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Test bank for microbiology, a systems approach, 6th edition, marjorie kelly cowan, heidi smith.
Test bank for microbiology, a systems approach, 6th edition, marjorie kelly cowan, heidi smith.
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Microbiology-A Systems Approach by Marjorie Kely Cowan & Heidi SmChapter
1. Gram Negative Bacteria: Gram Negative Bacteria have a very thin
peptidoglycan layer, so CV iodine is easily washed away ( decolorized by ethanol
wash). Therefore gram negative bacteria is counter stained by Safranin and appea
red.
2. Real Image: Light is concentrated by the condenser through the specimen an
then through the objective lens where it is them refracted and the image is them
enlarged.
3. Levels of magnification?: Final magnification is calculated by multiplying
power of the objective by power of the ocular. (Ocular is always 10)
4. What is magnification?: The increase in size of a visible object
5. What is Resolution?: Resolution is the ability to distinguish between two
separate objects. Shorter wavelengths produce higher resolution.
6. What is immersion oil used for?: Immersion oil is a technique used to
increase the resolution of a microscope.
7. What is contrast used for?: Contrast is a sample (light vs. dark)is achieved b
altering the refractive index. Easiest way to contrast is by staining.
8. What is Wet Mount?: Wet Mount is used to observe microorganisms in their
natural state.
9. Heat Fixation: A loopful of cells are smeared onto the surface of a slide and
allowed to air dry. The slide is briefly passed over the flame to fix the cells to th
slide by denaturing the lipids and proteins which acts like glue. Specimen must
be dry before heat fixation to prevent the cells from boiling.
10. What are positive stains?: Positive stains are positively charges dyes which
adhere directly to negatively charged cell surfaces.
11. How many types of stains?: Positive and negative stains
12. What are negative stains?: Acidic dyes are negatively charged. They stain th
background of the slide and leave the specimen unstained. Smear is not heat
fixed prior to negative staining.
13. What is a simple stain?: A simple stain is where only one type of dye is used.
It is used to see basic morphology, size and arrangement of cells.
14. What is a differential stain?: More than one dye is used to contrast different
types of cells or cell structures.
Gram stain (most important)
Spore stain
Acid-Fast Stain
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