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Laboratory Activity 3 – REVIEW ON THE USE OF THE MICROSCOPE

INTRODUCTION
The microscope is an essential instrument that can help view structures which are too small to be seen
by the naked eye. There are major kinds of microscope designated as light or electron microscope. The
light microscope use series of lenses and visible light or ultraviolet rays to illuminate specimen. The
electron microscope use electron beams and magnets to observed subatomic particles. Among the two
kinds of microscope, light compound microscope will be used throughout the laboratory activities. It is
called compound microscopes since the instrument contains two lenses – one is located in the eyepiece
and the other lens is located in the objective. In this activity, as gain knowledge in using the microscope
you will understand how precise the instrument is and valuable for studying microorganism.

OBJECTIVES
1. To study the important parts and function of the microscope.
2. To learn how to focus and use the microscope to study microscopic organisms and cells.

MATERIALS
Compound Microscope
Letter e slide, cheek cell smear kits

CONTENT
A. Parts of Compound Microscope
1. Look at the microscope and examine its parts. The compound microscope is divided into three
major divisions; 1. Mechanical; 2. Illuminating and 3. Magnifying parts.
2. The mechanical parts function to support the other parts of microscope and adjust the
illuminating and magnifying parts. It is composed of the following parts:
a. Base – a flat platform located at the bottom which supports the entire microscope.
b. Arm – a curved frame above the pillar that provide attachment for stage and body tube. This
is also the part wherein you can hold the microscope when transporting or moving it.
c. Revolving nosepiece – a round plate frame located at the bottom of the body tube. This
serves for the attachment of 3 to 4 objectives. This also rotates to allow shifting of objectives
from one type to another.
d. Adjusting knobs – two round knobs that functions to raise the body tubes and objectives. The
two knobs are the following:
i. Coarse adjustment knob – A larger screw or knob that brings object in focus. It allows
coarse movements of the body tube.
ii. Fine adjustment knob – smaller screw or knob that brings the object to sharper focus. It
allows fine or smaller movement of the body tube.
e. Stage – a small square piece that extends between the upper lens and lower devices for light.
It has a hole in the center that permits light to pass into the lens. It is called mechanical stage
since it has adjustment knobs located at the side of the stage which is used to move the slide
in vertical and horizontal directions on the stage.
 f. Iris diaphragm – regulates the amount of light that reaches the condenser
3. The other parts of microscope belong to the illuminating parts that serve as the source of light
and regulate or concentrate the amount of light that passes to the specimen. It is composed of
the following parts:
a. Mirror – a round glass that reflects light coming from natural or artificial sources. In this
microscope, it uses a light bulb that produces the light. The switch for the bulb is located at
the side of the base of the microscope. On the other side of the base there is a knob that
regulates the intensity of light produced by the bulb.
b. Condenser – a round lens located below the stage and set at the stage aperture. This serves
to collect and concentrate the light coming from the source. The amount of light admitted in
the condenser is regulated by an iris diaphragm which has a lever that serves as a knob in
operating the diaphragm.
4. The last portions of the microscope are the magnifying parts that serve to enlarge the object or
specimen being viewed. It is composed of the following parts:
a. Eyepiece or Ocular – located at the tip of the draw tube. It contains a lens that helps to
magnify the specimen and projects a virtual image. This part also serves for viewing the object
or specimen being observed. Has 10x magnification power.
b. Objectives - it also contains lens to magnify the specimen and projects a real image. In this
microscope, it is composed of four objectives:
i. Scanner – a tube with large diameter of lens; 4x
ii. Low power objective (LPO) – a longer tube with large diameter lens; 10x
iii. High power objective (HPO) – a shorter tube with small diameter lens; 40x
iv. Oil immersion objective (OIO) – a shorter tube with fine diameter of lens; 100x
The four objectives in this microscope have a thin strip color for you to easily identify the four
objectives. The scanner has red color; low power has a yellow color; high power has a blue
color and the oil immersion has a white color.

B. Using the microscope

Now that you are familiar with the parts and function of the microscope, the next step that you will do is
how to focus and use the microscope in studying minute organism (microorganism).
1. Get a prepared slide provided by your instructor. Place the prepared slide securely on the stage.
Position the smeared part on the slide at the stage aperture so that the light coming from the
condenser passes through the smear area.
2. Bring the scanner into vertical position aligned with the body tube. If the objective is not set at
scanner, slowly rotate the revolving nosepiece until the scanner clicks in place.
3. While looking at the side of the microscope, move the objective downward by turning the coarse
adjustment knob clockwise. Adjust the distance between the objective lens and the stage to
about half an inch.
4. Carefully raise the objective by turning the coarse adjustment counterclockwise until the outline
of the object is clear and sharp. NEVER lower the objective or decrease the distance between the
objective lens and the slide while looking through the ocular or eyepiece. If the specimen is not
centered, move the slide slowly to bring the image into the center of the field.
5. Observed the size of the organism and draw it. Do the same procedure with low power (LPO) and
high power objective (HPO).
6. After focusing under the LPO and HPO, shift the objective to an oil immersion. Using the oil
immersion objective, place a drop of oil on the cover slip of the prepared specimen. Slowly move
down the objective until the lens of the oil immersion objective touches the drop of oil. Look
 through the ocular and slowly turn the fine adjustment until the image is clear. Draw the organism
observed under the oil immersion objective.
7. For your observation and drawing, place your drawings in the student report sheet of this
laboratory activity. Answer the review questions after you’re done with your drawing and writing
your observation.
8. After you finished your observations, remove the slide from the stage and gently clean the oil
from the slide and objective lens using a lens cloth or lens paper.

Do’s and Don’ts When Using the Microscpe

DO’s DON’Ts
Always carry the microscope with one hand Do not swing the microscope, do not drag or bang
grasping the arm of the microscope and the other it across the countertop or bench top.
hand supporting the bottom of the microscope
base.
Wash your hands before handling the slides to Never place the microscope near the bench’s edge
avoid transferring finger grease to the slides. and keep electric cords out of the way, towards
the center of the bench.
Use only lens paper to clean the lenses of the Do not clean the lenses with bath tissue or other
eyepiece and the objectives. fibrous materials because these could scratch the
lenses.
To remove dirt from the eyepiece, breathe on the Never rub the lenses of the objectives with dry
lens and GENTLY wipe off the condensation with lens paper or other materials.
lens paper.
To remove oil from the objectives, moisten a piece Never attempt repair a microscope or force and
of lens paper with ethyl ether and slowly draw the adjustment knob. You may severely damage the
wet paper across the front surface of the lens. instrument.
Microscopes in the laboratory are parfocal, DO NOT LOWER THE STAGE WHEN MOVING
meaning, the objects in focus remain in focus as FROM ONE OBJECTIVE TO ANOTHER. You will lose
you change from one objective lens to another. the image.
Thus, USE only the fine adjustment knob to fine
tune your image after you transfer from low
power to high power.
Examine your material first using the scanning NEVER RAISE THE STAGE WHILE YOU ARE
objective (4x); then proceed to the next higher FOCUSING USING THE COARSE and FINE
objectives, i.e. LPO and HPO. Carefully rotate the ADJUSTMENT KNOBS.
revolving nosepiece when shifting the objectives.
You will feel a click which indicates that the
objective is completely aligned.
Replace and remove a slide only after the lowest Do nor forget to unplug the power cord of the
power objective have been rotated into viewing microscope; bring down the stage and out the 4x
position. (scanning) objective in position.
 LAB ACTIVITY

PROCEDURES:

A. Manipulation of the Microscope

1. Obtain a letter “e” prepared slide.

2. Place the slide on stage; steady it on the stage with the stage clips. Make sure the label of the slide is
facing towards you.
3. Focus the slide at 4x objective. How does the letter “e” appear?
4. Draw the letter “e” exactly as how you see it. Compute for the total magnification.

Total magnification = (magnification of the eyepiece) x (magnification of objective lens used)

If your drawing is smaller or bigger than the actual specimen, you have to compute for the change in
the magnification.

Size of the drawing

Macroscopic magnification =
Size of the specimen
5. Change the magnification to 10x objective. Did you see all the letter “e”? How much of the field of
view do you see? Draw the specimen. Compute again the total magnification.
6. Change the magnification to 40x objective. How much of the letter “e” can be seen? Draw the
specimen. Compute again the total magnification.
7. Take out the slide and place it again on the stage to focus at 4x objective. This time the label of the
slide should be upside down. How does the letter “e” appear? Why do you think is the view like that?
Draw the specimen and provide the total magnification.
8. When done, take out the slide. Set the objective at 4x; lower down the stage, and return the
microscope and slide specimen.

B. Cheek Cell Fresh Mount

1. Get a clean slide and a cover slip and secure them on your table.
2. Using the broader end of a toothpick, gently scrape the inside of your cheek to collect the epithelial
cells.
3. Smear the collected cells on the glass slide.
4. Put a drop of methylene blue stain to color the smear (otherwise they will be clear and difficult to
see).
5. Wash off the excess stain from the smear by indirectly dropping water on a slanted glass slide.
6. Air dry and wipe off excess water, then place the coverslip on the smeared cells.
7. Observe the slide under the microscope in LPO and HPO.

You are looking for light colored blobs with dark spots in them. Perfect circles with black outlines are air
bubbles; do not draw them. Draw the cells under high power objective. Label the visible parts and
structures of the cell (nucleus, cytoplasm, and cell membrane).

C. Onion Skin Fresh Mount

Onion Skin Cell Fresh Mount

1. Get a clean slide and a cover slip and secure them on your table.
2. Get an onion and remove a layer from the bulb.
3. With the forceps, remove the inner layer of the epidermis from the concave surface of the onion.
4. Place the peeled epidermis on the center of a clean glass slide and place a drop of dilute iodine
solution.
5. Using a toothpick, spread flat and straighten out any folds of the onion epidermis.
6. Carefully, place the coverslip over the onion skin smear. Make sure there is no air bubbles on the
mount.
7. Place the slide on the microscope and observe it first under LPO, then proceed to HPO.

Note the arrangements of the cells and their shape. Draw the cells under high power objective. Label
the visible parts and structures of the cell (nucleus, cytoplasm, and cell wall).
 RESULTS AND DISCUSSION:

Total Magnification (TM): __________________ Total Magnification (TM): __________________

Observation: Observation:

Total Magnification (TM): __________________ Total Magnification (TM): __________________

Observation: Observation:
 Cheek Cells

Total Magnification (TM): __________________

Observation:

Onion Skin Cells

Total Magnification (TM): __________________

Observation:
CONCLUSION

QUESTIONS

1. Why is it important to begin focusing with the scanning objective?

2. If you bump your microscope and lose focus, what do you do to refocus your specimen?

3. Why must you center your image before switching to a higher objective?

4. Explain why the stage of the microscope should not be raised while looking through the ocular
lens.