Unit 7: Review
Microscopy and Cytology Lab
Part I: Microscopy
A. Parts of the compound light microscope
A
Examine the labeled
microscope in your lab
manual. Make sure you
can identify all the parts.
B
C
D
E
F
G
M
H
N
I
J
K
L
Continue
Continue
Part I: Microscopy
B. Principles of microscopy
Magnification – the factor by which a specimen is enlarged. For each specimen
viewed, the total magnification is calculated by multiplying the magnification of the
ocular lens by the magnification of the objective. The light microscope’s ocular
magnification is 10X.
Parfocal and parcentral imaging
Parfocal imaging – the ability of the microscope image to remain in focus when
switching from one objective to the next. Fine adjustment using the fine adjustment
knob might be needed, and the amount of light may need to be adjusted using the
iris diaphragm lever and rheostat.
Parcentral imaging – the image will remain in the center of view when objective
lenses are changed.
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Side view
Front view
Principles of microscopy continued
Field of view
Field of view – the microscope field that appears as a circle
when viewing a slide through the ocular and objective
lenses. As the magnification is increased, the diameter of
the field will decrease. You will need to determine the
width of this circle so that you can make estimates about
the size of an object observed.
1 mm
A ruler is placed across the stage. You are viewing the
image through the scanning objective (4X). The diameter
of the field is 4.2 mm. Convert to µm.
Using the above information you can calculate the field of
view for the low power (10X), high power (40X), and oil
immersion objectives (100X). You should also record area of
your field of view.
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Principles of microscopy continued
Principles of microscopy continued
Depth of focus
Image orientation
Depth of focus – also known as depth of field. It is the vertical distance or thickness
of an object that remains in focus of one time.
Due to the optics involved with the light microscope, the image seen will be real,
inverted, and magnified by the objective. The image is then magnified again by the
ocular lens.
A 3-colored thread slide was focused. Note that one thread is in focus and the
others are not. The clearly focused thread lies on top of the mount.
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40X
400X
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40X
1
Part I: Microscopy
C. Other types of microscopes
Principles of microscopy continued
Resolving power
Resolving power – the degree at which two adjacent points on a specimen are
seen as separate detailed images.
Contrast
Contrast – how well the details of a specimen stand out against a background.
Stains and lighting are used to increase contrast to see detail. See the phase
contrast micrograph in your lab manual.
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Dissecting microscope
The dissecting microscopes are useful when working with larger specimens. The
large distance between the objective and the specimen allows for viewing thicker
mounts and dissections. The illumination is from both above and below. Unlike the
compound microscope, the image you see is not inverted.
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Part II: Cytology
A. Preparing wet mounts
Part II: Cytology
B. Eukaryotic cells
Elodea leaf wet mount
To prepare a wet mount you
need to a clean slide.
A leaf from a sprig of Elodea is
used as the specimen for making
a wet mount.
Add a drop of water onto the
center of a microscope slide.
Then take a thin sample of your
specimen and place it in the
drop of water.
Examine the parts of the cell in this
micrograph.
Cell wall
Central
vacuole
location
Cytoplasm
Cell
membrane
Add a cover slip to your
prepared slide.
Chloroplasts
Continue
Continue
Eukaryotic cells continued
Eukaryotic cells continued
Cell membrane
Onion leaf cell
wet mount
A fleshy leaf from white
onion was
removed. The leaf
was folded back to
remove the thin
layer of epidermis.
A piece of the
epidermis was
placed on a
microscope slide
containing a drop
of iodine.
Examine the parts
of the cell in this
micrograph.
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Cell wall
Cytoplasm
Cell membrane
Location of central vacuole
Nucleolus
Human cheek cells
wet mount
The inside of the
mouth was scraped
with a toothpick. The
scrapings were stirred
in a drop of
methylene blue stain.
Cytoplasm
Nucleus
Examine the parts of
the cell in this
micrograph.
Nucleus
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Part II: Cytology
C. Prokaryotic cells
Prokaryotic cells continued
Bacteria have diverse shapes.
The most common bacterial
shapes include
Bacillus
Gram positive cocci
coccus (cocci, pl.),
bacillus (bacilli, pl.), and
spirillum (spirilla, pl.).
Bacteria are stained with
Gram’s stain. Pink to red color
indicate Gram negative and
purple to blue color indicate
Gram positive.
Gram negative spirilla
(The arrow shows an
aggregate of
about 3 bacilli.)
Continue
Continue
Prokaryotic cells continued
Prokaryotic cells continued
Coccus
Spirillum
(The arrows are pointing
to single cocci. You
also see clusters of
cocci at other
areas.)
(You see clusters of
spirilla in this view.)
Continue
Continue
Part II: Cytology
D. Models
Models continued
C
A
Animal cell model #1
Animal cell/Plant cell Model #2
B
A. Cell membrane
B. Golgi apparatus
C. Mitochondria
D. Cytoplasm
E. Endoplasmic reticulum
F. Nucleus
G. Pair of centrioles
D
E
G
A. Nuclear envelope
B. Nucleolus
C. DNA (chromatin)
D. Nuclear pore
F
A
B
C
D
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Models continued
D
A
Plant cell Model #3
A. Plasma membrane
B. Mitochondria
C. Golgi apparatus
D. Cell wall
E. Endoplasmic reticulum
F. Cytoplasm
G. Central vacuole
H. Chloroplasts
I. Nucleus
B
E
F
G
C
I
H
End of Lab Review☺
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