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Size of a eukaryotic cells
10 - 500 micrometer
Size of prokaryotic cells
1 - 10 micrometer
Size of a virus
20nm - 1000nm(1mincrometer)
ability of the lenses to distinguish between two points
Describe resolution of a light microscope
ex. virus 20 nm and microscopes's resolving power is 25nm the microscope will not be able to see it.
is the light - banding ability of a medium
Why is there such a thing as an "oil immersion" lens on lirght micros.?
Ther shorter waveleneghts of light provied greater resolution. Immersion oil is used to keep light from bending.
dark objects are visible againsgt a bright backround. Light reflected off the specimen does not enter the objective lens.
- uses electron insted of light
- shorter wavelength of electrons gives greater resolution.
have postivie and negative ions
- color due to cation (+)
- cristal violet, safranin... stain the bacteria
- color due to anion (-)
- stain the background not the bacteria
How is a specimen prepaired?
microbes are smeared an a slide - air dry - fix by flaiming killing microbes, than stain.
use of a single basic dye - stains the entire microorganism to show bgasic shape and structure.
What is a mordant?
may be used to intensify the stain, increase the affinity of the stain for the specimen, or to coat the specimen to enlarge it. ex. iodine.
these stians react differently with different kinds of bacteria, and allow us t otell the difference bwtween them.
The Gram stain
- Gram - positive
- Gram - negative
1st step making a Gram stain after the bacterial smear is made and heat fixed.
- Smea is flooed with crystal violet for 60 sec. than rinsed with distilled water
- ~crystal violet sticks to peptidoglycan in the cell wall
- it is a primary stain -colors all the cell and all will look purple G+ and G-
2nd Step making a Gram stain
- flood with iodine for 60 second than rinse with distilled water
- ~iodine is a mordant will increase the affinity of the cyrstal violet
3rd step making gram stain ( the differential step)
- flood with an acetone/ethanol wash (decolar agent) for 5 seconds than rinse w/distilled water.
- in Gram + cells look purple
- Gram - look clear the ethanol washes CV-I of peptidoglycan layers.
4th step making Gram stain
flood with safranin stain for 1.5-2 min, then rinsed with distilled water
- is pink in color and stain all bacteria
- G + will not change the color and still look purple
- G - was clear and will be stained pink.
Grap positive bacteria
- they have a thick peptidogllycan layer in their cell wall (disaccharides and amino acids) which is the part that stains purpel due to crystal violet and iodine wash.
- Killed easily by penecilin
Gran negative bacteria
- Thin layer of peptidoglycan
- Contain a layer of lipopolysaccharide (endotoxin) as part of their cell wall - more resistant to antibiotics which cannot penetrate this lipo layer.
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