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Class
Date
Guided Inquiry • Skills Lab
Using a Compound Microscope
Lab Skills 3
Big Idea
Problem
What is the proper way to use a compound microscope and prepare a
wet-mount slide?
Each new technology allows
scientists to ask more questions
about the natural world.
Skills Objectives
Introduction
A microscope is a device that magnifies objects that are too small to be
seen by the eye alone. A compound microscope has three main parts that
work together to bring a magnified image to your eye. A light source
illuminates the object being observed. A lens on the nosepiece magnifies
the image of the object. A lens in the eyepiece further enlarges the image
and projects the image into your eye.
Thin glass plates, or slides, are used to observe biological specimens
under a microscope. The slides are made in one of two ways. A prepared
slide is made by encasing a specimen in glass. This permanent slide
can be stored and viewed many times. A wet-mount slide is made by
enclosing a drop of liquid containing the specimen between the slide and
a thin glass coverslip. This temporary slide is made to last only a short
time—usually one laboratory period.
The microscope you will use will be similar to the one shown in
Figure 1. A microscope is a precision instrument that requires careful
handling. In this lab, you will learn how to use a compound microscope.
You will also learn how to prepare a wet-mount slide.
Students will be able to
• use a microscope properly.
• prepare a wet-mount slide.
Preparation Time
10 minutes
Class Time
45 minutes
Group Size
Pairs
Advance Preparation
Check that all microscopes
were stored with the lowpower objective in position.
Students with astigmatism
who wear glasses may need to
wear the glasses while using
the microscope. Have rubber
lens protectors available for
those students to protect both
the glasses and the eyepiece
lens.
Figure 1 Parts of a microscope
Eyepiece
Body tube
Arm
Nosepiece
Stage
Fine adjustment
Diaphragm
Coarse adjustment
Base
Light source
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Skills Focus
Observe, Calculate, Compare and Contrast
Materials
• compound microscope
• microscope slide
• lens paper
• dropper pipette
• prepared slide
• coverslip
• scissors
• newspaper
• dissecting probe
Safety
To avoid damaging a microscope, follow the rules that are stated in this
lab. Handle slides gently to avoid breaking them and cutting yourself.
Alert your teacher if you break a glass object. To avoid electrical shocks,
make sure that cords, plugs, and your hands are dry when using the light
source. Use the scissors only as instructed. Do not direct the points of
the scissors toward yourself or others.
Pre-Lab Questions
1. Infer Why is it important to keep a microscope at least 10 cm from
the edge of the table?
Sample answer: If the microscope is too close to the edge of the table,
you increase the risk of knocking the microscope off the table.
2. Compare and Contrast Why are you allowed to use the coarse
adjustment when you focus the low-power objective lens but not
when you focus the high-power objective lens?
Sample answer: Because the high-power objective is longer than the
low-power objective, there is a greater risk of damaging the slide or
objective when using the coarse adjustment to move the nosepiece.
3. Predict How will the image of the letter e change when you switch
from low power to high power?
Sample answer: The image will be larger, and less of the letter will be
visible when I look through the eyepiece.
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Procedure
Part A: Practice Using the Microscope
1. Collect a microscope and bring it to your workstation.
rule 1: Always carry a microscope with both hands. Grasp the arm
of the microscope with one hand, and place your other hand under
the base. Hold the microscope in an upright position so that the
eyepiece cannot fall out. Place the microscope at least 10 cm from the
edge of your table or desk with the arm facing you.
2. The magnification for a lens is etched on the side of the objective. In
Figure 2, the lens has a 10⫻ magnification, which means that it will
produce an image that is ten times the actual size of the object being
viewed. Find the magnification for each objective lens and record
this data in the table. Then find and record the magnification for the
eyepiece. To find the total magnification under each power, multiply
the objective magnification by the eyepiece magnification. Record the
results in the table.
Step 1
Before students begin the
procedure, demonstrate how
to carry a microscope.
Figure 2 Nosepiece with objective lens
X
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Sample Data
Data Table
Objective
Objective
Magnification
Eyepiece
Magnification
Total
Magnification
Low power
4×
10×
40×
Medium power
10×
10×
100×
High power
40×
10×
400×
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Step 6
If you have any microscopes
with mirrors, show students
how to adjust the mirrors and
caution them to never use the
sun as a direct light source.
Step 8
A student’s inability to bring an
object into focus may have one
or more causes: dirt on a lens
or slide, a slide not centered
over the stage opening, an
incorrect amount of light, an
improperly aligned objective,
an objective that is raised too
high, or one that is not raised
high enough.
Date
3. Before you use a microscope, you should clean the objective lenses
and the lens in the eyepiece.
rule 2: To avoid scratching the lenses, always use lens paper to
clean the lenses. Use a new piece of lens paper for each lens because
dust picked up from one lens could scratch the next lens. Never
touch a lens with your finger. Oils on your skin can attract dust that
could scratch the lens.
4. Look at the microscope from the side. The low-power objective
should be about 3 cm from the stage. Rotate the nosepiece until you
hear the high-power objective click into position. Note that the highpower objective is longer than the low-power objective.
rule 3: Always view the microscope from the side when you move
an objective to avoid damaging the lens or a slide.
5. Rotate the nosepiece until the low-power objective clicks into
position. Find the coarse adjustment knob and practice using it to
raise and lower the nosepiece.
6. Plug in the cord attached to the light source. Look through the
eyepiece. Practice using the diaphragm to adjust the amount of light
entering the microscope.
rule 4: To avoid eyestrain, keep both eyes open while looking
through the eyepiece.
7. Center a prepared slide over the opening in the stage. Hold the slide
by its edges to avoid leaving fingerprints that could distort the image.
Use the stage clips to hold the slide in place. Make sure the lowpower objective is still in position. While you look from the side, use
the coarse adjustment to move the objective as close to the stage as
possible without touching the stage.
8. Use both eyes to look through the eyepiece. Turn the coarse
adjustment to move the low-power objective away from the stage
until the object comes into focus.
rule 5: To avoid hitting a slide, never move an objective toward the
stage while looking through the eyepiece.
9. Use the fine adjustment to bring the object into sharp focus. You
may need to adjust the diaphragm to see the object clearly. Draw
what you can see under low power in Figure 3 on the next page.
10. While you look from the side, rotate the high-power objective into
position. Look through the eyepiece and use the fine adjustment to
bring the object into focus. Draw what you can see under high power
in Figure 3.
rule 6: Never use the coarse adjustment when you are using a highpower objective.
11. Move the low-power objective back into position. Remove the slide
from the stage.
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Figure 3 Prepared slide under
low power and high power
Low Power
High Power
Part B: Prepare a Wet-Mount Slide
12. Look for the smallest lowercase letter e you can find in a newspaper.
Cut out the letter and place it on the center of a slide. Use a dropper
pipette to place one drop of water on the letter, as shown in Figure 4.
13. Place a coverslip so that one edge touches the side of the drop at a
45º angle, as shown in Figure 4. Use a dissecting probe to slowly
lower the coverslip onto the paper. This slow movement should
prevent air bubbles from being trapped between the slide and the
coverslip, which could distort the image.
Step 13
Use a projector to demonstrate
how to hold and place the
coverslip. Also show students
how to remove an air bubble
from a slide by gently tapping
the surface of the coverslip
directly over the air bubble
with a pencil eraser.
Figure 4 How to prepare a wet-mount slide
Drop of
water
Dropper
pipette
Slide
Coverslip
Probe
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14. If necessary, use a paper towel to dry the bottom of the slide. Center
the slide on the stage with the e right side up. Rotate the low-power
objective into position and bring the e into focus. Draw what you can
see under low power in Figure 5.
15. As you look through the eyepiece, move the slide to the left. Notice
the way the image of the letter moves. Now move the slide to the
right and notice the way the image moves. Move the slide toward
the arm and away from the arm and observe how the image of the
letter moves.
16. Rotate the high-power objective into position and focus the e. Draw
what you can see under high power in Figure 5.
Figure 5 Wet-mount slide under
low power and high power
e
Low Power
High Power
17. Take apart the wet mount. Discard the newspaper. Clean the slide
and coverslip with soap and water. Carefully dry the slide and
coverslip with paper towels and return them to their boxes.
18. Rotate the low-power objective into position and use the coarse
adjustment to place it as close to the stage as possible without
touching the stage. Carefully pick up the microscope and return it to
its storage area.
Analyze and Conclude
1. Apply Concepts The adjective compound means “made by the combination of
two or more parts.” In a compound microscope, which are the parts that are
being combined, and why?
Sample answer: The parts are the lenses, which are combined to produce a greater
magnification of an image.
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2. Compare and Contrast How is the image of an object seen through a high-power
objective different from the image seen through a low-power objective?
The image seen through the high-power objective will be larger and contain more
detail than the same image seen through the low-power objective.
3. Observe How did the position of the e appear to change when it was viewed
through the microscope?
The image of the letter was upside down and backward when compared with the
actual letter.
4. Draw Conclusions You observe an ant through the eyepiece of a microscope. The
ant moves toward the bottom of the slide and then it moves to the right. What do
these observations tell you about the actual movement of the ant?
Because objects viewed through a microscope appear to move in a direction exactly
opposite to that of their actual movement, the ant must have moved toward the top
of the slide and then to the left.
5. Form a Hypothesis Why must scientists cut a thin slice from a biological
specimen before they can view it under a microscope?
Sample answer: Light must be able to pass through the specimen for an image of the
object to form.
Extend Your Inquiry
Use the microscope to view a small piece of a color photograph from a magazine or
newspaper. Draw or describe the details you are able to see when the photograph is
magnified.
Students should see the colored dots that combine to form the photograph.
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