Download Lab #1

Biology
Microscope Lab #1
Parts, Functions and Using the Microscope
Name __________________________
Period __________
The microscope is possibly the most important and valuable instrument used by biologists. The
simple microscope used by Anton van Leeuwenhoek in the seventeenth century consisted of only
one lens. Later, other scientists discovered that by putting two lenses together, the magnification
could be multiplied many times. The modern compound light microscope has two lenses and
achieves high magnifications. It can magnify objects up to approximately 400 times their natural
size and allows scientists to investigate worlds that are otherwise too small to be seen.
An opportunity to learn about and use this valuable instrument is now yours. The microscope is
simple to use, but it is delicate and must be handled carefully. In this investigation, you will
learn about the parts of the microscope, what their functions are and how to use the microscope
properly.
Purpose:
In this investigation you will:
a) know the names and functions of the parts of a microscope
b) use a microscope in such a way that it will remain clean and in good working order
c) know the amount of magnification for an image based on the power of the ocular lens
and objective lens
d) use the proper steps in focusing with the low power and high power objectives
e) learn how to prepare a wet mount
f) compare an object viewed with a microscope to that object viewed by the unaided eye
NOTE: Carry the microscope in an upright position,
with two hands (one on the arm, one on the base) close to the body.
Procedure:
Part A. Learning the Names and Functions of Parts of a Microscope
Use the diagram on the first page to answer the following questions.
1. A mirror is attached to some microscopes by means of a swivel joint. Position the curved
surface of the mirror so that it is turned toward a light source such as ceiling lights, windows
in the room, or a desk lamp. (CAUTION: Never use direct sunlight as a light source. Direct
sunlight will damage your eyes.) A lamp may be built into your microscope (which replaces
the mirror and outside light source). If your microscope has a lamp, be sure to turn it off
before unplugging. Does your microscope have a lamp or mirror?
2. A diaphragm controls the amount of light entering the microscope. Turning the diaphragm
adjusts the amount of light passing through the microscope. An iris diaphragm works similarly
to the shutter on a camera and the iris of your eye. Moving a lever causes the opening to
increase or decrease in size, allowing for more or less light to pass up through the stage opening.
A disc diaphragm is a wheel that has openings of various sizes that can be rotated into position.
The larger the opening that is in position, the more light gets through. What type of diaphragm
does your microscope have?
3. The ocular lens is the lens nearest your eye. It usually has a magnification of 10X.
What is the magnification of the ocular lens on your microscope?
4. The revolving nosepiece has objectives that each have a lens of varying power (ability to
magnify). There are usually two or three objectives. The objective that magnifies the least is
the “low power objective”. The objective that magnifies the most is the “high power objective”.
a) How many objectives are on your microscope?
b) What is the magnification of the low power objective on your microscope?
c) What is the magnification of the high power objective on your microscope?
d) If you have a third objective, what is its magnification?
5. The total magnification of the object being viewed can be calculated by multiplying the
power of the ocular lens by the power of the objective on the revolving nosepiece.
a) Using your microscope, what is the total magnification of an object being viewed using
the low power objective?
b) What is the total magnification using the high power objective?
c) If you have a third objective, what is the total magnification using the mid power objective?
6. Place a check mark in the square next to each part of the microscope you can locate.
Use the diagram on page one for help.
⎕ diaphragm
⎕ high power objective
⎕ lamp or mirror
⎕ low power objective
⎕ revolving nosepiece
Do not continue with the lab until you know where these five parts are located.
7. Place a check mark in the square next to each part of the microscope you can locate.
Use the diagram on page one for help.
⎕ eyepiece
⎕ stage
⎕ coarse wheel adjustment
⎕ stage opening
⎕ fine wheel adjustment
Do not continue with the lab until you know where these five parts are located.
Part B. Using the Microscope
1. Turn on the lamp or position the mirror toward the light source.
2. Turn and click the low power objective so that it is directly over the stage opening.
An objective is in proper viewing position when directly over the stage opening.
Most microscopes will “click” when the objective is in proper viewing position.
3. Look through the eyepiece of the microscope. The circular area you see is your
field of view. Keep both eyes open. Keeping both eyes open will reduce eyestrain.
(Covering one eye with your hand may help).
4. Adjust the mirror and diaphragm to make the circle of light as bright as possible.
5. Look to the side of the microscope. Slowly turn the coarse wheel adjustment back
and forth. DO NOT force the wheel once it stops. When the wheel stops, turn it
in the opposite direction. Note the movement of the low power objective in relation
to the stage. (On new microscopes the stage may move rather than the objectives.)
a. In which direction does the objective move as you turn the coarse wheel
adjustment toward you?
b. In which direction does the objective move as you turn the coarse wheel
adjustment away from you?
c. Why should you always watch from the side to start with the objective close to
the slide, and then as you are looking through the ocular lens only move the
objective away form the slide?
Total magnification of an object is calculated by multiplying the magnification of the
objective by that of the eyepiece. The eyepiece usually contains a lens that magnifies 10
times (10X). Often times the low power objective also contains a lens that magnifies 10
times (10X). For these lenses, the total magnification would be calculated by multiplying
10 x 10, for a magnification of 100X.
d. What is the total magnification of your microscope under low power? Use the
number printed on your low power objective and eyepiece: _________________.
e. What is the total magnification of your microscope under high power? Use the
numbers printed on your high power objective and eyepiece: ________________.
The objectives and eyepiece should be cleaned with lens paper at the beginning of
each laboratory period. Always use lens paper to clean lenses. Other types of
paper may scratch or smear lenses.
6. It is important to keep the lenses clean. The objectives and eyepiece should be cleaned
with lens paper only. Other types of paper may scratch or smear the lenses.
Part C. Preparation of a Temporary Wet Mount
Many of the slides you will use in this course will be wet mounts. You will make these slides
yourself. As the name “temporary wet mount” suggests, these slides are not permanent. A
temporary wet mount consists of some object placed in a drop of water on a slide with a
coverslip over the object. Use the following steps to prepare a wet mount of an insect wing.
Step 1. Add a small drop of water to a slide.
Step 2. Place the object to be viewed in the water drop.
Step 3. Position the coverslip at an angle to the slide. (Tweezers may be used to avoid
getting fingerprints on the coverslip.
Step 4. Lower the edge of the coverslip down slowly at an angle over the water drop
and object. This procedure will prevent trapping air under the coverslip.
Part D. Locating an Object Under the Microscope
1. Click the low power objective into viewing position. NOTE: Always locate an object
first with low power magnification even if a higher magnification is desired.
2. Place the wet mount on the stage of your microscope. Position the slide on the stage so
that the insect wing is directly over the center of the stage opening. Secure the slide
in place with the clips.
3. Look to the side of your microscope. Slowly lower the low power objective by turning
the coarse wheel adjustment until the objective almost touches the glass slide. Some
microscopes have an automatic stop that prevents lowering the objective onto the slide.
Other microscopes do not. CAUTION: Never lower the objective toward the stage while
looking through the eyepiece.
4. While looking through the eyepiece with both eyes open, slowly turn the coarse wheel
adjustment so the objective moves away from the stage. The insect wing should become
visible.
5. Bring the insect wing into sharp focus by turning the fine wheel adjustment.
Part E. Increasing the Magnification of the Microscope
1. Any object to be viewed under high power magnification is always located first under
low power and focused. Locate and center the insect wing under low power of your
microscope.
2. Move the low power objective out of viewing position. Look to the side of the
microscope and revolve the nosepiece. Click the high power objective into viewing
position.
3. Look through the eyepiece. The insect wing should be visible. However, it may need to
be focused. Use the fine adjustment wheel only to sharpen the focus. CAUTION: Never
use the coarse wheel adjustment for focusing with high power. Damage to the lens and
slide may result if the coarse adjustment is used.
4. If you are unable to find the insect wing, then do the following. While looking through
the eyepiece, move the glass slide slightly to the left, right away from, or toward you.
These movements may help to reposition the insect wing directly in the center of the high
power objective.
5. Repeat Parts D and E if you are unable to locate the object under high power.
Part F. Viewing a Prepared Slide
Two types of slides are used with the microscope: prepared slides and temporary wet mounts.
Prepared slides are permanent and are made to last a long time. The school usually purchases
these slides.
1. Obtain a prepared microscope slide from your teacher. Put the prepared slide on the
stage of your microscope and hold it in place with the stage clips. Position the slide
so that the object to be viewed is centered above the hole in the stage.
2. Begin with the low power objective in place. Watching from the side, turn the coarse
focus knob so that the objective is as close to the slide as possible without touching it,
or until the course adjustment knob will move no further.
3. Now look through the eyepiece at the object in the prepared slide and turn the coarse
adjustment knob so that the slide and objective are moving away from each other.
Focus as clearly as possible and move the slide so that the object is in the center of
the field of view.
4. Now use the fine adjustment knob to make the image appear even clearer.
5. In order to see more detail, use the high power objective. Rotate the nosepiece to
swing the high power objective into place, watching form the side to make sure that
it will clear the slide. It will be very close.
6. Bring the object into the clearest possible focus using only the fine adjustment knob.
CAUTION: Never use the coarse adjustment with the high power objective!!
Analysis
1. Match the microscope parts listed in Column I with their correct function in Column II.
Place your answers along the left side of Column II.
Column I
Column II
____ diaphragm
(a) allows light to pass through stage
____ stage opening
(b) brings objects into rapid but coarse focus
____ mirror or lamp
(c) regulates amount of light entering scope
____ eyepiece
(d) is attached to revolving nosepiece and contains a
lens capable of 10X magnification
____ low power objective
(e) holds glass slide and specimen in place
____ high power objective
(f) supports slide
____ revolving nosepiece
(g) directs light into scope
____ coarse wheel adjustment
(h) turns to change from one power to another
____ fine wheel adjustment
(i) contains a lens capable of 10X magnification
____ stage
(j) brings objects slowly into fine focus
____ stage clips
(k) contains a lens capable of 43X
6. Answer the following statements as true or false.
If false, change the wording to make it true.
a. _____ Total magnification of a microscope is determined by adding the eyepiece
lens magnification to the objective lens magnification.
b. _____ An object should always be located first with low power.
c. _____ A light microscope should be carried in an upright position with both hands.
d. _____ The fine wheel adjustment must be used to sharpen focus when using high
power magnification.
e. _____ Always look to the side of a light microscope when lowering the objective.
f. _____ Paper towels or newspaper may be used to clean the lens of a microscope.
g. _____ The eyepiece of a microscope is marked “10X.” The high power objective
is marked “50X.” The total magnification is 500X.