BIOS 260 lab final SCC-Test Questions and Answers
What are the differences between prokaryotic and eukaryotic cells and can you distinguish
them from a observing them on a slide? Correct Ans-Prokaryotic cell: 1-5um, mo
membrane bound organelles, 70s ribosomes, rotar flagellar movement, single circular
chromosome.
Eukaryotic: 10-100um, have membrane bound organelles, 80s ribosome, whiplike flagellar
movement, linear DNA.
Define Protozoans Correct Ans-Unicellular, heterotrophic, Asexual and sexual
characteristics, The trophozoite is the vegetative (feeding) stage and the cyst is the resting
stage of protozoans. Both unicellular and Eukaryotic.
Give an example of a basic dye? Correct Ans-Crystal violet
Give an example of a acidic dye? Correct Ans-Nigrosen (negative stain)
What is the purpose of heat fixing a smear? Correct Ans-Heat fixing kills the bacteria,
makes them adhere to the slide, and congulates cytoplasmic protein to make them more
visible, also distorts the cells to some extent.
, BIOS 260 lab final SCC-Test Questions and Answers
What are the advantages of using a negative stain? Correct Ans-Used to determine
morphology and cellular arrangements in bacteria that are too delicate to withstand heat
fixing. Also used to determine the accurate size since there is minimal cell shrinkage.
Which dye is used in the negative stain and is it a basic or acidic dye? Correct Ans-Use
Nigrosen and it is acidic.
Why is the background stained in a negative stain? Correct Ans-Bacteria are negatively
charged, and since the acidic stain Nigrosin is also negatively charged, the bacteria repels the
negatively charged stain, so the cell remains unstained against a colored background.
What is the charge of the surface of bacteria? Correct Ans-Negatively charged.
Is the gram stain a differential or simple stain? Correct Ans-Differential stain in which a
decolorization step occurs between the application of two basic stains.
Is a good emulsion on the slide chunky, invisible, or a faint haze? Correct Ans-Good
emulsion is about size of a dime and dries to a faint haze on slide.
, BIOS 260 lab final SCC-Test Questions and Answers
What is the names of the primary stain, the mordant, the decolorizer, and the counterstain of
a gram stain? Correct Ans-Primary stain: crystal violet
Mordant: grams iodine
Decolorizer: 95% alcohol (same as 95% ethanol)
Counterstain: safranin.
What are several reasons a gram stain may not work? Correct Ans-Over-decolorization
Under decolorize
Inconsistency of preparation of emulsion.
Some gram positives lose their ability to retain the crystal violet-iodine complex in as little as
24 hours of incubation.
Give an example of a gram positive rod? Correct Ans-Bacillus subtilis
Give an example of a gram positive coccus? Correct Ans-Staphylococcus epidermidis
Give an example of a gram negative rod? Correct Ans-Escherichia coli
, BIOS 260 lab final SCC-Test Questions and Answers
How is the motility test medium inoculated? Correct Ans-Using a straight inoculating
needle, inoculate two tubes with the test organisms. (try to avoid lateral movement when
performing this stab). Incinerate the inoculating needle after each stab.
How do you detect motility? Correct Ans-Motile: red diffuse growth radiating outward
from the stab line.
Non-motile: red growth only along the stab line.
What does a simple stain look like? Correct Ans-
What does motile and non motile look like? Correct Ans-
Describe the composition of agar in a motility test medium? Correct Ans-Semisolid
medium designed to detect bacterial motility. Agar concentration is reduced from the typical
1.5% to 0.4% - just enough to maintain form while allowing movement of motile bacteria.
Contains tetrazolium salt (TTC)
What are the differences between prokaryotic and eukaryotic cells and can you distinguish
them from a observing them on a slide? Correct Ans-Prokaryotic cell: 1-5um, mo
membrane bound organelles, 70s ribosomes, rotar flagellar movement, single circular
chromosome.
Eukaryotic: 10-100um, have membrane bound organelles, 80s ribosome, whiplike flagellar
movement, linear DNA.
Define Protozoans Correct Ans-Unicellular, heterotrophic, Asexual and sexual
characteristics, The trophozoite is the vegetative (feeding) stage and the cyst is the resting
stage of protozoans. Both unicellular and Eukaryotic.
Give an example of a basic dye? Correct Ans-Crystal violet
Give an example of a acidic dye? Correct Ans-Nigrosen (negative stain)
What is the purpose of heat fixing a smear? Correct Ans-Heat fixing kills the bacteria,
makes them adhere to the slide, and congulates cytoplasmic protein to make them more
visible, also distorts the cells to some extent.
, BIOS 260 lab final SCC-Test Questions and Answers
What are the advantages of using a negative stain? Correct Ans-Used to determine
morphology and cellular arrangements in bacteria that are too delicate to withstand heat
fixing. Also used to determine the accurate size since there is minimal cell shrinkage.
Which dye is used in the negative stain and is it a basic or acidic dye? Correct Ans-Use
Nigrosen and it is acidic.
Why is the background stained in a negative stain? Correct Ans-Bacteria are negatively
charged, and since the acidic stain Nigrosin is also negatively charged, the bacteria repels the
negatively charged stain, so the cell remains unstained against a colored background.
What is the charge of the surface of bacteria? Correct Ans-Negatively charged.
Is the gram stain a differential or simple stain? Correct Ans-Differential stain in which a
decolorization step occurs between the application of two basic stains.
Is a good emulsion on the slide chunky, invisible, or a faint haze? Correct Ans-Good
emulsion is about size of a dime and dries to a faint haze on slide.
, BIOS 260 lab final SCC-Test Questions and Answers
What is the names of the primary stain, the mordant, the decolorizer, and the counterstain of
a gram stain? Correct Ans-Primary stain: crystal violet
Mordant: grams iodine
Decolorizer: 95% alcohol (same as 95% ethanol)
Counterstain: safranin.
What are several reasons a gram stain may not work? Correct Ans-Over-decolorization
Under decolorize
Inconsistency of preparation of emulsion.
Some gram positives lose their ability to retain the crystal violet-iodine complex in as little as
24 hours of incubation.
Give an example of a gram positive rod? Correct Ans-Bacillus subtilis
Give an example of a gram positive coccus? Correct Ans-Staphylococcus epidermidis
Give an example of a gram negative rod? Correct Ans-Escherichia coli
, BIOS 260 lab final SCC-Test Questions and Answers
How is the motility test medium inoculated? Correct Ans-Using a straight inoculating
needle, inoculate two tubes with the test organisms. (try to avoid lateral movement when
performing this stab). Incinerate the inoculating needle after each stab.
How do you detect motility? Correct Ans-Motile: red diffuse growth radiating outward
from the stab line.
Non-motile: red growth only along the stab line.
What does a simple stain look like? Correct Ans-
What does motile and non motile look like? Correct Ans-
Describe the composition of agar in a motility test medium? Correct Ans-Semisolid
medium designed to detect bacterial motility. Agar concentration is reduced from the typical
1.5% to 0.4% - just enough to maintain form while allowing movement of motile bacteria.
Contains tetrazolium salt (TTC)
