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BIO 235 Microbiology Exam 1 Questions and Answers Graded A (1) (1).docx
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BIO 235 Microbiology Exam 1 Questionsand Answers Graded A
units of measurement - 1 µm = 10-6 m = 10-3 mm
1 nm = 10-9 m = 10-6 mm
1000 nm = 1 µm
0.001 µm = 1 nm
total magnification (compound microscopes) - -the image from the objective lens is
magnified again by the ocular lens
-total magnification = objective lens x ocular
lens
resolution - -the ability of the lenses to distinguish two points.
-shorter wavelengths of light provide greater resolution
objective lens - lens closest to the specimen
condenser - focuses light onto the specimen
brightfield illumination microscopy - -dark objects are visible against a bright
background
-light reflected off the specimen does not enter
the objective lens
-used for stained microbial cells
darkfield illumination microscopy - -light objects are visible against a dark
background
-light reflected off the specimen enters the objective lens
-used for cells that do not stain easily
phase contrast microscopy - -accentuates the diffraction of a light that passes
through a specimen
, -to facilitate detailed examination of the internal structures of living specimens
DI contrast microscopy - -differential interference
-uses a polarizer to create two distinct beams of polarized light
-typically used on unstained
cells to reveal internal structures
-gives structures such as nucleus, endospores, vacuoles, and granules a three-
dimensional
appearance
fluorescence microscopy - -used to visualize specimens that fluoresce, emitting
light of one color after absorbing light of different color
-some cells naturally fluoresce due to components like chlorophyll, but others have
to be stained with a fluorescent dye
-often rapidly used to detect and identify microbes in tissues or clinical specimens
as well as for enumerating bacteria in a natural environment
confocal scanning laser microscopy - -uses a computerized microscope coupled
with a laser source to generate a 3D image
-computer can focus the laser on single layers of the specimen
-different layers can then be compiled for a 3D image
TEM - -transmission electron microscopy
-uses ultra-thin sections of specimens
-light passes through specimen, then an electromagnetic lens, to a screen or film
-enables visualization of structures at the molecular level
-specimen must be very thin (20-60nm) and be stained with heavy-metal salts
-resolution 0.2nm
SEM - -scanning election microscopy
-specimen is coated with a thing film of heavy metal (like gold)
-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
-only the surface of an object is visualized
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