Lab 1: Using the Microscope
Biology 2201, Unit 1
Safety in the Lab
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Read and heed the Laboratory
Safety guidelines on pages x to xi in
the McGraw-Hill Ryerson Biology
text.
Read the 1st Lab on pages 15 to 19
and page 24 in the text.
Familiarize yourself with the
locations of the safety equipment in
the Science Lab.
Magnification
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To calculate the total magnification of an
object, multiply the power of the eyepiece
by the power of the objective.
For example, if the eyepiece magnification
is 10x and the low-power objective is 4x,
the total magnification of the low-power
objective is 10 x 4 = 40x.
Illumination
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The light source (electric bulb) directs light
through the diaphragm, the specimen and
the lens.
Look through the eyepiece, and adjust
the diaphragm until the view is as bright
as possible.
Field of view
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The area that you can see through the
eyepiece is called the field of view.
To determine the field of view, place a clear
plastic ruler on the stage.
With the low-power objective in place, use
the coarse adjustment knob to focus on the
ruler. Position the ruler so that one of the
millimetre markings is at the left edge of the
field of view.
Calculate the size of your F.O.V.
The diameter of the field of view under low-power,
shown here, is about 1.5 mm.
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If you know the diameter of the field of
view for the low-power lens, you can
calculate the field of view for the
medium-power lens as follows
(example only):
Med-power FOV =
Low-power FOV x Magnification of low-power objective
Magnification of med-power objective
= 2 mm
x 4X
10X
= 2 mm
x 0.4
= 0.8 mm or 800 µm is the Med-power FOV
Formula for calculating the
high-power FOV
High-power FOV =
Low-power FOV x Magnification of low-power objective
Magnification of high-power objective
Measurement
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Objects in the field of view of a
microscope are usually measured in
micrometres (µm).
For example:
1 µm equals 0.001 mm
1000 µm equals 1 mm
From our example, the FOV under the
medium-power objective is 0.8 mm x
1000 = 800 µm.
Calculating specimen size
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You can determine the size of a specimen,
such as a microscopic amoeba, by
estimating how many could fit end to end
across the field of view.
To do this, divide the field of view by the
number of specimens.
For example,
if the field of
view in the
illustration is
1500 µm, what
is the diameter
of each
amoeba?
Answer:
Specimen size = FOV divided by # of specimen
= 1500 µm divided by 5
= 300 µm is the diameter of an amoeba.
Focusing techniques
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The low-power objective should be in position.
Center the specimen over the opening in the stage.
Look through the eyepiece. Slowly turn the coarse
adjustment knob until the object is in focus.
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Carefully rotate the revolving nosepiece to the
medium-power objective.
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Use the fine adjustment knob to sharpen the focus.
Watch the side of the stage as you rotate the nosepiece to make
sure that the objective lens does not strike the surface of the slide.
Adjust the focus using only the fine adjustment knob.
To finish, carefully rotate the nosepiece until the lowpower objective is in place; remove slide; power off.
Biological drawings
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Biological drawings are drawings of
biological specimens that you observe
under the microscope.
A scale drawing is a drawing in which
the proportions of what you observe
through a microscope are kept
constant.
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Label your drawing.
Indicate the total magnification.
Calculate the actual size of the specimen.
Depth of field
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The depth of field is the vertical distance
(the “thickness” of an object) that remains in
focus at any one time while the specimen is
being viewed.
Video link
Preparing a wet mount
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Start with a clean slide and coverslip.
Hold the slide and coverslip by their edges to avoid
getting your fingerprints on their surfaces.
Using tweezers, position the specimen in the
centre of the slide.
With the medicine dropper, place one drop of
water on the specimen.
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Hold a coverslip over the sample at a 45° angle.
One edge of the coverslip should touch the
surface of the slide near the specimen.
Lower the opposite edge of the coverslip over the
sample. Make sure that no bubbles form beneath
the coverslip.
Next day we meet in the Lab.
Be prepared!