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Chapter 4 – Microscopes
1
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List the metric units of length in order, from meter to nanometer
 Meter  Decimeter  Centimeter  Millimeter  Micrometer  Nanometer
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(1  1 X 10-1  1 X 10-2  1 X 10-3  1 X 10-6
 1 X 10-9)
3
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 Depending on the wavelengths, different colors are interpreted by the human eye
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4
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5
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 Wavelength of electromagnetic radiation - the shorter the wavelength, the higher the
resolving power
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6
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Discuss the relationship between contrast and staining in microscopy
 Contrast: the difference in intensity between two objects or between an object and its
background
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8
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 A compound microscope uses a series of lenses for magnification
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Compare and contrast bright field, dark field, phase, and fluorescence microscopy
 Bright field microscopy involves an illuminated background as light travels through the
specimen
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 Phase microscopy is used on living organisms that would be altered or damaged by
attaching them to slides or staining them
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o Out of phase when the crests and troughs are not aligned, producing a darker
image
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UV light increases
resolution and contrast
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Compare and contrast electron microscopy with light microscopy
 Electron microscopes have a much greater resolving power (10,000X to 100,000X) compared
to light microscopes, being able to distinguish objects separated by single digits of nm, such
as Ultrastructure
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Contrast transmission electron microscopes with scanning electron microscopes
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Less dense areas fluoresce more
brightly
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Requires a vacuum and dead organisms
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 Scanning Electron Microscopes:
o Image produced: The resulting image is magnified about 10,000X with a resolution
of 20nm
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The primary electrons knock electrons off the surface, and these
scattered secondary electrons pass through a detector and photomultiplier
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o Advantage: Whole specimens can be observed and it produces realistic and 3D
images
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Explain the purposes of a smear, heat fixation, and chemical fixation
 Smear: The thin film of organism that’s fixed to the surface of a microscope slide
 Either heat or chemical fixation kills the microorganism, attaches them firmly to the slide, and
preserves their shape and size
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13
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The colored portion is
called a chromophore
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o Acidic Dyes: Anionic chromophores that stain alkaline structures and work best in
low pH
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14
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After blotting the slide dry, it is observed under a microscope
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 Gram stain: Primary Stain  Mordant (binds to a dye and makes it less soluble)
Decolorizing agent (breaks down thin cell wall of gram negative cells)  Counterstain
 Acid Fast:

o

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Cover the smear with tissue paper
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Remove the tissue paper, cool the slide, and decolorize it with HCl and alcohol
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Counterstain with methylene blue, stains the non-acid-fast cells
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After cooling, the slide is
decolorized with water and counterstained with safranin
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Negative (Capsule) Stain:
o Uses acidic dyes, or negative stains, since they stain the background and leave
negatively charged cells colorless since acidic dyes are negatively charged as well
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15
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o Some scientists define species as: populations of cells that arose from a single cell,
share many properties, differ from other strains, and evolve as a group with at least
70% common DNA
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List the hierarchies of taxa from general to specific
 Kingdom > Phylum > Class > Order > Family > Genus > Species
 Keep Pond Clean Or Froggy Gets Sick
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18
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 Linnaeus didn’t know about viruses, so the original kingdoms were expanded into: Plantae,
Animalia, Fungi, Protista, and Prokaryotae
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19
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 Bacteria- contain bacterial rRNA sequences
 Archaea- contain archaeal rRNA sequences
20
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o Differences in fatty acid composition can differentiate bacteria
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o Agglutination test: antiserum is mixed with a sample of potential target cells
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Phage Typing
o Use of bacteriophages in a petri lawn that infect or destroy specific bacterial cells
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Analysis of Nucleic Acids
o By analyzing the nucleic acid sequence, one can classify and identify certain
microbes
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Those with
similar characteristics have similar GC percentages

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