Lab #1
Name:______________________________
Microscopy – Cell Diversity and
Anatomy
INTRODUCTION
Even the technology of today cannot replace one of the most fundamental tools of
biology, the microscope. The microscope lets us see things that are otherwise too small for us to
see, and allows us study them. There are many different kinds of microscopes. The microscope
we will be using today is the compound light microscope. In this lab we explore how to use and
care for this most basic of biological tools.
We will then be using the microscope to gain a better understanding of cell structure.
Understanding the nature of cell structure and function is important to an understanding of
organisms. All living organisms are composed of cells, whether they exist as single cells, colonies
of cells, or in multicellular form. There are two general types of cells: prokaryotic and eukaryotic
– as was discussed in class. During this laboratory you will investigate some of the structural
characteristics of prokaryotic and eukaryotic cells. We are going to focus on the simple
differences between eukaryotes and prokaryotes in Bio 201. We will cover the prokaryotes in
much more detail in Bio 203.
PURPOSE
To learn how to use and care for the compound and dissecting microscope.
To learn the names of the parts of the microscopes.
To explore cell structure and morphology in prokaryotes and eukaryotes.
To obtain a better understanding of these terms: prokaryote, eukaryote, cell, cell
membrane, cell wall, nucleus, plastids, et al.
Give two general characteristics of prokaryotic cells.
Distinguish among the three morphological types of bacteria.
Describe the subcellular structure of a typical bacterium.
Identify cellular structures of a typical plant cell.
Identify cellular structures of a typical animal cell.
GENERAL INSTRUCTIONS
1. Work in pairs.
• If you do not have experience with a compound microscope, pair up with someone
who does.
• If you have experience with a compound microscope, pair up with someone who
does not.
2. Obtain microscopes from the microscope cabinets.
3. Calculating magnification (for the Compound Microscope):
• Multiply the power (magnification) of the eyepiece by the power of the objective lens.
• The power of the eye piece is 10x.
• The power of the objective lenses is written on them.
• Always include in any sketches the power or magnification under which you observed
the specimen. Always include the “x” as part of the magnification (e.g., 10x, 400x).
4. When finished, be sure that
• the scope is turned off.
• all slides are removed and returned to their proper container in the correct
orientation.
• the stage is wiped clean.
• the scope is set with the lowest power objective in place.
• the stage is lowered (objectives raised) as much as possible.
• the cord is properly wrapped.
• the scope is returned to the proper microscope cabinet.
PROCEDURES AND OBSERVATIONS
1. Obtain slide with a newspaper letter "e" mounted on it.
2. Determine how to use the microscope.
• Leave the microscope on low power – that means having the smallest lens in place.
It should already be set this way. What magnification is this? (see instructions above
for calculating magnification) ___________
• Answer the following questions to direct your exploration of the microscope. You can
find the names of the microscope on the diagram.
1) How do you turn the microscope on?
2)
What part of the microscope does the light come from?
3)
Where do you look into the microscope?
4)
Where do you put the slide?
5)
How do you focus? (Where are the focus knobs?)
6)
What happens on the microscope when you focus (what moves)?
7)
What do the two focus knobs do differently?
8)
Is the image of the "e" right-side up?
9)
How do you increase the amount of light? How do you decrease it?
10) How do you move the slide around without touching it?
11) If you move the slide to the right, which way does the image in the
microscope move?
12) If you move the slide to the left, which way does the image move?
13) If you move the slide up (away from you), which way does the image
move?
14) If you move the slide down (towards you), which way does the image
move?
3.
STOP HERE until instructed to continue. When everyone is ready, the instructor will go over
what you have learned so far.
4. The instructor will next instruct you on how to change the power of magnification on the
microscope, and how to focus.
• Increase magnification (power) to the next strongest lens. What magnification is
this? ____________
• Answer the following questions, again while still looking at the “e”:
1) What are the names of the parts of the microscope that change the
magnification?
2)
After you increase magnification, which focus knob should you use?
Why?
•
3)
After you increase magnification, is the image still in focus?
4)
Is it as bright as it was under lower power?
Now increase the magnification one more time, and observe the “e”. Make three
sketches of the “e”, one at each magnification.
Magnification
5.
STOP HERE until instructed to continue. When everyone is ready, the instructor will go over
what you have learned so far.
6. Return the “e” slide to its box, and obtain a “threads” slide.
• Observe under medium magnification. What magnification is this? ________
Are all three threads simultaneously in focus?_____________
•
Change the focus (remember, use only the fine focus knob!): focus in and out. What
do you observe?
•
How would focusing in and out help you to determine the three-dimensional structure
of a specimen? What order are the threads in (which is lowest, middle, and highest?)
7. Return the slide.
8. STOP HERE until instructed to continue. When everyone is ready, the instructor will go over
what you have learned so far.
Question: What is the difference between a compound and a dissecting microscope? What types
of samples would be appropriate for each type of miscroscope?
PART 2
PROCEDURES AND OBSERVATIONS
Part 2A: Prokaryotic Cells
Most prokaryotic cells are extremely small (approximately 1 to 2 m in diameter). Most are
heterotrophic, depending on preformed food, but some are autotrophic and make their own food.
Morphologically, bacteria are either round (coccus), rod-shaped (bacillus), or spiral-shaped
(spirillum). To view them with the compound microscope, you must use an oil-immersion lens
(100x objective). Even then, only their external features will be distinguishable.
Figure 2-1. The cells of many familiar genera of bacteria include the (a)
rod-shaped bacillus, (b) spherical coccus, and (c) helical spirillum.
It is possible to identify the three morphological types of bacteria (coccus, spirillum, and bacillus)
by observing their shape (Figure 2-1). You will also note that bacteria are often found in clusters
or in chains.
1. Examine the oil immersion demonstrations of prepared slides of the bacterial specimens set
up at the side of the room.
2. Draw simple sketches of these prokaryotes focusing on shape of the cells. Make the
sketches in the spaces below. For each, note whether the bacterium is spherical (coccus),
rod-shaped, (bacilus), or spiral-shaped (spirillum). Don’t forget to write in the magnification.
3. Now prepare a wet-mount of the dilute yogurt provided. Draw and label the bacteria you see
in this sample.
Specimen
Magnification
Shape
Specimen
Magnification
Shape
4.
Examining Cyanobacteria. Make a wet mount of the cyanobacteria species in the lab, as
instructed, and observe under high-dry power (highest power that is not oil immersion).
5. Draw a representative cell in the space below and label the parts which you can identify (but
don’t expect to be able to identify too much!!). Don’t forget to include the name of the
organism and the magnification.
Specimen: ________________________
Magnification: ______________________
Shape and Description: ________________
_______________________________
______________________________
Part 2B: Eukaryotic Cells
All eukaryotic organisms are composed of cells, whether they exist as single cells, colonies of
cells, or in multicellular form. Your body is composed of billions of cells, most of which are very
small, with specialized structures that allow for a diversity of functions. During this part of the
laboratory you will investigate the structures of plant and animal cells.
Examining Plant Cells
The cells of plants are eukaryotic, and contain both a membrane and a cellulose-based cell wall
that surrounds the plant cell. A large central vacuole surrounded by a membrane (the
tonoplast) is used for storing water, pigments, and wastes. Within the cytoplasm are
membrane-bound organelles unique to plants called plastids. In this lab, you will look at various
types of plastids responsible for photosynthesis (chloroplasts), for storing starch (amyloplasts
or leucoplasts) or for storing accessory pigments (chromoplasts). Chromoplasts contain
several types of pigment including carotenoids, which give plants an orange or yellow color.
1. Prepare a wet-mount slide of an Elodea leaf. Observe the thick cell wall, thinner cell
membrane, cytoplasm, nucleus, and chloroplasts. A large central vacuole should be
apparent. These structures characterize a generalized plant cell.
2. Sketch a representative Elodea cell as observed under high power, and label its parts.
Specimen: ________________________
Magnification: ______________________
Shape and Description: ________________
_______________________________
_______________________________
Do the chloroplasts appear to move?
Describe their movement.
6. Prepare a wet-mount slide of onion epidermal tissue. Onions (Allium) have layers of
modified leaves (scales) that can easily be separated from one another. Peel off a portion of
one layer and examine the concave side of the piece you have obtained. The surface is
covered by a thin layer of cells, the epidermis.
7. Remove a small piece of the epidermis (approximately 3 X 8 mm) by breaking the scale
gently, leaving the epidermis intact. Peel the epidermis from one of the halves of the scale.
Prepare a wet-mount slide of the isolated epidermis.
8. Observe the onion cells using low power (10X objective) and then high power (40X
objective).
9. If it is difficult to see the cells, add a drop of Lugol's solution (I 2KI) at the edge of the
coverslip. The iodine in the Lugol’s solution will stain starch blue/purple.
10. Sketch a representative onion cell as observed under high power, and label its parts.
Specimen: ________________________
Magnification: ______________________
Shape and Description: ________________
_______________________________
_______________________________
11. Compare the onion cell with the Elodea cell. Since they are both plant cells, they should be
similar. You will note that onion cells lack one structure (organelle) that is very conspicuous in
Elodea cells. What is this organelle missing in the onion cells?_______________________
List the similarities and differences between Elodea cells and onion cells.
Similarities
Differences
12. Prepare a wet mount slide of a potato. Use a razor blade to slice a piece of tissue, as thin
as possible, from a potato. Be careful not to cut your fingers. Prepare a wet-mount slide; use
a drop of water.
13. Study the slide at low power (10X objective) and then at high power (40X objective). Add a
drop of Lugol's solution (I2KI) to the side of the coverslip and observe the cells as the iodine
solution makes contact with them.
Specimen: ________________________
Magnification: ______________________
Shape and Description: ________________
_______________________________
_______________________________
How does the reaction of iodine with the potato cells compare with what you observed in your
onion epidermis preparation?
What does this tell you about the differences between the storage products in onions and
potatoes?
Do you see any chloroplasts?
Why or why not?
You will probably see some small oval-shaped blue-black structures. These leucoplasts
store starch. Why did they turn blue?
13. Prepare a wet mount slide of carrot or red pepper. Use a razor blade to slice a piece of
tissue, as thin as possible, from the outer portion of a peeled carrot, or scrape some tissue from a
red pepper. Prepare a wet-mount slide using water.
Can you see the chromoplasts? Sketch them.
Specimen: ________________________
Magnification: ______________________
Shape and Description: ________________
_______________________________
_______________________________
Question: Briefly describe the function of chloroplasts, amyloplasts, and chromoplasts. Explain
why these structures were seen only in particular plant cells.
Examining Animal Cells
Animal cells can be studied using the light microscope, but most of the cellular organelles within
the cytoplasm are not visible without the use of special staining techniques. The nucleus and
nucleolus, where ribosomes are manufactured, are usually apparent in most cells.
To study the structure of animal cells you will use prepared slides of animal tissues. These are
collections of cells that have a similar function. The cells are usually organized into sheets.
1.
Prepare a wet mount slide of your cheek cells. You will examine cheek cells obtained
from your mouth. Instructions for obtaining and staining the cheek cells will be provided by
your instructor. Sketch a few cells, and label the plasma membrane, nucleus, and cytoplasm
Specimen: ________________________
Magnification: ______________________
Shape and Description: ________________
_______________________________
_______________________________
Do the cells you observe have a cell wall?
Plastids?
Chlorophyll?
List the similarities and differences between the plant cells and the animal cells you have
observed.
Similarities
Differences
Clean-up of compound microscope
1. When finished, clean up the compound microscope and prepare it to be put back in the
cabinet, as instructed on the 1st page of this lab:
• the scope is turned off.
• all slides are removed and returned to their proper container in the correct
orientation.
• the stage is wiped clean.
• the scope is set with the lowest power objective in place.
• the stage is lowered (objectives raised) as much as possible.
• the cord is properly wrapped.
• the scope is returned to the proper cubicle in the proper microscope cabinet.
2. Have the instructor come and take a look at your microscope to be sure you have
correctly prepared it to be put away. If it is correctly prepared, the instructor will put
his/her initials here:
3. After the instructor has checked you, you may put the microscope away.
TO TURN IN: This lab report will be due on Thursday (6/29). Answer all the questions posed in
the proceeding pages. If you need additional space, please use a separate page. Also include all
drawings as indicated.