BIOD 171 Module 4 Exam with complete
solutions
BIOD 171 Module 4 Exam with complete
solutions
What is another name for a liquid growth media, and what are the basic components? -
CORRECT ANSWER Growth media in a liquid form is often referred to as nutrient
broth. As the name implies its composition consists primarily of essential 'ingredients'
such as a rich source of sugars, amino acids, and vitamins. Together, a nutrient broth
provides the microbe with a source of carbon/energy, which, in turn, encourages its
expansion.
What is selective media? - CORRECT ANSWER Selective media allows for only the
growth of certain microbes while restricting the growth of all others.
What is differential media? - CORRECT ANSWER Differential media is used to
distinguish between two (or more) related microbes.
What are the requirements of a fastidious microbe? - CORRECT ANSWER A fastidious
microbe is an organism with complex growth requirements such that if absent it will not
grow. Enriched medias thus contain these specific and essential nutrients required for
the growth of a particular subset of microorganisms.
What is agar? - CORRECT ANSWER In its simplest form agar is liquid growth media
that has had a hardening agent added to it. Agar is created when a polysaccharide
derived from seaweed (algae) extract is added to growth media. Agar is used to create
a solid, smooth surface on which microbes can grow.
LB agar is classified as a non-selective, differential media
True
False - CORRECT ANSWER False
LB agar is non-selective and non-differential
What are the three forms of hemolysis found on blood agar plates? - CORRECT
ANSWER Alpha hemolysis, beta hemolysis, and gamma hemolysis
Alpha hemolysis - CORRECT ANSWER Presents with greenish-brown color on blood
agar due to the partial lysis of red blood cells
Beta hemolysis - CORRECT ANSWER Clear zones on blood agar indicate beta
hemolysis, which is the complete lysis of red blood cells
, BIOD 171 Module 4 Exam with complete
solutions
Gamma hemolysis - CORRECT ANSWER Presents a white/tan on blood agar due to
the lack of hemolytic activity.
What is the primary purpose of Columbia CNA agar? - CORRECT ANSWER As it
suppresses the growth of Gram-negative bacteria CNA agar is, therefore, used for
isolation of Gram-positive microbes.
Name the type of plate derived from BAP that contains lysed red blood cells -
CORRECT ANSWER Lysed red blood cells (RBCs) are a primary component in the
formulation of Chocolate agar.
Define the selective and differential abilities of a MacConkey agar plate - CORRECT
ANSWER MacConkey agar is selective in that only Gram-negative microbes will grow
on the agar -Gram-positive microbes simply do not grow. MacConkey agar is also
considered a differential media as it distinguishes between microbes capable of
fermenting lactose (red colonies) and those that are non-fermenters (white/tan
colonies).
What colors would you expect to see on an EMB plate containing E. coli? - CORRECT
ANSWER The EMB plate itself is red in color while in the presence of E. coli, the
growing colonies will take on a distinctive metallic green sheen.
What is the name of the process of spreading a bacterial culture onto a petri dish? -
CORRECT ANSWER Plating. Plating microbes can be done using a sterile loop, a
sterile swab, or a sterilized wire loop. Each device is simply a means of spreading the
bacteria, most commonly in a simple back-and-forth motion, across the plate.
What is the primary advantage of plating a bacterial culture as opposed to having it
grow in solution? - CORRECT ANSWER The primary advantage of plating a bacterial
sample onto agar is that cells are held in place. Unlike in a nutrient broth where
bacterial cells can multiply but are free to move around in solution, bacteria plated onto
agar are fixed in such a way as to support the formation and visualization of colonies.
What is the purpose of the quadrant streak approach? - CORRECT ANSWER The
purpose of this method is to generate an individual colony so that a single (pure)
bacterial sample can be picked from the plate.
In a three-phase dilution gradient, which phase most likely contains individual colonies:
phase 1 (P1) or phase 3 (P3)? - CORRECT ANSWER Individual colonies are most
likely going to appear within the phase 3 streaks. You being with P1 (highest
concentration), dilute during P2 and then further dilute the sample in P3. However, it is
possible to see individual colonies in P2 if only a small portion of P1 was carried over
into P2.
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