Name: ______________________
Block: ______
Microscope Lab
Introduction: In almost every type of biological research, the
microscope plays a fundamental role. Scientists in each field rely on it
to study the fine structures of cells and tissues – things too small to
see with the unaided eye. Were it not for the microscope, our
understanding of life would be far different from what it is today.
In this lab, you will learn how to use a compound light microscope to
observe structures too small to see with the unaided eye. In future
labs, you will observe microscopic organisms using the techniques you
learned in this lab.
Prelab Preparation: It is essential to learn how to use and care for your
microscope properly. This is why we have studied the diagram of the
microscope and learned the names of all of its parts.
Your microscope is expensive and fragile. It is important for you to use it
correctly to avoid damaging it and to avoid breaking slides or
destroying specimens. When you are using your microscope, it should
rest securely on your table, away from the edge. When you carry your
microscope, ALWAYS use 2 hands. Hold its base with one hand and its
arm with your other hand.
Always use an appropriate light sourced. If your microscope has a lamp,
plug it in and turn the lamp on. If your microscope has a mirror, adjust
it to get a good amount of light through the eyepiece. Make sure the
diaphragm is sufficiently open so enough light can get through.
The purpose of the microscope is to magnify your specimen. Microscopes
use 2 lenses – the eyepiece and an objective. (The magnification of
each lens is written on the lens case.) If the eyepiece is 10x and the
low power is 10x, then the magnification under low power is 100x. In
equation form, this is written:
(eyepiece magnification) x (objective magnification) =
total microscope magnification
Pre-lab Question:
1. If the magnification of the eyepiece is 10x and the magnification of
the high power objective is 40x, what is the total magnification
under high power?
Procedure:
Part A. Orientation of the Image
1. Place a prepared slide with the letter e on the stage.
2. With the medium-power objective in the light path, position the
slide with the specimen (the letter e) right side up on the stage,
center the specimen in the field of view, and carefully bring it into
focus.
3. Draw in the circle below, the image of the e as you see it through
the eyepiece. Record the total magnification used in the line below
the circle.
Drawing of the letter e as seen
through the ocular _____x
Part A Questions:
A. Is the image right side up or upside down compared to the
specimen?
B. Compared to the specimen, is the image backward?
C. Move the specimen to the right while watching it through the
microscope. In which direction does the image move?
D. Move the specimen away from you. In which direction does
the image move?
4. Remove the slide and return it to the front.
Part B: Depth of Field
The depth of field is the distance through which you can move the
specimen and still have it remain in focus. Remember, the working
distance – the space between the objective lens and the cover slip –
decreases with increasing magnifying power. Therefore, the higher the
power of the objective in use, the closer the objective is to the slide –
and the more careful you must be.
1. Obtain a slide with 3 cross colored threads. Once you have the
threads in focus (using first the low-power objective and then the
medium-power objective). Then try focusing with the high-power
objective.
A. How many threads are in focus using the
low-power objective ________
medium-power objective ________
high-power objective _______
B. With which objective is it easiest to focus a specimen?
C. At which magnification is it most difficult to focus a
specimen?
Part C: Cheek Cell Lab
1. Use the Low Power (red) objective to focus. You probably will not
see the cells at this power.
2. Switch to Medium Power (yellow). Cells should be visible, but they
will be small and look like nearly clear purplish blobs. If you are
looking at something dark purple it is probably not a cell.
3. Once you think you have located a cell, switch to High Power (blue)
and refocus. (Remember do NOT use the coarse adjustment knob
at this point.)
4.
---Sketch the cell at low and high power. Label the nucleus, cytoplasm,
and cell membrane. Draw your cells to scale.
Low
Medium
High
Use your book pages 151-155 to answer the following questions:
1. Who was the first person to discover the cell?
2. What was he looking at when he discovered the cell?
3. How powerful was his microscope? How powerful was your
microscope at each objective?
4. How does a cell’s size affect the cell’s function?
5. What is the difference between a Eukaryotic Cell and a Prokaryotic
Cell? What is the cheek cell? (Eukaryotic or Prokaryotic)