of the Microscope: Important!
• ALWAYS carry a microscope with 2
hands. One under the base and one
holding the arm of the microscope.
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Proper set-up and use of the microscope
1. Orient the microscope so the stage is
facing you, not the microscope arm.
Turn/twist the eyepiece around so it is angled toward
you.
The focus knobs will be on your right.
2. Turn on the light.
3. Rotate the nosepiece to put the scanning
power objective lens in place, centered over
the hole in the stage.
The shortest lens; the lowest magnification power.
Total magnification = eyepiece lens x objective lens
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4. Place the glass slide under the stage clips,
center the specimen.
Visually place the “specimen” on the slide over the small
circle on the stage where light shines through.
5. Look through the eyepiece. Use the coarse
adjustment knob to move the stage and
bring the “specimen” into focus.
The diaphragm under the stage adjusts the amount of
light coming through.
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6. Turn the nosepiece to center the low power
objective over the slide. It must “click” into
place.
7. Use the fine focus adjustment knob to bring
the specimen into focus.
• If directed, when you go to high power, only
use the fine focus adjustment!
If the specimen goes out of focus, back up to low power
or even scanning power and start again.
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Making a “wet mount”
1-2 drops of water or
stain put over the
specimen.
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Put coverslip down at
a 45° angle and
slowly lay it down.
Wick away any
excess liquid.
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Lab 3
• Title & Purpose at the top of the page.
• Start with procedure D.
• Read directions carefully!
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