MIP 302 Exam 1 Questions with Correct Answers
Why do gram positive cells stain purple, and gram negative cells stain pink? - Answer-gram + cells stain purple because they have a thick peptidoglycan layer that is too thick for the decolorizer to remove the grams iodine, whereas gram - cells have a ...
MIP 302 Exam 1 Questions
with Correct Answers
Why do gram positive cells stain purple, and gram negative cells stain pink? - Answer-
gram + cells stain purple because they have a thick peptidoglycan layer that is too thick
for the decolorizer to remove the grams iodine, whereas gram - cells have a thin ppg
that allow for the removal of the mordant and for them to stain pink
What objective lens do you use to determine the gram stain reaction and the
morphology of bacteria? - Answer-using the 100x objective lens allows for the gram
stain reaction and bacterial morphology to be determined
What is total magnification you use to determine the gram stain and bacteria
morphology? - Answer-10x (ocular lens) x 100x (objective lens) = 1000x total
magnification
What color are gram +/- cells if you forget to add grams iodine? - Answer-both gram +
and gram - will stain pink
What color are gram +/- cells if you forget to add safranin. - Answer-gram + will be
purple, gram - will be colorless
What color are gram +/- cells if you forget to add crystal violet - Answer-both gram + &
gram - are pink
What color do gram +/- cells stain if you forget to add decolorizer? - Answer-both gram
+ & gram - will stain purple
Describe the function of heating the smear after application of the primary stain in the
acid fast stain procedure - Answer-Heating drives the primary stain (carbon fuchsin)
past the thick, waxy layer of mycolic acid and into the cell
Why do acid-fast + cells stain pink, & acid-fast - cells stain blue - Answer-Acid-fast +
cells stain hot pink because carol fuchsin is driven past the mycolic acid and into the cell
by using heat. The carbon fuchsin is then "trapped" in the cell by the mycolic acid and
therefore the pink color from the carbon fuchsin in not removed by the decolorizer.
However, acid-fast - cells do not have mycolic acid and the carbon fuchsin is removed
during the decolorizing process.
, Imagine that you were to preform an endospore stain on a bacterium growing on a TSA
slant. The bacterium is known to produce spores, but you do not visualize any in your
smear. Explain why this is so. - Answer-Spores are not visible because they were not
grown in the proper medium. In the slant, the bacteria had all the nutrients they needed
and therefore did not begin producing spores. If they had been grown in endospore
agar, the spores would have been visible
Describe the function of heating the smear after the application of the primary stain in
the endospore stain procedure - Answer-Heat is used after the primary stain (malachite
green) is applied in order to drive the stain past the endospores thick cell wall.
If you preform an endospore stain and everything appears green, what could have gone
wrong? - Answer-The cells were underdecolorized
Why do spores appear as clear holes within a cell when a gram stain is preformed? -
Answer-Because there is no heat applied in the gram stain process, therefore the stain
cannot penetrate the thick cell wall of the endospore and they appear clear
Would you be able to visualize free endospores using the gram stain? - Answer-No,
because since there is no heat step in the gram stain process, the stain would be
unable to penetrate the endospore thick cell wall therefore they would appear clear and
not be visible on the bright microscope background
How can you differentiate bacterial cocci from bacterial endospores using the
endospore stain? - Answer-The bacterial endospores would appear green, whereas the
bacterial cocci would appear pink.
What should you do if you get a skin cut in the lab? - Answer-Report to instructor
what should you do if you drop a test tube that contains bacterial cultures and it shatters
on the floor? - Answer-report to instructor & dispose of waste in the manner prescribed
by instructor
when should you mouth pipette? - Answer-never
list 3 items that should be discarded in the red incinerator bin - Answer-plastic tubes,
glass slides, swabs, gloves
when should you decontaminate your bench with disinfectant - Answer-when you enter
and complete lab
when is it okay to eat/drink in lab - Answer-never
what is "proper lab attire" - Answer-lab coat, close-toed shoes, safety goggles, long hair
pulled back
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