Name: ___________________ Class: ________ Date: _____________
Hooke’s World – A Microscopic View
Pre-lab: The compound microscope is probably one of the most useful tools available to
biologists. Many discoveries have been made in the past through its use. During the
laboratory activity you will learn about the microscope, its proper use and care, and certain
basic skills and techniques needed to make your microscopic work more efficient.
There are several items that will be covered in this lab. You will learn:
 Name and give the function of 12 basic parts of a light microscope.
 List three major characteristics of microscopes and explain how these vary in an
electron microscope and light microscope.
 Describe how the microscope affects images: inversion and depth of field.
 Calculate the total magnification of high, medium and low power.
 List the steps used to bring an object into focus.
 Identify three types of cells studied in this exercise and state three differences
between plants and animal cells.
I. Parts of the Microscope:
1
A. ocular (eyepiece) – consists of a set of lenses at the top of the microscope. The
magnification of the ocular is stamped on the lens. For example, a lens marked 4X has 4
times the magnification and makes the objects seen through it look four times their actual
size.
B. Body tube assembly – a hollow tube through which light passes from the
objectives on the bottom to the ocular on the top.
C. Revolving nosepiece – holds the three or four set of lenses (objectives). As you turn
the nosepiece it clicks into different positions, which indicates when each objective is
properly aligned for viewing.
D. Objectives – the most delicate and costly parts of your microscope.
Lower power objective (shortest) magnifies 4x (scanning)
Medium power objective magnifies 10X – great detail
High power objective (longest) magnifies 40X – greater detail
E. Mechanical Stage – holds and supports the microscope slides and some microscopes
include a stage back and forth travel knob and a stage lateral travel knob.
F. Diaphragm – controls the amount of light that illuminates the viewed object.
G. ARM – supports the upper parts of the microscope and provides a handle to carry the
microscope.
H. Base – the flat bottom part upon which the microscope rests
I. Light source – an attached lamp that directs a beam of light up through the object
J. Coarse adjustment knob – used to bring objects into focus, used only with low power
objective
K. Fine adjustment knob – used to bring objects into final view
II. How to Focus the Microscope – Low Power


With the coarse adjustment knob, raise the nosepiece until it stops.
Place a slide of the letter e on the stage and use the clips to secure it. Center the
e as best you can on the stage.





Using the 4X objective, decrease the distance between the stage and the nose piece
until the nosepiece is about 1/8 inch above the slide
Look into the ocular, and adjust the diaphragm to give the maximum amount of light.
Use the course adjustment knob and bring the letter e into focus
Once the object is seen, it may be necessary to adjust the amount of light using the
diaphragm. This can also create shadows.
Use the fine adjustment knob to sharpen the focus.
2
III. How to Focus the Microscope – High Power
Compound light microscopes are parfocal – meaning that once an object is in focus
with low power, it should be in focus with high power.


Bring the letter e into focus under low power by following the previous instructions.
Move the 10X objective into place by turning the nosepiece.
If any adjustment is needed, use only the FINE adjustment knob. High powered
objectives are to only be used with the FINE adjustment knobs.
Draw a circle around the portion of the letter e that you see with the 10X
objective.
Move the 40X objective into place by turning the nosepiece.
Adjust and focus the e using only the FINE adjustment knob.

Draw a circle around the portion of the letter e that you see with the 40X.

When you are finished observing the letter e, rotate the nosepiece until the low
power objective (4X) clicks into place and then remove the slide from the stage.




IV. The following Rules should be observed:








Have both eyes open when looking through the eyepiece.
The low power objective should be in position at the beginning and the end of
each use.
Use only lens paper to clean the lens.
Do not tilt the microscope.
Keep the stage clean and dry to prevent rust and corrosion.
Do not remove parts of the microscope.
Keep the microscope dust free by covering it.
Report any malfunctions immediately. Do not try to repair microscopes on your
own.
V. Total Magnification
Total Magnification is calculated by multiplying the objective lens magnification by
the magnification of the ocular lens.
10X
times
5X
equals 50 times magnification
(answer questions on your worksheet)
VI. Diameter of Field
Place a prepared millimeter scale slide and mount it on your microscope stage so that the
inner edge of the ruler is visible as horizontal line along the diameter of the low power field.
Be sure to look at the millimeter side of the ruler. Estimate the number of millimeters to
the tenths. Do the same with the medium powered objective and the high powered
objective.
3
VII. Cell Structure
Making a wet mount
(Originally in Anderson, P., and Mader, S.:General Biology. Dubuque, Iowa: Kendall/Hunt Publishing Company, 1973)
It is often necessary to prepare a specimen for observation under a microscope. The
object should be viewed as a wet mount. To prepare a wet mount place it directly on the
slide and add a drop of water or stain. The mount is then covered with a cover slip. The
cover slip helps contain the specimen and keep the objective lenses clean.
A. Onion Cells
Onion’s have an epidermal layer found on the inside of each layer of an onion bulb. It
appears as a thin, almost transparent membrane and can be removed by using your fingers.
Remove a small piece of this epidermal tissue and place gently on a clean glass slide. Add a
drop of Lugol’s solution or iodine stain. Place a cover slip over the tissue and observe. If
too much stain is on the slide, you can place a small piece of paper towel beside the cover
slip; this will draw the excess stain off. Dispose of paper towel in the trash immediately.
Be careful not to get stain on our hands or clothing.
4
Examine the wet mount under low power of your microscope. Restrict light with the
diaphragm and observe the cell walls. The plasma membrane is located just inside the cell
wall. Locate the nucleus and cytoplasm.
B. Elodea Cells
Elodea is a green aquatic plant with leaves that are ideal for microscopic viewing. The green
color is due to the presence of the chlorophyll pigment, which is essential in the process of
photosynthesis.
Obtain a clean, dry slide. Remove a young leaf from the actively growing tip of Elodea.
Place the leaf in a small drop of water on your slide and carefully add the cover slip.
Locate the nucleus, cell wall, and cytoplasm. Switch to high power and observe the
chlorophyll that is contained in the chloroplasts. Carefully observe the chloroplasts in one
cell. Are they moving?
5
C. Human Epidermal Cells
Now it is time to observe your own cells, squamous epithelium cells from the lining of your
cheek. Gently scrape the inside of your cheek with a clean, flat toothpick and place the
scraping into the drop of water on the slide and add a drop of very weak methylene blue and
add a cover slip.
Observe under the microscope with low power. You may have to search for your epithelial
cells, but should be easy to find. When they are located, switch to high power and observe
the plasma membrane, cytoplasm, and nucleus. Is a nucleolus present?
D. Pond Water
Examine a drop of pond water. Make a wet mount of pond water by taking a drop
from the bottom of the container. To locate any organisms present, scan the slide: start at
the upper left corner and move the slide forward and back as you work across the slide
from the left to the right.
Use the pictorial guides provided to try and identify three different organisms. Be sure to
use low, medium and high power objectives as needed.
6
Name ________________________ Class _______ Date __________
Handouts are to be turned in for a grade.
I. LABEL THE MICROSCOPE
7
II and III. HOW TO FOCUS THE MICROSCOPE – LOW POWER/HIGH
POWER
1.
In the space provided, draw the letter e as it appears on the slide (not through
the eyepiece).
2.
Draw the letter e as it appears when you look through the eyepiece.
Magnification ___________
3.
What differences do you notice?
4. Move the slide to the right. Which way does the image appear to move?
IV. The following Rules should be observed:
What objective lens should always be in placed at the beginning and ending of looking at a
slide?
8
V. Total Magnification
Ocular Lens
Objective Lens
Total Magnification
Lower Power
______________X
_______________=
______________
Medium Power
______________X
_______________=
______________
High Power
______________X
_______________=
______________
VI. Diameter of Field
What is the diameter in millimeters of the low power field of view? ______________
What is the diameter in mm of the medium power field of view? ____________
What is the diameter in mm of the high power field of view? _____________
VII. Cell Structure
A. Onion Cells
Draw and label the visible parts of an onion cell.
Estimate how many onion cells stretch
across the low power field. ____________
Magnification ___________
Knowing the diameter of the field as calculated
above, decide the length of each onion cell .
______________________________
9
B. Elodea Cells
Draw and label the visible parts of an Elodea plant cell.
Estimate how many elodea cells stretch
across the low power field. ____________
Does this cell have a plasma membrane?
_______________________________
Magnification ____________
Observe the chloroplasts. Are they moving? Explain
________________________________
________________________________
________________________________
C. Human Epidermal Cells
Draw and label the visible parts of human epidermal cells.
Is a nucleolus present?
Magnification ____________
10
What are the differences between plant and animal cells?
PLANT CELL
ANIMAL CELL
Shape
Cell Wall
Other
D. Pond Water
Draw three different living organisms you observed in pond water.
Magnification ____________
Magnification ____________
Magnification ____________
11