BIO SCI M118L MICROBIO LAB QUIZ 1 Questions and Answers
Question 1.
selective media
Correct Answer: inhibits growth of a group of organisms
Question 2.
complex media
Correct Answer: contains one or more ingredients of unknown composition
Question 3.
purpose of streaking
Correct Answer: to dilute original sample to obtain single colonies
Question 4.
catalase test methods and results
Correct Answer: Methods: expose bacteria to hydrogen peroxide Results:
breakdown of hydrogen peroxide produces oxygen gas => if it bubbles, there is
catalase
Question 5.
sources of error in a gram stain
Correct Answer: - too many cells -> clumps -> trap crystal violet dye during
wash -> false positive - old cultures -> gram positive can stain false gram
negative or variable - heat fixing for too long -> gram positive will stain gram
negative (heat disrupts cell wall) - over or under destaining -> affects how much
crystal violet remains in the cells
Question 6.
phenol red test methods and results
Correct Answer: Methods: - Add cells to phenol red broth - Seal using amojel ->
creates anaerobic environment Results: - Yellow: glucose is fermented and acid
is produced - Pushed up plug/bubble: gas was produced ***Remember to keep a
control without carbon source (e.g. glucose) -> should remain red
Question 7.
Why do we use King's agar B and not S1 for the Fluorescent Pigment Test?
Correct Answer: Pigment production on both the S1 plate and the King's agar B
plate will produce a yellow-green color. S1 media, however, contains a
detergent that interferes with the cell membrane of gram positive bacteria,
preventing their growth, and an antibiotic that kills facultative anaerobic gram
negative bacteria. King's agar B is not selective and, therefore, can be used on
more types of bacteria. King's agar B contains phosphorus and magnesium
which is known to increase production of the fluorescent pigment. King's agar B
lacks compounds that inhibit the growth of certain types of organisms
Question 8.
endospore test
Correct Answer: determines whether organism can form spores
, Question 9.
Is the control used in the phenol red test is a positive or negative control? Does it use
media with glucose or without glucose? Is an organism or no organism inoculated?
Correct Answer: negative, without glucose, organism
Question 10.
How does a gram stain work?
Correct Answer: - crystal violet dye stains both gram positive and gram negative
cells - iodine forms a complex with crystal violet, increasing the size of the dye -
destainer (acetone/ethanol solution) washes out crystal violet while shrinking
pores of peptidoglycan cell wall and permeabilizes lipid outer membrane of
gram negative cells -> traps crystal violet in gram positive cells -> it remains
purple while the gram positive cells are colorless - Safranin-O stains both gram
positive and negative cells, but is u detectable underneath the purple in gram
positive cells -> gram positive is purple, gram negative is pink
Question 11.
Name the two classes of microorganisms (classification based on oxygen consumption)
that utilize oxygen to produce chemical energy (ATP) through the electron transport chain.
Correct Answer: strict aerobes and facultative anaerobes
Question 12.
peptones
Correct Answer: unknown components; nutrient rich extracts from milk, yeast,
beef, etc.
Question 13.
purpose of ABA DABA process
Correct Answer: initial identification of the organism; either gives you the family
or genus of the bacterium
Question 14.
example of differential media
Correct Answer: MacConkey agar: contains pH indicator neutral red - organisms
that ferment lactose (sugar in the media) produce an acid end product -> lowers
pH -> turns red - organisms that do not ferment lactose remain colorless
Question 15.
differential media
Correct Answer: allows one to distinguish between different types of bacteria
growing on a single plate - colored dyes taken up by specific organisms - pH
indicators that alter the color of media surrounding a colony depending on the
secretion
Question 16.
dye in oxidase paper
Correct Answer: N,N-dimethyl phenylenediamine
Question 1.
selective media
Correct Answer: inhibits growth of a group of organisms
Question 2.
complex media
Correct Answer: contains one or more ingredients of unknown composition
Question 3.
purpose of streaking
Correct Answer: to dilute original sample to obtain single colonies
Question 4.
catalase test methods and results
Correct Answer: Methods: expose bacteria to hydrogen peroxide Results:
breakdown of hydrogen peroxide produces oxygen gas => if it bubbles, there is
catalase
Question 5.
sources of error in a gram stain
Correct Answer: - too many cells -> clumps -> trap crystal violet dye during
wash -> false positive - old cultures -> gram positive can stain false gram
negative or variable - heat fixing for too long -> gram positive will stain gram
negative (heat disrupts cell wall) - over or under destaining -> affects how much
crystal violet remains in the cells
Question 6.
phenol red test methods and results
Correct Answer: Methods: - Add cells to phenol red broth - Seal using amojel ->
creates anaerobic environment Results: - Yellow: glucose is fermented and acid
is produced - Pushed up plug/bubble: gas was produced ***Remember to keep a
control without carbon source (e.g. glucose) -> should remain red
Question 7.
Why do we use King's agar B and not S1 for the Fluorescent Pigment Test?
Correct Answer: Pigment production on both the S1 plate and the King's agar B
plate will produce a yellow-green color. S1 media, however, contains a
detergent that interferes with the cell membrane of gram positive bacteria,
preventing their growth, and an antibiotic that kills facultative anaerobic gram
negative bacteria. King's agar B is not selective and, therefore, can be used on
more types of bacteria. King's agar B contains phosphorus and magnesium
which is known to increase production of the fluorescent pigment. King's agar B
lacks compounds that inhibit the growth of certain types of organisms
Question 8.
endospore test
Correct Answer: determines whether organism can form spores
, Question 9.
Is the control used in the phenol red test is a positive or negative control? Does it use
media with glucose or without glucose? Is an organism or no organism inoculated?
Correct Answer: negative, without glucose, organism
Question 10.
How does a gram stain work?
Correct Answer: - crystal violet dye stains both gram positive and gram negative
cells - iodine forms a complex with crystal violet, increasing the size of the dye -
destainer (acetone/ethanol solution) washes out crystal violet while shrinking
pores of peptidoglycan cell wall and permeabilizes lipid outer membrane of
gram negative cells -> traps crystal violet in gram positive cells -> it remains
purple while the gram positive cells are colorless - Safranin-O stains both gram
positive and negative cells, but is u detectable underneath the purple in gram
positive cells -> gram positive is purple, gram negative is pink
Question 11.
Name the two classes of microorganisms (classification based on oxygen consumption)
that utilize oxygen to produce chemical energy (ATP) through the electron transport chain.
Correct Answer: strict aerobes and facultative anaerobes
Question 12.
peptones
Correct Answer: unknown components; nutrient rich extracts from milk, yeast,
beef, etc.
Question 13.
purpose of ABA DABA process
Correct Answer: initial identification of the organism; either gives you the family
or genus of the bacterium
Question 14.
example of differential media
Correct Answer: MacConkey agar: contains pH indicator neutral red - organisms
that ferment lactose (sugar in the media) produce an acid end product -> lowers
pH -> turns red - organisms that do not ferment lactose remain colorless
Question 15.
differential media
Correct Answer: allows one to distinguish between different types of bacteria
growing on a single plate - colored dyes taken up by specific organisms - pH
indicators that alter the color of media surrounding a colony depending on the
secretion
Question 16.
dye in oxidase paper
Correct Answer: N,N-dimethyl phenylenediamine
