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Micro lab midterm Questions and Answers (100%
Correct Answers)
How does smear preparation of cells from a liquid media differ from preparation of
cells from a solid medium?
Ans: you get less bacteria from liquid and you don't need to start with a drop of
water.
Why is it important to limit the quanitity of cells used to prepare a smear?
Ans: if a smear of bacteria is too thick when it is stained it will retain too much of
the stain when the rinse steps are done.
For preparation of a smear on a slide, what is the purpose of heat fixation?
Ans: makes cells stick to the slide when rinsing.
What problems can arise when the slide is heated in a flame?
Ans: the heat can change the shape of the bacteria.
What causes a stain to adhere to bacterial cells?
Ans: the bacteria cell walls make the stain stick during the rinse.
Why are all colored dyes not necessarily useful for simple staining?
Ans: Simple stain does not determine if the bacteria has a thick or thin cell wall...
Which type of microscope produces an image of unstained cells that is most similar
to the one achieved by negative staining?
Ans: Darkfield is similar to negative staining.
A basic dye is utilized to stain bacterial cells.
Ans: simple
A stain that does not penetrate cells is used to color the background.
Ans: negative
Useful for visualizing spirochaetes
Ans: capsule
Heat fixation of the slide is not recommended
Ans: negative
Water is used to remove excess stain from the slide.
Ans: simple
For the simple stain procedure one can use
Ans: methylene blue
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For the negative stain procedure, one can use
Ans: both india ink and nigrosin
Before heat fixation, a wet smear of bacterial cells on a slide must first be
Ans: air dried
Which of the three differential stains would likely be the first used when identifying
an unknown bacterium?
Ans: The gram stain.
What is the function of a mordant?
Ans: is what fixes the stain into the cell wall of the bacteria.
For differential staining, how does a counterstain differ from a primary stain?
Ans: It's a different color from a primary stain.
How do gram-positive and gram-negative bacteria differ in cellular structure?
Ans: Gram- are thin cell walls and are pink (fusia). Gram+ are thick cell walls and are
purple and made of peptiglycan.
Which is the most critical step in the Gram-stain procedure? Why? If this procedure is
done incorrectly, how might that affect the final results?
Ans: The most critical step in the Gram stain is the decolorizer step with acetone
alcohol. If the decolorizer is left on too long Gram positive bacteria will come out
pink and if it is not left on long enough the Gram negatives will come out purple.
How does culture age affect the results of a Gram-stain?
Ans: gram+ will get old and will look pink. The cell wall gets old and thin and stains
pink.
How does culture age affect the results of a spore stain?
Ans: old culture have more spores, bacteria produce more endospores when they are
old.
Why must smear thickness be considered before performing a Gram-stain ?
Ans: If they are too thick gram - will not decolorize properly.
What color are bacterial endospores after a Gram-stain is performed? What does this
tell you about the physical properties of endospores?
Ans: clear inside and around them. They are so thick they will not take up the stain.
What makes Mycobacterium particularly resistant to staining? How are the bacteria in
this genus grouped in terms of Gram classification?
Ans: They have an extra thick cell wall with mycolic acid.
Micro lab midterm Questions and Answers (100%
Correct Answers)
How does smear preparation of cells from a liquid media differ from preparation of
cells from a solid medium?
Ans: you get less bacteria from liquid and you don't need to start with a drop of
water.
Why is it important to limit the quanitity of cells used to prepare a smear?
Ans: if a smear of bacteria is too thick when it is stained it will retain too much of
the stain when the rinse steps are done.
For preparation of a smear on a slide, what is the purpose of heat fixation?
Ans: makes cells stick to the slide when rinsing.
What problems can arise when the slide is heated in a flame?
Ans: the heat can change the shape of the bacteria.
What causes a stain to adhere to bacterial cells?
Ans: the bacteria cell walls make the stain stick during the rinse.
Why are all colored dyes not necessarily useful for simple staining?
Ans: Simple stain does not determine if the bacteria has a thick or thin cell wall...
Which type of microscope produces an image of unstained cells that is most similar
to the one achieved by negative staining?
Ans: Darkfield is similar to negative staining.
A basic dye is utilized to stain bacterial cells.
Ans: simple
A stain that does not penetrate cells is used to color the background.
Ans: negative
Useful for visualizing spirochaetes
Ans: capsule
Heat fixation of the slide is not recommended
Ans: negative
Water is used to remove excess stain from the slide.
Ans: simple
For the simple stain procedure one can use
Ans: methylene blue
, 2 Inquire through: | Professional | Confidential Support
For the negative stain procedure, one can use
Ans: both india ink and nigrosin
Before heat fixation, a wet smear of bacterial cells on a slide must first be
Ans: air dried
Which of the three differential stains would likely be the first used when identifying
an unknown bacterium?
Ans: The gram stain.
What is the function of a mordant?
Ans: is what fixes the stain into the cell wall of the bacteria.
For differential staining, how does a counterstain differ from a primary stain?
Ans: It's a different color from a primary stain.
How do gram-positive and gram-negative bacteria differ in cellular structure?
Ans: Gram- are thin cell walls and are pink (fusia). Gram+ are thick cell walls and are
purple and made of peptiglycan.
Which is the most critical step in the Gram-stain procedure? Why? If this procedure is
done incorrectly, how might that affect the final results?
Ans: The most critical step in the Gram stain is the decolorizer step with acetone
alcohol. If the decolorizer is left on too long Gram positive bacteria will come out
pink and if it is not left on long enough the Gram negatives will come out purple.
How does culture age affect the results of a Gram-stain?
Ans: gram+ will get old and will look pink. The cell wall gets old and thin and stains
pink.
How does culture age affect the results of a spore stain?
Ans: old culture have more spores, bacteria produce more endospores when they are
old.
Why must smear thickness be considered before performing a Gram-stain ?
Ans: If they are too thick gram - will not decolorize properly.
What color are bacterial endospores after a Gram-stain is performed? What does this
tell you about the physical properties of endospores?
Ans: clear inside and around them. They are so thick they will not take up the stain.
What makes Mycobacterium particularly resistant to staining? How are the bacteria in
this genus grouped in terms of Gram classification?
Ans: They have an extra thick cell wall with mycolic acid.
