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Exercise 5- The Microscope and Cell
Exercise 5
THE MICROSCOPE AND THE CELL
Student Learning Outcomes:
At the completion of this exercise you should:
(1)
Be able to label a compound microscope diagram indicating its 12 basic parts.
(2)
Be able to describe how to adjust a microscope in order to observe a cell under scanning,
low, and high power magnifications.
(3)
Be able to estimate the size of a cell or other object, in millimeters and microns, under
high and low power magnifications.
(4)
Be able to identify the cell membrane, nucleus, and cytoplasm of an animal cell. Be able
to identify the cell membrane, nucleus, and cytoplasm of a plant cell.
(5)
Be able to define the basic biological concept of complementarity of structure and
function.
(6)
Be able to describe examples of the complementarity of structure and function using
animal epithelial and adipose cells as well as vascular bundle cells in plants.
(7)
Be able to draw three dimensional diagrams of both animal epithelial and adipose cells as
well as plant vascular bundle cells.
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Exercise 5- The Microscope and Cell
I.
The Microscope
Introduction
When many people hear the word biology, they picture a person looking through a microscope, and
students entering a beginning biology course often expect to use the microscope a great deal. In practice,
whether a professional biologist regularly uses a microscope depends on his/her area of special interest.
Nevertheless, it is a valuable tool with which all biologists are familiar. When using a microscope, we
should remember this: it is only an extension of our eyes which allows us to examine individual cells and
other structures which are otherwise too small to be seen. Today we will develop the basic microscope
skills necessary to successfully study cells in this and some of the subsequent laboratory exercises this
semester.
A. The Compound Microscope
The compound microscope, one of the two types of microscopes you will use in this class, must be cared
for and operated correctly. You should spend considerable time during this period learning how to use it,
and you should pay particular attention to how it differs in form and function from the dissecting
microscope. See Figure 1. One of the major differences between the two microscopes is that the
compound microscope has higher powers of magnification than does the dissecting microscope. All
specimens to be viewed and studied with the compound microscope must be mounted on a glass slide and
covered by a coverslip. (Since objects viewed through the dissecting microscope are usually larger,
coverslips are not often used.) The correct technique of mounting a specimen on a slide will be
demonstrated.
Procedure:
1.
The proper way to carry the compound microscope will be demonstrated. Always use two hands.
Make sure that the cord is not dangling to prevent a tripping hazard. One hand should be holding the base
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Exercise 5- The Microscope and Cell
of the microscope, while the other should hold the arm of the microscope.
Figure 1. General diagram of a binocular compound microscope.
Always remember that the microscope is a delicate instrument. Please care for it and use it
correctly.
Practice the Parts of the Compound Microscope.
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Exercise 5- The Microscope and Cell
In order to practice for your upcoming quiz, locate and identify the following parts of the compound
microscope on the diagram below. See your microscope and Figure 1 for help. (You should learn these
terms before proceeding.)
1.
2.
3.
4.
5.
6.
OCULAR or Eye Piece
○ Contains lenses to increase
magnification
○ May be replaced with another of
lower or higher magnification
BODY TUBE
○ Holds lenses of ocular and
objectives at the proper working
distance from each other
NOSEPIECE
○ Permits interchange of scanning,
low, and high power objectives
OBJECTIVES
○ Contains lenses of different
magnifications
SLIDE (SPECIMEN) HOLDER
○ Mechanical stage with adjustment
knobs
STAGE
○ Supports slide over opening that
admits light from mirror or lamp
7.
CONDENSOR & IRIS DIAPHRAGM
○ Concentrates & focuses light
○ Regulates amount of light passing
through the specimen
8. LIGHT SOURCE
○ Directs light upward through
diaphragm and hole in stage
9. COARSE ADJUSTMENT
○ Moves stage up and down
approximately to the correct
distance
10. FINE ADJUSTMENT
○ Permits exact focusing by moving
stage up or down very slightly
11. ARM
○ Supports body tube and coarse
adjustment
12. BASE
○ Firm support that bears weight of
microscope
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Exercise 5- The Microscope and Cell
1. Checking the Microscope’s Condition Before Use
Prior to using the microscope, check the condition the microscope from the prior class.
a. Was the microscope placed back in its assigned compartment with the arm
facing out toward you?
b. Was the cord wrapped between the stage and objectives with the plug tucked
inside the cord?
c.
Was the cord relatively untangled?
d. Was the ocular lens clean? (If not, clean the dirty lens with the appropriate lens
cleaner and lens paper (not a paper towel).)
e.
Was the light turned off?
f. Check that the Condenser is at its highest point, directly below the stage.
There is a knob connected to the Condenser that allows it to be moved up and
down.
g. Was the mechanical stage centered so that the stage clips don’t hang over the
edge of the stage?
h. Was the scanning objective lens (4x) (not another objective) placed over the
stage? If not, rotate the nose piece until the scanning objective is facing the stage.
i. Was the stage lowered to the lowest setting possible position? If not, use the
coarse focus knob to do so, not the fine focus knob.
j. Were there any slides remaining on the stage? If so, remove the slide and
notify your instructor. It is important that the slide is placed in the correct box, or it
may get lost.
k.
If any of these conditions were problematic, please let your instructor know.
3. The Lenses of the Compound Microscope
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Exercise 5- The Microscope and Cell
a. The series of lenses in the compound microscope are located in the ocular and in the
objectives. These lenses should be cleaned only if needed. Use only lens paper to clean the
lenses, not paper towels or Kimwipes. If the lens is very dirty, consult your instructor.
b. Lenses for Magnification: The oculars and objectives contribute to the magnification of the
image of a specimen.
The ocular (or eyepiece) magnifies objects ten times their diameter it is said to have a magnifying
power of 10x. (Check your oculars to see where this is inscribed on the ocular edge. Not all
oculars are 10x.)
Note that there are three objectives that are mounted in a nosepiece which revolves so that any
objective can be brought into the functional position in line with the body tube. The magnification
of each objective is also inscribed on the tube of the objective. The magnification is a whole
number, not a decimal number. On the microscopes you are using today the magnification value
follows the letter “E” on the objectives. On other microscopes, the magnification will be indicated
by a number followed by the letter “X” as you saw on the ocular. Varying objectives can be
installed depending on the needs of the laboratory or class, so you need to check the magnification
on your particular microscope. Observe the objectives, and write the ring color around each behind
the name:
· The very short objective is called the scanning objective. The scanning objective
typically has a magnifying power of 4x, depending what has been installed on your
microscope. (color: ___________),
· a medium-length one called the low power objective. The low power objective also has a
magnifying power of 10x (color: ___________),
· and a long one called the high power (also called "high-dry", see reference to “wet”
or oil lens below) objective. The high power objective may have magnifying power of 40x
or more. (color: ___________).
· Depending on the needs of the lab, there may be a fourth objective called the oil
immersion objective. As its name implies, it must be used with a special oil in order to
create the appropriate magnification and not rub against the slide being observed. In general,
we will not use these in general biology, but they are very useful for viewing extremely small
organisms such as bacteria, so they are used in Microbiology courses.
4. How to Use the Compound Microscope
https://www.ncbionetwork.org/educational-resources/videos/use-and-care-microscope
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Exercise 5- The Microscope and Cell
When you are confident you know the functions and names of the parts of the compound microscope
and how to care for it, obtain a commercially prepared slide of the letter "e" for observation. Do
not look through the oculars until the instructions state to do so, or you may end up with a headache.
a.
Plug in the cord and turn up the light intensity.to its maximum value and adjust the iris
diaphragm to its most closed setting. As you proceed you can increase the light passing through
the specimen by gradually opening the iris diaphragm.
b.
Adjust the distance between the oculars: Without placing the prepared slide on the stage
yet, look through the oculars. You are likely going to see two circles of white light. Do not try to
focus your eyes on any one thing, as nothing is in focus yet. Slowly, move the two oculars
together and/or further apart until the two circles of white light become one circle of light. This
circular field of light is the Field of View.
c.
Prepared slide: Hold the prepared slide up to the light and examine it. The first slide for
this exercise has a small piece of paper (with the letter "e") which has been permanently mounted,
using resin or some similar material, between the surfaces of the slide and the coverslip.
With other items, often a stain is used in preparation to allow the observer to clearly see the
specimen if it is transparent. By placing the slide on the white paper next to this text, you will see
color of the stain which will help you locate where the specimen is. Generally, it is in the middle
of the coverslip, but in some preparations, it is off slightly to one side. In this case there is no
stain on the prepared slide, just the circle of paper from which the “e” was cut.
d.
Placing the slide on the stage: Lower the stage using the coarse focus knob, and make
sure the (shortest) scanning objective is facing the stage, so that there is no chance of the slide
scratching any objective lenses. Before looking through the eyepiece (ocular), open the stage clip,
and place the slide on the stage of the microscope beneath the objective, with the label and
coverslip visible on the upper side. The stage clip should be holding the slide in place, not
pressing the slide under it. Place the slide so that you can easily read the words on the label.
They should not be upside down on the lower side or facing away from you. Center the object
below the objective. A specimen should always be viewed first using the scanning objective.
e.
Coarse adjustment with scanning lens: With the scanning lens in place, move the stage
up to its highest point without looking through the oculars. Nothing is in focus yet. No matter
your specimen, always start with coarse adjustment on the scanning first.
Looking through the ocular with your right eye only (squint or cover your left eye), bring the
specimen into focus by turning the coarse focus adjustment knob slowly until the specimen is
generally in focus. Then turning the fine adjustment knob will bring the specimen into sharper
focus.
f.
Focus your left eye: Viewing the specimen with both eyes through both oculars, turn the
left ocular diopter until the specimen is clear in both eyes.
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Exercise 5- The Microscope and Cell
g.
Iris diaphragm: The light coming through the microscope may be either too bright or too
dim. If the amount of light is not satisfactory, it can be adjusted by carefully regulating the size
of the opening of the iris diaphragm by moving the lever beneath the stage. The iris diaphragm
is part of the condenser which concentrates the light coming from the light source.
h.
Adjusting on low and high power objectives - use fine adjustment knobs only: If you
wish to view the specimen using higher magnification, center the specimen in the field, and
carefully rotate the revolving nosepiece to bring the next higher power objective into place
beneath the body tube. The specimen will no longer be in focus. Only research grade, precision
microscopes are parfocal, keeping specimens in focus as the objective lens is changed. Adjust the
focus using only the fine focus adjustment knob when using the low and high power objectives
(Again, the light may have to be adjusted with the iris diaphragm.) Each time you move to the
next higher power objective, be sure you center the specimen beforehand.
i.
Removing slides: When you need remove a slide, be sure to rotate the nose piece to the
scanning objective. Then using the coarse adjustment knob, lower the stage to its lowest position.
Then open the stage clip and remove the slide. Be sure the slide goes back to the correct slide
box. Keep your “e” slide for now, since you still need it.
5. Calculating Total Magnification: The ocular lenses and the lenses in the three objectives have
different powers of magnification. When you view through a microscope, the increase of
magnification is provided by both ocular and objective lenses.
To determine the total magnification of any object viewed with the microscope, multiply the
magnifying power of the ocular by the magnifying power of the objective in use. For example, if the
low power objective is in use, the total magnification of the object would be 10 x 10 or 100 diameters.
(100 diameters means that the image formed by the lenses is 100 times larger than any dimension of
the specimen on the slide.)
Question 1. Calculate the total magnification that would be obtained when using the microscope with
the scanning power objective in place. Show your work, and draw a box around your answer.
Question 2. Calculate the total magnification that would be obtained when using the microscope with
the low power objective in place. Show your work, and draw a box around your answer.
Question 3. Calculate the total magnification that would be obtained when using the microscope with
the high power objective in place. Show your work, and draw box around your answer.
Question 4. Now, write the generalized equation for the calculation of the total magnification. Your
equation should use words, not numbers.
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Exercise 5- The Microscope and Cell
6. You will see a shadowy appearing letter “e.”
Load this web site to do a virtual lab
https://www.ncbionetwork.org/iet/microscope/
1) Go to Explore.
2) Click on the box that has a question mark.
3) Select sample slides
4) Select the Letter E
Question 5. Click on the shadowy e and drag it down toward the bottom of the circle (known as the
Field of View or FOV), which direction does the stage move? Look at the slide mounted on the
microscope while you are doing this.
Question 6. What happens to the stage when you click and drag the e to the top of the FOV?
Question 7. The virtual person who placed this e on the stage, placed it so that the slide label is facing
upward and able to be read. However, how does the e look through the FOV?
Question 8. Slide the Course Focus Adjustment knob to the right until the letter e is clear. Then move
the Fine Focus slider until it is even clearer. What happens to the amount of light?
Question 9. What do you have to do as you move from a lower magnification objective to a higher one?
On a real microscope, would you open or close the iris diaphragm?
Question10. What is the low to high rule? Look for the answers to these in the video: Microscope Basics
https://www.youtube.com/watch?v=ROsc-IrJJ6M
Question 11. Why can you see only part of an image? An alternative way of looking at this is: why does
a dark moon appears on one side? Look for the answers to these in the video: Common Microscope
Mistakes: https://www.youtube.com/watch?v=eZX9U15F5Q8
Question 12. Why can’t I find the same part of the specimen once I move to a higher magnification?
Look for the answers to these in the video: Common Microscope Mistakes:
https://www.youtube.com/watch?v=eZX9U15F5Q8
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Exercise 5- The Microscope and Cell
7. Measuring Microscopic Objects
https://www.youtube.com/watch?v=byhfAARok_0
Frequently, the biologist needs to know the dimensions of the specimen he or she is examining under
the microscope. The following method will enable you to obtain an estimate of the size of an object
by comparing it with Field of View. The Field of View is the diameter of the illuminated circle
observed through the microscope lenses.
To do this it will first be necessary to measure the size of the field. For this measurement, as well as
others you will be making in subsequent laboratory work, the metric system will be used.
Procedure:
1. Place a short, clear plastic ruler over the opening in the center of the stage so that the lines are
visible through the microscope. Place it on top of the stage clips, not under them, or you may
bend the stage clips.
2. Line up one of the vertical lines so that it is just visible at the left side of the circular field of view,
using your low-power (10x) objective.
3. The distance from the center of one line to the center of the next line is 1 millimeter (mm). Count
the number of millimeters included from one side of the field to the opposite side. If the right side
of the field does not coincide with one of the lines, you will have to estimate the portion of a
millimeter. For example, the diagram above shows 1.7 mm.
Question 13. What is the FOV (in millimeters) at low-power of your microscope? Write the units
(mm) after the number. Check your answer with your instructor.
FOVlow = _______ mm
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Exercise 5- The Microscope and Cell
4. For most microscopic measurements we need a much smaller unit than the millimeter. Scientists
use the micrometer (µm), more commonly called the micron, which is one-thousandth of a
millimeter (0.001 mm). (Micro- is symbolized by the Greek letter µ or mu.)
Question 14. How many microns are there in one millimeter? (Hint: which is smaller, micron or
millimeter? Therefore, there would be many __________ in one __________.)
1 mm = ______ µm
Question 15. What is the FOV at low power in microns?
FOVlow = _____ µm
5. Remove the ruler, and return it to the bin on the side lab bench.
6. Turn the high-power objective into place. Note that the field of view is less than 1 mm. Instead of
measuring this field directly, it will be more accurate to obtain the diameter indirectly by the
following calculation. (In order to do this, you must first divide the magnifying power of the low
power objective by the magnifying power of the high power objective, then multiply this by the
diameter of the field under the low-power objective (obtained in Question 13).)
X FOVlow = FOVhigh
Question 16. Calculate the FOV of the high power field in microns (µm). Show your work.
Question 17. Convert the diameter of your field of view you just calculated for high magnification
(answer in the previous question) into millimeters.
Question 18. How did the FOV change when you moved from low power to high power?
Question 19. Is the relationship between magnification and FOV direct or inverse? Explain.
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Exercise 5- The Microscope and Cell
II. Structure and Function
Introduction
Two words you will come across many times in a biology course are structure and function. Our
concern with these words goes beyond a simple dictionary definition According to Webster's New World
Dictionary, function is defined as; "the normal or characteristic action of anything; especially, any of the
natural, specialized actions of an organ or part of an animal or plant." Structure is defined as, "something
composed of interrelated parts forming an organism or organization." A third word we must consider is
complementarity. When we say complementarity of structure and function, we expand the meaning
of the words. Now we mean that the way something is built (structure) complements (adds to or benefits)
its function.
Before we begin, let's talk about a series of relationships found in the world of biology. The phrase ‘levels
of organization’ refers to a series of relationships from small (very, very small) to large (very, very large)
entities. We'll start with the atom. See if you can figure how the terms below are related to each other.
atom
molecules
organelles
cell
tissue
organ
system
organism
population
community
ecosystem
Question 20. Describe how these terms are related:
If you figured that each succeeding term is composed of the elements preceding it, you were correct. As
you might already know, atoms of various types make up molecules. Two atoms of hydrogen and one
atom of oxygen make a molecule of water (H2O). One more example, six atoms of carbon, twelve atoms
of hydrogen, and six atoms oxygen make one molecule of glucose (C6H12O6).
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Exercise 5- The Microscope and Cell
The next step is a big one. Putting together millions of molecules of many types in a particular way, we
have a cell. Cells are special structures. They are the first and smallest forms of life. All living things are
either a single cell or composed of cells. This is the "cell theory," a primary concept of biology. Another
part of the cell theory is that all cells come from pre-existing cells.
Let us move on. If we put together a large group of similar cells, we have tissue. Millions of nerve cells
make up nerve tissue. Millions of smooth muscle cells make up smooth muscle tissue and so on.
The correct combination of different tissue makes an organ. A leaf is an example of a plant organ. It is
composed of epidermal cells, palisade cells, mesophyll cells (spongy layer), and vascular bundles. Other
examples of organs which are composed of tissues are the heart, lungs, and the kidney. (The rest of the
list on the previous page continues on with the type of relationships we have just described. You will be
exposed to many of these relationships during the course.)
A. What is a Cell?
What is a cell really like? By looking at a slide of animal or plant cells do you get an idea of what a cell in
a living organism is like? Hardly! First of all, you can't see the hundreds of things in an ordinary cell
because with an ordinary light microscope they're too small or so thin they're transparent.
Although there are hundreds of thousands of different kinds of cells in the living world, they all work
about the same way. Sure, some have special parts so they are able to perform special functions, but all
cells have basic parts which make them similar.
How many different makes (kinds of motor vehicles) can you think of? How many kinds of chairs or
hammers? We see here the concept of different types of models, but each has basically the same parts
modified for different purposes.
What is it like inside of a cell? Is there a lot of space, is it dark, cold, dry? Well, with very few exceptions
there are no "empty" spaces in cells. For the most part cells are filled with a liquid a little thicker than
milk and not as thick as syrup. Of course, there are exceptions to this also.
You know how a pinball machine lights up and bells ring and scores flash on the screen when the pinball
hits a post. Well, this is similar to a living cell. At any one instant in a living cell there are hundreds of
thousands of complex chemical reactions occurring. If each of these chemical reactions gave off light and
sound like pinball machine, it would probably be like the Fourth of July Light Show at San Diego
Stadium.
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Exercise 5- The Microscope and Cell
B. Microscopic Examination of Cell
Note: Remember, all the cells (tissues) you are observing have three dimensions: length, width,
and depth. Keep in mind that you are initially only seeing two dimensions. The third dimension (depth)
may be appreciated by moving your fine adjustment as you watch the image through your ocular.
1. Animal Cell (Human Cheek Cell)
https://www.youtube.com/watch?v=i2x3MKSJez4
Procedure:
Simple animal cells are easily obtained from your own body. As described below, prepare a wet
mount (a temporary preparation used when the observations are expected to be completed within a
single laboratory period).
a. Slide: Wash and dry a glass slide. Obtain a new toothpick from the front table. Using the flat
end of the toothpick gently scrape the inside of your cheek. You will not see much on the
toothpick but spread what is there onto your slide.
b. Stain: Cover the specimen on the slide with a small drop of methylene blue. (This is a stain
that will make the cells more visible). Next to the stain, add a small drop of tap water from the
dropper bottle provided. Stir the drops together with your toothpick.
c. Coverslip: Carefully cover the preparation with a clean plastic coverslip as follows:
Place one edge of the coverslip near to the drop. The stain and water with which you
mixed the cells will flow along the junction of the edge of the coverslip and the slide. Carefully
lower the coverslip over the specimen keeping the edge of the coverslip in contact with the slide.
In this way, the water will flow slowly and uniformly about the specimen and force out air
bubbles from beneath the coverslip. (A few air bubbles are not a serious problem for your first
slide.)
d. Excess fluid: If liquid spills out from under the coverslip, gently blot the excess with a towel,
so that it will not later drip onto the stage of the microscope.
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Exercise 5- The Microscope and Cell
e. Scan cells: Observe the cells through the microscope, beginning with the scanning lens.
(Review how to use your microscope at the beginning of the lab.) When you look at the cells
they will be separated and spread out over the slide. Recognize that most of the white circles or
ovals on your slide are likely air or water bubbles. Some small groups of cells will stick to one
another in little blue aggregates. Move your slide (using the stage knobs) to where there are
lighter blue areas.
f.
Higher magnification: To see the cells well, move up to low power and then to highdry power. (Don't forget to use only your fine focus knob for low and high power objectives.
Adjust your iris diaphragm to change lighting). Notice the darker-stained oval nucleus in each
cell.
Question 21. Cheek cells have been described as having a modified "fried egg" shape: flat except for
the small lump at the nucleus. Can you tell that the cells are flat? Look for cells overlapping one another.
Also, the edges of some cells may be "folded" back. Draw a few cheek cells, and label the cell
membrane, nucleus and cytoplasm for one of them. (You may need to look these parts up in your
textbook.)
Question 22. Recall the calculation for the FOV at high power. Estimate the size of a single cheek cell
(at its widest point). One way to look at this is to estimate how many of these cells it would take to cross
the entire diameter of the field of light. Then divide the FOV by the number of cells. Assume in the
youtube video that you are seeing the entire FOV.
Width of single cheek cell
=
FOVhigh
.
Number of cells across diameter
= _______________________
2.
= ______ µm
= ______µm
Plant Cell (Onion storage leaf cells)
Procedure:
https://www.youtube.com/watch?v=eD1CdfRycqs
Make a wet mount slide of your onion cells in a fashion similar to the one with the human cheek cell.
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Exercise 5- The Microscope and Cell
a.
Slide: Wash and dry a glass slide and coverslip.
b.
Obtain your peel. Cut a piece of red onion away from the remainder. If the onion is in a
baggy, return the unused portion of onion into the baggy. Bend the onion until you see a layer of
membrane separate from the other parts of the onion. (This is the membrane in between the
layers. It’s thin and transparent.) Place the layer on your slide and use a razor to cut it from the
rest of the onion.
c.
Stain: Optional: If you are using a white onion, add a small drop of methylene blue to
the onion. If are using the purple part of a red onion, then you don’t need the methylene blue, just
add a small drop of water.
e. Coverslip: Carefully, cover the preparation with a clean plastic coverslip as directed above
with the human cheek cell.
f.
Excess fluid: If liquid spills out from under the coverslip, gently blot the excess with a
towel, so that it will not later drip onto the stage of the microscope.
g. Scan cells: Observe the cells through the microscope, beginning with the scanning lens.
(Review how to use your microscope at the beginning of the lab.)
h. Higher magnification: To see the cells well, move up to low power and then to high-dry
power. (Don't forget, you may use the coarse and fine adjustment knobs to focus on scanning
lens, but use only your fine focus knob for low and high power objectives. Adjust your iris
diaphragm to change lighting). Notice the darker-stained oval nucleus in each cell.
Question 23. Onion cells (and plant cells, in general) look a bit more like a brick wall. The cells may
overlapping one another, depending on whether you accidentally folded the membrane peel. Draw a
several onion cells, and label the cell wall, cell membrane, nucleus and cytoplasm for one of them. (You
may need to look these parts up in your textbook.)
Question 24. Why do you think that the onion cell appears blocky, rather than rounded like the animal
cell?
Question 25. Why do you think there is no evidence of chloroplasts in these onion plant cells? (Hint:
Where does an onion with these types of leaves grow: above or below ground? Think about when you
leave an onion on your kitchen counter after a while. What happens?)
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Exercise 5- The Microscope and Cell
Question 26. Recall the calculation for the FOV at high power in a previous question. Estimate the size
of a single onion cell (along its longest edge).
Length of single onion =
FOV
.
= ___________µm
Number of cells across diameter
=
= ___________µm
Additional Cells for Study
Protist Cell (Paramecium)
https://www.youtube.com/watch?v=mh7KOtQTXrw
Paramecium is a single-celled organism commonly found in fresh water environments. Even though
composed of only one cell, paramecium is a highly complex form. One may observe such activities as
ingestion of food, locomotion, excretion of waste, as well as certain interesting structural features such as
the hair-like cilia which cover the surface of the cell.
Question 27. Draw a Paramecium, showing any visible internal structures. Label cell membrane. You
may or may not see evidence of the cilia on the cell membrane. Label where the cilia would be.
Question 28. Can you see movement inside the Paramecium? Does there appear to be a single location
where the yeasts enter the cell? This is called the oral groove. Label this on the drawing you did for the
question above.
Question 29. The Congo Red dye changes from red to blue color when the solution is quite acidic (pH
less than 3). Is there any evidence of color change as the yeast cells are consumed?
Plant Cells: Vascular Tissue
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Exercise 5- The Microscope and Cell
Question 30. Consider what a plant needs to grow and how different substances are moved from one part
of a plant to another. List 3 key factors that a plant needs to grow.
Procedure
Find on the internet.
1. Obtain a slide of Zea mays (corn) stem from the front lab table. (Make sure you have stem and
not root slides!) First, place the slide on a white space in your lab manual. Note the colors and shapes
of the two specimens on the slide.
2. Look at the slide first under scanning power, then under low power. Move the slide around using
the two vertical knobs (mechanical stage control knobs) hanging from the right of the stage. Observe
the two different sections. One section is a group of cells in a circle, and the other is a rectangle,
showing cells running up and down.
1. First look at the cells in the circular section. This is a cross-section (identified on the slide as x.s.
or c.s.) of a young corn stem. Notice the group of three large, round cells that look something like a
face and are stained red. Along with the red cells are smaller cells which are also circular but stained
blue-green in color. This group of cells is a vascular bundle. They function to move substances from
one part of the plant to another.
2. Move your slide so that you are looking at the cells which are running up and down. This is a
longitudinal section (identified on the slide as l.s.). Pay particular attention to the cells which are
stained red. These are the same cells that were circular and stained red in the x.s.
Question 31. Above is a diagram showing the orientation of the cross section and the longitudinal
section as the slices were made from the very young corn plant. Draw a few of the red cells as they
appear in each section. Label the red and green cells as the vascular bundles.
(a) longitudinal section:
(b) cross section:
19
Exercise 5- The Microscope and Cell
Examine the large plant stem model in the laboratory: find the vascular bundles and observe both the
cross section and the longitudinal section shown on the model.
Question 32. Which of these 3 factors you listed in Question 30 are the vascular bundle cells you
observed involved? (If you are not sure, read in your textbook!)
Question 33. Describe what you think is the function of the cell you have drawn above, and explain how
the cell's shape (structure) helps with its function.
Additional Animal Cell: Adipose (fat) tissue cells
Procedure:
https://www.ncbionetwork.org/iet/microscope/
1) Go to Explore.
2) Click on the box that has a question mark.
3) Select Human
4) Adipose Tissue
1. Obtain a slide of adipose tissue from the side lab bench. Start at the scanning power. (Review
how to use your microscope at the beginning of the lab.) At this magnification the tissue you should
be observing will look like a bunch of collapsed circles or a hair net. Scan across the slide to locate
this type of tissue. You will notice that a pinkish stain has been applied to make the cells more
visible. (If you can't see anything but white, remember to adjust your iris diaphragm.)
2. Other types of tissues, often very densely colored, may also be visible in the field. Ignore these
tissues and focus on a small group of adipose cells. Move to low power and then to high-dry power.
You should now be able to see that the thin cell membrane is actually surrounding another inside
membrane with a nucleus (a darkly stained spot) lying between them. Notice the large "empty
space." This is where the lipid triacylglycerol (fat) is stored.
Question 34. Draw one adipose cell. On your drawing, label the nucleus, cell membrane, and the area
where fat is stored.
20
Exercise 5- The Microscope and Cell
Question 35. Remember that adipose cells are spheres and you are only observing two dimensions.
Because the adipose tissue on the slide has been sliced very thin, the cell you drew in Question 34 may
only be a slice across the middle of the whole cell. Imagine a slice from a tomato. Now imagine how
your diagram relates to the entire cell and try to draw the whole cell below.
Question 36. The adipose cell is a beautiful example of structure and function. Its structure is basically a
sphere, which of all possible shapes gives the maximum volume for the amount of surface material used
(cell membrane). Describe how this feature makes the cell well-suited for its function.
Additional Animal Cell: Ciliated Columnar Epithelial Tissue
Procedure:
1. Obtain a slide of pseudo stratified ciliated columnar epithelial tissue from the front lab table.
On this slide will appear a variety of darkly stained cell types. Ciliated cells will be found only where
you see a very regular "edge" to the tissue. Again, start with the scanning lens, center the edge of the
tissue in your field of vision, then move up to low power. (If you don't see anything but white, try
adjusting your iris diaphragm.)
21
Exercise 5- The Microscope and Cell
2. The ciliated cells will be lined up in a row along the edge of the tissue. Cilia will be visible only
on the surfaces of the cells which are facing the open area. Upon close inspection (high-dry power),
the edge of this tissue appears to be covered with very short hairs: each cell has a sort of brush-like
covering. (If you don't see the cilia, dim your light and use your fine focus. If you still don't see the
cilia on the cells, try another area or ask your instructor for help.)
Question 37. Draw one cell with cilia:
Question 38. Epithelial tissues are generally those which cover and protect other tissues. Ciliated
epithelial cells are found on inside surfaces of certain tubes in the body, such as the respiratory airways
and the oviducts. In these locations, ciliated cells are specialized for moving fluids.
a. In the respiratory tract, cilia "beat" in a coordinated manner toward the mouth. Suggest a
valuable result of this behavior.
b. In the oviduct, cilia "beat" in the direction of the uterus. Describe how this behavior could
help reproduction. (Look up the function of the oviduct if this puzzles you.)
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