Name: ______________________________________Period: _____________________ Date: ______________________
Introduction to the Compound Light Microscope
Background:
Microscopes are very important tools in biology. The term microscope can be translated as “to view the tiny,” because
microscopes are used to study things that are too small to be easily observed by other methods. The type of microscope
that we will be using in this lab is a compound light microscope. Light microscopes magnify the image of the specimen
using light and lenses. The term compound means that this microscope passes light through the specimen and then
through two different lenses. The lens closest to the specimen is called the objective lens, while the lens nearest to the
user’s eye is called the ocular lens or eyepiece. When you use a compound light microscope, the specimen being studied
is placed on a glass slide. The slide may be either a prepared slide that is permanent and was purchased from a science
supply company, or it may be a wet mount that is made for temporary use and is made in the lab room.
Objectives:
1. Learn the parts of a compound light microscope and their functions.
2. Learn how to calculate the magnification of a compound light microscope.
3. Learn how to make a wet mount slide.
4. Understand how the orientation and movement of the specimen’s image changes when viewed though a compound
light microscope.
5. Learn the proper use of the low and high power objective lenses.
6. Learn the proper use of the coarse and fine adjustments for focusing.
Materials:
Compound Microscope
Water
Methyl Blue
Microscope Slides
Prepared Slides
Glass Cover Slips
Toothpicks
Pipette
Paper Towels
Part 1: Compound Microscope Parts and Function
1. Identify the parts on your microscope and determine the function of each part. Use the words from the word
bank below to fill in the names in Table 1 below.
Word Bank:
Arm
Base
Coarse adjustment
Diaphragm
Fine adjustment
Objective lenses
Ocular lens
Light
Stage
Stage clips
Figure 1: Compound Light Microscope
Table 1: Microscope Part and Function
Part
A
B
C
D
E
F
G
H
I
J
Name
Function
2. The magnification is written on each objective. The total magnification using the lenses can be determined by
multiplying the ocular lens with the objective. Use this information to fill in the following chart.
Table 2: Microscope Lens Magnification
Lens/ Objective
Magnification
Total Magnification
Ocular/ Eyepiece
Scanning Objective
Low Power Objective
High Power Objective
Part 2: Using a Compound Microscope
3. Place the slide of the "letter e" on the stage so that the letter is over the light source and is right side up. Use the
scanning objective to view the letter and use the coarse knob to focus. Repeat on the low power objective.
Finally, switch to high power. Remember at this point, you should only use the FINE adjustment knob.
4. Draw the "e" as it appears at each magnification. Drawings should be drawn to scale and you should note the
orientation of the e in the viewing field (is it upside down or right side up?)
SCANNING
LOW
Have your partner push the slide to the left while you view it through the lens.
Which direction does the “e” appear to move? __________________
HIGH
5. Obtain a slide with three different colored threads on it. View the slide under scanning and then low power. You
should note that you could only focus on one colored thread at one time. Figure out which thread is on top by
lowering your stage all the way, then slowly raising it until the thread comes into focus. The first thread to come
into focus is the one on top.
Which color thread is on top? _____________
Which color thread is in the middle? ______________
Which color thread is on the bottom? ____________
Part 3: Preparing and Viewing a Wet Mount- Human epithelial cells
6. Obtain a clean microscope slide.
7. Place a small drop of water on the slide. This is the “wet” part of the wet mount.
8. Gently rub a toothpick on the inside of your cheek, and then swirl the toothpick in the water on the slide.
9. Use Methyl Blue to stain the cells. When you reach this step, alert your teacher who will give you a drop of
Methyl Blue.
10. Place a cover slip over the specimen. This will sandwich the specimen between the slide and the cover slip. To
avoid trapping air bubbles, set one edge of the cover slip on the slide, and then let the rest of the cover slip drop
SOFTLY. As it drops from one side to the other, air will be pushed out, and this will reduce the number of
bubbles in the wet mount. Use a paper towel to blot the outside edges of the coverslip.
11. The cheek cells are now ready to be viewed through the microscope. Once the slide is positioned on the
microscope stage, start at a low power magnification, and work up to the level of magnification required to get a
detailed view of the specimen.
12. Draw what you see at each magnification. Drawings should be to scale.
SCANNING
LOW
HIGH
Post Lab Questions
1. Answer true or false to each of the following statements
__________ On high power, you should use the coarse adjustment knob.
__________ The diaphragm determines how much light shines on the specimen.
__________ The low power objective has a greater magnification than the scanning objective.
__________ The fine focus knob visibly moves the stage up and down.
__________ Images viewed in the microscope will appear upside down.
__________ The type of microscope you are using is a scanning microscope.
__________ For viewing, microscope slides should be placed on the objective.
__________ In order to switch from low to high power, you must rotate the revolving nosepiece.
__________ The total magnification of a microscope is determined by adding the ocular lens to the objective lens.
2. Why should you always begin to use a microscope with the low-power objective?
__________________________________________________________________________________________________
__________________________________________________________________________________________________
3. Why should you only use the fine adjustment when the high-power objective is in position?
__________________________________________________________________________________________________
__________________________________________________________________________________________________
__________________________________________________________________________________________________
4. Why must the specimen be centered before switching to high power?
__________________________________________________________________________________________________
__________________________________________________________________________________________________
__________________________________________________________________________________________________
5. If you placed a letter “g” under the microscope, how would the image look in the field of view?
__________________________________________________________________________________________________
__________________________________________________________________________________________________
__________________________________________________________________________________________________
6. If a microscope has an ocular with a 5x power, and objectives with powers of 10x and 50x, what is the total
magnification of: (Show your math for full credit!)
a. low power? _______________________________________________________________________________
b. high power? _______________________________________________________________________________
7. If you are looking through a microscope at a freshly prepared wet mount and you see several perfect circles that are
completely clear surrounding you specimen, what is the most likely explanation?
__________________________________________________________________________________________________
__________________________________________________________________________________________________
__________________________________________________________________________________________________