Chapter 2 : Microscopy Flashcards
What type of microscope was first invented and is the most widely used today?
Light microscope
What is the resolution limit in a light microscope?
0.2 um ( micrometer)
what is refractive index?
a measure of how much a substance slows the velocity of light
When light passes from one medium to another, what happens to the light?
refracted (bent)
In regards to lenses they focus light rays at a specific place called?
focal point
what kind of microscope would be used to observe stained or unstained specimens to produce a dark image with a bright background and have different magnification?
Bright-field Microscope
what is total magnification?
the product of ocular lenses and objective lenses
The ability of a lens to distinguish objects from each other rather than a single larger object is ?
Resolution
the shorter the wavelength their is less resolution T or F?
F The greater the resolution
what is the distance between the front surface of the lens and the surface of the cover glass or specimen when it is in sharp focus called?
working distance
what three microscopes may be used to gain better contrast between the cells and it structures ?
dark field
phase contrast
differential interference contract
(DIC)
what kind of microscope would produce a bright image against a dark background?
Dark field Microscope
How is the image produced in a Dark field microscope?
light being refracted or reflected by specimen
How is the image produced in a phase contrast microscope ?
produces an image of a darker microbe against a lighter background?
How does DIC microscopes create images ?
detect differences in refractive indices and thickness in different part of specimen
In a fluorescence microscopes how is the image produced?
by exciting a specimen with a wavelength of light that triggers the object to emit fluorescence light
In a fluorescence microscope what do we use to stain the microbe?
fluorochromes - absorb and emit visible fluorescent light
What are fluorochromes?
labeled probes- antibodies or fluorochrome tags
Why do we prepare and stain specimen?
increase visibility
accentuate specifics in morphology
preservation specimen
Scientists want stained cells to resemble living cells as closely as possible, what process is used to preserve the internal and external structures?
Fixation
How does Fixation preserve internal and external structures?
By inactivating enzymes that tell cell morphology to toughen up
There are two type of heat fixation, what are they?
Heat fixation: preserves morphology but destroys subcell structures
Chemical fixation: protects fine sub cell structure and morphology
Ionizable dyes have charged groups, basic dye have negative charge and acidic dyes have positive charges T o F ?
False
basic +
Acidic -
Describe what simple staining is?
- Uses one stain
- used to determine size, shape and bacteria arrangement
Describe what differential staining does ?
divides organisms into groups based on staining
Gram stain and acid fast stain are what kind of staining ?
differential staining
differential staining is used to detect the presence or absence of what structures?
Capsules and flagella
what are the differences between a gram-positive bacteria and a gram-negative bacteria?
gram + have a thicker peptidoglycan layer
gram - have an outer membrane and an inner membrane with a thin peptidoglycan layer
Why is acid-fast staining more useful for staining bacteria members of myobacterium?
due to having a cell wall of lipids, it prevents dye to bind
Capsule staining is used for?
used to visualize polysaccharide capsules around bacteria
How may capsules appear in negative staining ?
colorless against stained background
what is used to provide information about the presence and distribution pattern of flagella?
flagella staining
The electron wavelength is 100,00x shorter than visible light, resulting in a higher resolution image T o F?
True
what occurs in electron microscopy?
electrons replace the light as a beam
how does TEM work?
electrons pass through the specimen to form image
How does SEM work to produce an image?
uses excited electrons from the surface of specimen to make image
What is the purpose for Cryo-electron microscopy?
used to see biomolecules like proteins to see high resolution structures
