BIOD 171 MODULE 3 EXAM SCRIPT WITH
VERIFIED ANSWERS
◉ True or False: Differential media is best suited for
distinguishing between two similar
species of bacteria.
Answer: True
Growth media does not contain restricive factors, while selective
media is best used
to encourage the growth of one microbe while simultaneously
discouraging the
growth of the other. Since two similar species of microbes are
being studied they
must be differentiated under similar but just slightly different
conditions (differential
media).
◉ A researcher is asked to determine if a sample contains
Neisseria meningitides. Knowing Neisseria meningitides is slow
growing and other foreign microbes may also be present in the
culture, which type of media would be best suited?
Answer: Selectiva Media
,Selective media. If additional foreign microbes may be present in
your sample and
you know Neisseria meningitides is slow growing, you must
restrict the unwanted
microbes while supporting the growth of Neisseria meningitides.
Thus, you are
selectively encouraging one microbes growth, while selectively
restricting others.
◉ T/F: LB agar is classified as a selective, non-differential media
Answer: False
LB agar is the most basic type of agar and like LB, supports the
growth of virtually all microbes without restriction
◉ An unknown microbe is streaked onto a MacConkey agar plate.
After an overnight incubation at 37°C, growth is observed. Would
a Gram stain be necessary? Why or why not?
Answer: No, a gram stain would not be necessary, bc only gram-
negative microbes will grow on a MacConkey agar
◉ Which type of agar media is best suited to support the growth
of Staphylococcus?
Answer: Mannitol salt agar
, ◉ True or False: The visualization of colonies on a petri dish
represents bacterial cells that have multiplied ~2-3 times.
Answer: False
When an individual colony is visible on agar, the bacterial cell has
multiplied often a million times over
◉ True or False. The purpose of a quadrant streak is to produce
individual colonies of a bacterial population.
Answer: True
◉ True or False. When performing a dilution streak a new (or
sterilized) loop is not required for each phase as long as the
bacterial culture is pure.
Answer: False
a new or sterilized loop is absolutely required for each phase
◉ The number of phases (3 vs. 4) and/or the number of times a
loop passes through a previous phase (once vs. multiple times) is
acceptable provided what happens?
Answer: Either is acceptable provided that the resulting quadrant
contains growth of individual colonies within it and if it doesn't,
the experiment has to be redone.
◉ What is agar used for in microbiology?
VERIFIED ANSWERS
◉ True or False: Differential media is best suited for
distinguishing between two similar
species of bacteria.
Answer: True
Growth media does not contain restricive factors, while selective
media is best used
to encourage the growth of one microbe while simultaneously
discouraging the
growth of the other. Since two similar species of microbes are
being studied they
must be differentiated under similar but just slightly different
conditions (differential
media).
◉ A researcher is asked to determine if a sample contains
Neisseria meningitides. Knowing Neisseria meningitides is slow
growing and other foreign microbes may also be present in the
culture, which type of media would be best suited?
Answer: Selectiva Media
,Selective media. If additional foreign microbes may be present in
your sample and
you know Neisseria meningitides is slow growing, you must
restrict the unwanted
microbes while supporting the growth of Neisseria meningitides.
Thus, you are
selectively encouraging one microbes growth, while selectively
restricting others.
◉ T/F: LB agar is classified as a selective, non-differential media
Answer: False
LB agar is the most basic type of agar and like LB, supports the
growth of virtually all microbes without restriction
◉ An unknown microbe is streaked onto a MacConkey agar plate.
After an overnight incubation at 37°C, growth is observed. Would
a Gram stain be necessary? Why or why not?
Answer: No, a gram stain would not be necessary, bc only gram-
negative microbes will grow on a MacConkey agar
◉ Which type of agar media is best suited to support the growth
of Staphylococcus?
Answer: Mannitol salt agar
, ◉ True or False: The visualization of colonies on a petri dish
represents bacterial cells that have multiplied ~2-3 times.
Answer: False
When an individual colony is visible on agar, the bacterial cell has
multiplied often a million times over
◉ True or False. The purpose of a quadrant streak is to produce
individual colonies of a bacterial population.
Answer: True
◉ True or False. When performing a dilution streak a new (or
sterilized) loop is not required for each phase as long as the
bacterial culture is pure.
Answer: False
a new or sterilized loop is absolutely required for each phase
◉ The number of phases (3 vs. 4) and/or the number of times a
loop passes through a previous phase (once vs. multiple times) is
acceptable provided what happens?
Answer: Either is acceptable provided that the resulting quadrant
contains growth of individual colonies within it and if it doesn't,
the experiment has to be redone.
◉ What is agar used for in microbiology?
