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MGY277 Exam Questions And Verified Answers
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MGY277 Exam Questions AndVerified Answers
limitations of light microscopy - Answer light cannot be used to observe objects near to
or smaller than the wavelength, you'd need to use a light with even smaller wavelength
or electrons
bacteria size - Answer 1-10 micrometers
light microscope - Answer uses visible light
magnify 1000x
easy to observe cell size, shape, and movement
uses lens to bend light directly on it or passed through the sample
electron microscope - Answer magnify 100kx
reveal fine details of cell structure
microscopy principles - Answer magnification, resolution, contrast
refraction
refractive index - Answer a measure of the light-bending ability of a medium
how to improve contrast - Answer change optics
-dark field
stain the sample
-positive/neg staining (+ means cells r darker)
-flurorescent stains
bright field microscope - Answer light passes through specimen, then lenses
evenly lights up entire fov
total magnification of bright field microscope - Answer objective lens
magnification(turny lenses) MULTIPLY by occular lens magnification (eyepieces)
so if using objective 40x and occular is 10x = total magnification 400x
max resolution for light microscope - Answer 0.2 micron...can see shape of bacteria but
not details
,cannot see viruses
what does 100x lens on bright field microscope need - Answer drop of immersion oil
between slide and lens which makes sure theres no air between lens and specimen. oil
has the same refractive index as glass and this prevents light from missing the objective
lens from refraction
this oil isnt used for lower power lenses
what is brightfield bad at - Answer contrast
dark field is better
dark field microscope - Answer directs light towards specimen at an angle instead of
straight up(you can always see dust better if its a dark room and light kind of hits it yk
but not direct)
only the light scattered by specimen enters the objective so cells stand out as bright
against the dark background
*need to use wet mount
electron microscopes - Answer creates electron micrograph
uses electromagnetic lenses, electrons, and a fluorescent screen (to see)
resolution: 0.3nm (1000x better)
drawback of electron microscopes - Answer -expensive
-complicated to operate and high maintancne cost
-lenses and specimen must be in a vacuum bc air molecules interfere w electrons (must
be dead)
stains use toxic/radioactive metals
transmission electron microscope - Answer shoots e thru sample
dark areas=dense
thin sectioning
scanning elecron microscope - Answer observes surface details
surface is coated with film of metal and electron is scanned over it
relatively large specimens can be used
3d effect
steps to staining - Answer 1. FIXATION
, -kills cells to preserve structure (and maybe to get it to accept the stain) or else the cell
would fall apart during staining
-heat is a common fixer
2, PERMEABILIZATION
-disrupts cell membrane to let stain in (not necessary if stain is meant to be outside)
3. MOUNTING
-attach to slide, sometimes cells r just grown directly on the slide to avoid this
4. STANING
-immerse sample in dye solution
5. ADD MORDANT
-chemical that combines with main stain to make it insoluble and less likely to wash
away
6. WASHING
7. COUNTERSTAIN(optionl)
-stain smt else anotehr colour like o the nucleus is pink so everything not nucleus
purple?
dyes - Answer basic: positively charged, attracted to negativley charged cellular
components
-most common used (methylene blue or crystal violet)
acidic dyes: negative charge, cells repel therefore the background is colored (there r
neg things in the cell)
- can be done as wet mount
- doesnt stain cells
- avoid heat-treating it bc the cell shape will distort
simple staining - Answer one dye
differential staining - Answer Gram staining, acid-fast staining
used to distinguish diff bacteria
gram stain method - Answer 1. use the primary stain crystal violet to stain the cell purple
2. use iodine as a mordant
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