Observing Microbes- Test 1 Flashcards
What is the size of red blood cells?
5 um
What is the size of E.coli bacteria?
1 um
What is the size of T-even bacterio-phages (viruses)?
60 nm
What is the size of DNA double helix?
20 nm
The ability to enlarge objects
magnification
ability to show detail
resolving detail
a measure of how greatly a substance slows the velocity of light
refractive index
What happens to the light when its lower to higher RF?
it is slowed and bent toward normal
What happens to the light when its higher to lower RF?
it is sped up and bent away from normal
the ability to distinguish two adjacent objects; a function of wavelength of light that forms the image along with characteristics of objectives
resolution
What is the symbol for resolving power?
d
What is the symbol for visible light (400-70 nm)?
the upside down y
What is the symbol for the reflective index?
n
What is the symbol for half the angle of the cone of light entering the lens?
delta
the light-bending ability of a medium
refractive lens
The light may bend in air so much that it misses what?
The small high-magnification lens
What is used to keep light from bending?
immersion oil
-most widely used
-specimen is darker than surrounding field
bright-field
-brightly illuminated specimens surrounding by dark field
-live and unstained specimens
dark-field
-transform subtle changes in light waves passing through the specimen into differences in light intensity, best for observing intracellular structures
-accentuates diffraction of the light that passes through a specimen
phase-contrast
-separates the light source into two beams (two refractive indices) giving the appearance of a three-dimensional physical relief
-accentuates diffraction of light that passes through a specimen; uses two beams of light
differential interference contrast
-light objects are visible against a dark background
-light reflected off or refracted through the specimen enters the objective lens
darkfield illumination
-exposes specimen to ultraviolet, violet, or blue light
-fluorescent substances absorb UV light and emit visible light
-cells may be stained with fluorescent dyes (fluorochromes)
Fluorescent microscopy
-uses fluorochromes and a laser light
-the laser illuminates each plane in a specimen to produce a three-dimensional image
Confocal Fluorescence Microscopy
-electrons scatter when they pass through thin sections of a specimen
-transmitted electrons are under vacuum which reduces scatter and are used to produce clear image
-denser regions in specimen scatter more electrons and appear darker
Electron microscopes
preserves internal and external structures and fixes them in position
specimen preparation
-routine use with bacteria and archaea
-preserves overall morphology but not internal structures
heat fixation
-used with larger, more delicate organisms
-protects fine cellular substructure and morphology
chemical fixation
cells that retain a basic stain in the presence of acid-alcohol
acid-fast
-non-acid fast cells lose the basic stain when rinsed with acid-alcohol, and are usually counterstained (with a different color basic stain) to see them
acid fast stain
What are types of special stains and what do they do?
-negative staining- useful for capsules
-endospore staining- heat is required to drive a stain into the endospore
-flagella staining- requires a mordant to make the flagella wide enough to see
