Block One Lecture 4

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  1. A simple microscope has only __.
    one lens
  2. In a compound microscope the image from the __ is magnified again by the __.
    Total magnification = __
    • objective lens
    • ocular lens
    • objective lens * ocular lens
  3. What is resolution?
    A microscope with a resolving power of __ can distinguish between __. __ of light provide greater resolution.
    the ability of the lenses to distinguish between two points

    0.4 nm

    two points ≥ 0.4 nm.

    Shorter wavelengths
  4. Brightfield Illumination
    Dark objects are visible against a bright background.

    Light reflected off the specimen does not enter the objective lens.
  5. Darkfield Illumination
    Light objects are visible against a dark background.

    Light reflected off the specimen enters the objective lens.
  6. Phase-Contrast Microscopy
    Accentuates diffraction of the light that passes through a specimen.
  7. Differential Interference Contrast Microscopy
    Accentuates diffraction of the light that passes through a specimen; uses two beams of light
  8. Fluorescence Microscopy
    Uses UV light.

    Fluorescent substances absorb UV light and emit visible light.

    Cells may be stained with fluorescent dyes (fluorochromes).
  9. Confocal Microscopy
    Uses fluorochromes and a laser light.

    The laser illuminates each plane in a specimen to produce a 3-D image.
  10. Electron Microscopy
    • Uses electrons instead of light.
    • The shorter wavelength of electrons gives greater resolution.
  11. Transmission Electron Microscopy (TEM)
    Ultrathin sections of specimens.

    Light passes through specimen, then an electromagnetic lens, to a screen or film.

    Specimens may be stained with heavy metal salts.
  12. Transmission Electron Microscopy (TEM)
    10,000-100,000 x; resolution 2.5 nm
  13. Scanning Electron Microscopy (SEM)
    An electron gun produces a beam of electrons that scans the surface of a whole specimen.

    Secondary electrons emitted from the specimen produce the image.
  14. Scanning Electron Microscopy (SEM)
    1000-10,000; resolution 20 nm
  15. Preparation of Specimens for Light Microscopy
    A thin film of a solution of microbes on a slide is a smear.

    A smear is usually fixed to attach the microbes to the slide and to kill the microbes.
  16. Preparing Smears for Staining

    Live or unstained cells have __ with the surrounding medium. However, researchers do make discoveries about __ looking at __.
    • little contrast
    • cell behavior
    • live specimens.
  17. Preparing Smears for Staining

    Stains consist of a __. In a basic dye, the __ is a __.In an acidic dye, the __ is a __.
    Staining the background instead of the cell is called __.
    positive and negative ion

    chromophore is a cation

    the chromophore is an anion

    negative staining
  18. Explain simple stains
    • Use of a single basic dye is called a simple stain.
    • A mordant may be used to hold the stain or coat the specimen to enlarge it.
  19. Explain Gram stains
    • The Gram stain classifies bacteria into gram-positive and gram-negative.
    • Gram-positive bacteria tend to be killed by penicillin and detergents.
    • Gram-negative bacteria are more resistant to antibiotics.
  20. What are the stains used?
    crystal violent = primary stain

    iodine = mordant

    alcohol-acetone = decolorizing agent

    safranin = counterstain
  21. Color of gram positive cells
    • purple
    • purple
    • purple
    • purple
  22. Color of Gram negative cells
    • purple 
    • purple
    • colorless
    • red
  23. What are differential stains: acid-fast stain?
    cells that retain a basic stain in the presence of acid-alcohol are called acid-fast

    non-acid fast cells lose the basic stain when rinsed with acid-alcohol
  24. Special Stains
    • Negative staining is useful for capsules.
    • Heat is required to drive a stain into endospores.
    • Flagella staining requires a mordant to make the flagella wide enough to see
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Block One Lecture 4
Test One
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