CP BIO: Microscopes
Use light or electrons to
magnify
Enable us to see the shape
and structure of very
small objects
Magnification
Total magnification = ocular lens X objective lens
Real size
Magnified 400 X
Cell walls
Elodea canadensis
Pond weed
chloroplasts
cytoplasm
central vacuole
How two lenses magnifies
Resolution or Resolving Power
Resolution = sharpness, clarity of focused image
• “Ability to show two close points as separate”
• Depends on shape and perfection of lenses
• A light microscope can show objects as small as 1 m
high resolution lens
lower resolution lens
Depth of Field
• Thickness of layer in focus
• Higher magnification  thinner layer
Light Microscopes (LM)
• Light passes through a thin specimen
• Use lenses to focus light
– Simple microscope – one lens
– Compound microscope – two lenses
• Magnifies image twice
Leeuwenhoek’s Microscope
• Anton von Leeuwenhoek, 1600s
• First powerful scope with high resolution
– Single lens
– Magnify ~ 300 X
Leeuwenhoek’s microscope
Advantages of light microscopes
- Can magnify up to 2000 times
- Shows shape and structure of cells and
tiny organisms
- Specimens can be alive
Disadvantages
- Specimens must be thin enough for light to
pass through
- Image appears inverted and backwards
- Often need stain to see better (stain kills cells)
Cheek cells with stain
Common stains: methylene blue, Lugol’s iodine
“Vital stains” - stain without killing cells
Phase-Contrast Microscope
Increases contrast without staining
good for living organisms
Cheek cells without stain
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Compound Microscope
cheek cells – stained
nucleus
cytoplasm
cell membrane
Phase-Contrast
cheek cells –unstained
nucleus
cytoplasm
cell membrane
Amoeba, one-celled organism
preserved, stained
Compound scope
alive, moving
Phase-Contrast scope
Cell cycle, under phase contrast
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Stereomicroscopy
“Dissecting microscope”
Has ocular lens and
objective lens for
each eye 
stereoscopic vision,
3-D
Image NOT inverted
Magnifies 10-50X
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Advantages of stereoscopes
• Image NOT inverted or backwards
• Makes manipulation easy
• Specimens can be solid, living
• Disadvantage: magnifies up to ~50 X
Stereomicroscope – whole specimens
chick embryo
soil worm
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Electron
Microscope
Uses electrons
instead of light
Magnets focus the
electron beam
Image on monitor
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Electron Microscope
• Invented 1930s
• Very high magnification and
resolution
• Show cell details – internal
anatomy, “ultrastructure”
Advantages
of electron microscopy
• Electron are much smaller than the
wavelength of light – show things that light
cannot show
• Very high magnification – up to 500,000X
• Very high resolution - up to 1 nanometer
• DISADVANTAGE – specimen must be
dead, dried, coated, in vacuum chamber
Scanning Electron Microscope
SEM
• Electron beam skims across specimen
surface
• Shows tiny surface details
• Magnifies up to 50,000 times
• DISADVANTAGE: shows surface, but not
interior
Compare LM and SEM
Blood cells (LM)
Blood cells (SEM)
SEM micrographs
Euglena (protist)
SEM
Ant head, SEM
Scanning Electron Microscope (SEM)
shows surface details
Electrons scan across surface of specimen
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SEM of DNA
Image made with special scanning “tunneling” microscope
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Transmission Electron Microscope
(TEM) shows inside cells
• Electrons pass through thin specimen
• Shows great detail of internal structure
• Magnifies up to 500,000 times!!
Rough ER
Mitochondria
Nucleus
Comparing microscopes
Euglena SEM
Euglena LM
Euglena TEM
Transmission Electron Microscope
Bacterium dividing
Muscle fibers
Phage virus
Liver cells
Cilia and basal bodies
Chloroplast
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Comparing microscopes
Euglena, LM
Euglena, SEM
Euglena, TEM
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Which type of microscope
produced these micrographs?
Amoeba, preserved and stained
Vacuole inside a cell
Amoeba, alive and unstained
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Which type of microscope made
these micrographs?
Female and male fruit fly
Closterium Unicellular green alga
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Name the microscope
Leaf cross-section 400X
chloroplast 5,000 X
Name the microscope
Iridescent beetle
Eye of a housefly
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Which microscope?
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Fluorescent Microscopy
• Uses lasers on thin slices; confocal scope
• Fluorescent dyes show different molecules
Cancer cells tagged with 3 fluorescent dyes shows cell microtubules
(blue), microfilaments (yellow), DNA (green)
Confocal Microscopy
E. Coli bacteria
Specialized Cells in the Ear