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24 Cards in this Set
- Front
- Back
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Size range of Eukaryotic cells
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10-100 µm
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Size range of bacteria/archaea (prokaryotic) cells
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0.1-2.0 µm
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size range of viruses
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50-100 mm (0.05 - 0.1 µm)
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magnification
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object appears larger than it is
indicated by (x) occurs as radiation refracts (bends) as it passes through a lens |
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resolution
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ability to distinguish between adjacent objects
2 µm vs 2 nm -- 2 nm is larger resolution: cells at least 2 nm apart will be distinct |
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Light vs. electron microscope
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Sample magnified by:
Light: Glass lens; Electron: magnetic lens Sample illuminated by: Light: Light (visible or UV); Electron: Electrons LOD: Light: ~100-200nm (0.1-0.2 µm); Electron: ~10 nm (=0.1 µm) |
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Bright-field microscope
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Routine work, easy to use, inexpensive
Best resolution: ~0.2µm Bright background; objects dark (exception: negative stain) Requires staining for contrast (cannot view live) |
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Dark-field microscope
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Dark disk in condenser blocks direct light (only light entering objective lens is light reflected by specimen)
Dark background, object bright No staining/fixing required (can view live) |
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Phase contrast microscope
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Amplifies natural contrast between cells vs. background and dense vs. less dense using diffraction plate
No staining or fixation Higher resolution than dark-field |
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Fluorescence Microscope
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uses fluorescence to view object (natural pigment, autofluorescent or fluorescent stains)
Fluorescent objects absorb uv/emit visible bright cells/black background High sensitivity; good for small cells Application: Immunofluorescence assay=determine if specific microbes are present in sample |
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Confocal microscope
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often uses fluorescent dyes or antibodies
a UV laser illuminates specimen ONE PLANE at a time; data is compiled into a 3d image Useful to observe biofilm structure in natural state |
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Electron microscope
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Beam of electrons (vs. visible light) and electromagnets (vs. glass lens)
Operates under vacuum Higher resolution (nm vs. µm) Specimen dried and stained to conduct electricity (no live organisms) Electrons generate micrograph Transmission and Scanning |
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Immunofluorescence assay
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Fluorochrome specific for organism
If fluorochrome binds to organism, it is visible under fluorescent microscope--all other organisms not visible. |
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Chromophores/Stains
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Acidic (-): Nigrosin
Basic (+): Crystal violet, Methylene blue, Malachite green, Safranin |
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Simple stain
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Basic (+) stain
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Negative stain
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acidic stain (bacteria repel stain)
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Differential stain
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gram stain, acid fast, endospore
Cells differ in their ability to be retain first stain during decolorization |
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Gram stain
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Differential stain
Often first test used to identify bacterium (G+): thick cell wall, stained purple (G-): thin cell wall, stained pink |
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Acid Fast Stain
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Differential stain
Acid fast (+): mycolic acid (waxy lipid) associated with cell wall Acid fast (-): no mycolic acid First stain carbolfucshin |
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Notable AF+
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Mycobacterium
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Endospore
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Differential stain
Dormant form of cell that some bacteria produce; extremely resistant Most dyes cannot penetrate endospore Acid stain colors background, basic stain colors cells |
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total magnification
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objective x occular lenses
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Compound
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object magnified twice (2 sets of lenses); (vs. simple)
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Refractive index
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ability to bend light
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