Download Cell Lab Extra

Standard Biology
Name: ______________________________
Period: _____
CELL LAB
Objective: To become more comfortable with the proper operation of the microscope while observing
and drawing different types of eukaryotic cells (prokaryotes are really, really tiny, so we won't be
observing them). You will observe various prepared slides in addition to staining and mounting two
types of cells: onion cells and your cheek cells.
Background Information: Sometimes distinguishing one cell from another requires the use of dyes or
stains that highlight various structural features of the organism. Many stains color particular types of
cells, while leaving others alone. The Gram stain (actually a series of staining and washing techniques)
colors different types of bacteria based on the type of cell wall they possess and therefore is often used
to help classify bacteria. Other types of stains color particular parts of cells. For example, methylene
blue binds to DNA, so when we stain a cell with methylene blue, it allows us to see the nucleus of that
cell. Iodine binds to polysaccharides, so staining a plant cell with iodine allows us to see the cell wall,
chloroplasts and amyloplasts (starch storage vacuoles present in certain types of plant cells).
Materials:
Microscope
2 Microscope slides
2 Cover slips
Beaker
Dropper of Methylene Blue Stain
Paper Towel
Kimwipes
Toothpick
2 Prepared Slides (Diatoms, Protists, or Algae)
Piece of onion
Dropper of Iodine solution
Procedure:
Part I: Prepared Slides
1. Set up microscope.
2. Look at your first prepared slide under the microscope. Start
with the scanning objective lens and work your way up to the
high power objective.
3. Pick out a nice, beautiful cell and draw it in the “Illustration
1” circle to the right using either the low or high power; you
decide which looks best. Be sure to label your drawing
(name of slide that you are looking at) and include
magnification.
4. Repeat steps 2 & 3 with your other prepared slide, using the Illustration 1: ______________
“Illustration 2” circle below for your drawing.
Magnification:___________
Illustration 2: ______________
Magnification:___________
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Part II: Cheek Cells
1. You will prepare a wet mount of your own cheek cells.
2. Using the blunt end of a toothpick, gently scrape the inside
of your cheek (you do not need to gouge until you bleed).
3. Smear the sample onto one of your slides and wait until it
dries (you can gently blow on it to speed up the process).
4. Add one drop of the methylene blue stain and let it sit for
60 seconds.
5. Use the edge of a paper towel to soak up the excess stain.
6. Add one drop of water and cover with a cover slip.
7. First view it on scanning power and work your way up to
high power.
8. Draw and label the cytoplasm, cell membrane and nucleus
under high power in the “Illustration 3” circle to the right.
Illustration 3: ______________
Magnification:___________
Part III: Onion Cells
1. Prepare a wet mount of onion cells on a clean glass slide.
2. To do this, peel thin, transparent single layers of inner
epidermis of an onion using your fingernails. Some practice
is needed to obtain very thin samples of tissue. One trick is
to “dig into” the onion a bit with your fingernails, then pull
sideways and upward until you find a cellophane-like piece
of tissue beginning to come off with the small “hunk” of
onion.
3. Transfer only the transparent epidermis sample to a glass
slide (remove any hunks of onion).
Illustration 4: ______________
4. Add a drop or two of iodine solution and a cover slip.
5. First view it on scanning power and work your way up to
Magnification:___________
high power.
6. Draw and label the cytoplasm, cell membrane and any other organelles that you might be able
to see under high power in the “Illustration 4” circle to the right.
7. Put the iodine stained onion cells slide to the side (do not rinse them off!).
8. Repeat steps 2 through 5 but use methylene blue instead of
iodine as the stain.
9. Draw and label the cytoplasm, cell membrane, nucleus and
any other organelles that you might be able to see under
high power in the “Illustration 5” to the left.
10. Observe what structures are stained in the onion cells. How
do the staining effects compare with those of iodine that
you used previously?
Illustration 5: ______________
Magnification:___________
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Analysis
1. Were the cheek and onion cells you viewed prokaryotes or eukaryotes? How can you tell?
2. What structures does methylene blue stain? What structures does iodine stain?
3. What are the three ways in which plant cells differ from animal cells?
Extra Credit:
4. The following table lists the diameter of the field of view at each magnification.
Objective Lens (Total Magnification)
Diameter of Field of View (millimeters)
Scanning (40x)
4.5
Low Power (100x)
1.8
High Power (400x)
0.45 (= 450 micrometers)
Using these scales, what is the approximate size of your cheek cell? Your onion cell?
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