MCB2010L FINAL EXAM WITH CORRECT
ACTUAL QUESTIONS AND CORRECTLY
WELL DEFINED ANSWERS LATEST 2024 –
2025 ALREADY GRADED A+
How are results for MAC agar interpreted? - ANSWERS--Poor growth or
no growth: organism is inhibited by crystal violet and/or bile; Gram-
positive
-Good growth: organism is not inhibited by crystal violet or bile; Gram-
negative
-Pink to red growth with or without bile precipitate: organism produced
acid from lactose fermentation; probably coliform
-Growth is "colourless" (not red or pink): organism does not ferment
lactose; noncoliform
What is the electron transport chain (ETC)? - ANSWERS-ETCs of aerobic
and facultatively anaerobic bacteria are composed of molecules
capable of accepting and donating electrons as conditions dictate. As
such, these molecules alternate between the oxidized and reduced
forms, passing electrons down the chain to the final electron acceptor,
,oxygen. Energy lost by electrons in this sequential transfer is used to
perform oxidative phosphorylation (i.e., produce ATP from ADP).
Flavoprotein - ANSWERS-In most cases, electrons in the aerobic ETC
follow the step-wise path to oxygen, but other paths can be followed
and these result in toxic forms of reduced oxygen. ETC carrier molecule
called flavoprotein can bypass the next carrier in the chain and transfer
electrons directly to oxygen, which produces hydrogen peroxide, a
highly potent cellular toxin. FADH2 is capable of the same reaction.
Even if the electrons follow the complete ETC, another toxin, the
superoxide radical (O2-), can be produced in the final step because
electrons can reduce oxygen one at a time and sometimes it is released
before it is completely reduced to H2O. H2O2 and O2- are toxic
because they oxidize biochemicals and make them nonfunctional.
Organisms that produce them also have enzymes that can break them
down.
What is the application of FTB? - ANSWERS-Can be modified to
promote growth of a wide variety of fastidious to non fastidious
microorganisms. It can be used to illustrate microbial growth
representing all levels of oxygen tolerance. However, it generally is
associated with the cultivation of anaerobic and microaerophilic
bacteria.
,Why is it preferred to use fresh FTB medium over old medium? -
ANSWERS-Oxygen removed during autoclaving will diffuse back into the
medium as the tubes cool to room temperature. This produces a
gradient of concentrations from aerobic (comparable to air) at the top
to anaerobic at the bottom. Fresh media will appear clear to straw
coloured with a pink region at the top, where the dye has become
oxidized. The use of old medium will cause the aerobic region of the
tube to grow, indicating widespread oxidation throughout the tube.
Where would you expect to see growth on FTB medium of a strict
aerobe, anaerobe, microaerophile, facultative anaerobe, and an
aerotolerant anaerobe? - ANSWERS--Strict aerobe: at the top of the
broth, where oxygen is abundant
-Anaerobe: at the bottom of the broth, where oxygen is not present
-Microaerophile: in the middle of the broth where oxygen is present,
but not in large amounts
-Facultative anaerobe: concentrated at the top (grows best when most
oxygen is present), but spread throughout (can grow anaerobically)
-Aerotolerant anaerobe: growth relatively evenly throughout
(anaerobic, but tolerates oxygen presence)
Consider resazurin dye. Considering the major application of this
medium, which is more desirable, a thick coloured or a thin coloured
band? - ANSWERS-A thin coloured band would be more desirable, as it
would indicate that the medium is more fresh. The older the medium,
, the more oxidation occurs within the media, creating the indicator
band to expand. Certain bacteria will not be able to grow or the results
of their growth will become skewed.
Where is the resazurin located in the broth column? - ANSWERS-At the
very top of the broth, forming a band.
Why is the FTB broth pink at the surface of the medium? - ANSWERS-
This is where the most oxygen is present.
Which type of organism would most likely be affected negatively by the
use of old FTB media? - ANSWERS-Strict (obligate) anaerobes; these
organisms are inhibited by the presence of oxygen, therefore an
abundance of oxygen in the tube may produce limited growth by these
organisms.
Which type of organism would most likely be positively affected by the
use of old FTB media? - ANSWERS-Strict (obligate) aerobes; the
abundance of oxygen in the media will provide a tremendous
advantage to these organism's growth, as they need sufficient amounts
of oxygen to produce.
What is fluid thioglycollate broth (FTB)? - ANSWERS-It is prepared as a
basic medium or with a variety of substances, depending on the needs
ACTUAL QUESTIONS AND CORRECTLY
WELL DEFINED ANSWERS LATEST 2024 –
2025 ALREADY GRADED A+
How are results for MAC agar interpreted? - ANSWERS--Poor growth or
no growth: organism is inhibited by crystal violet and/or bile; Gram-
positive
-Good growth: organism is not inhibited by crystal violet or bile; Gram-
negative
-Pink to red growth with or without bile precipitate: organism produced
acid from lactose fermentation; probably coliform
-Growth is "colourless" (not red or pink): organism does not ferment
lactose; noncoliform
What is the electron transport chain (ETC)? - ANSWERS-ETCs of aerobic
and facultatively anaerobic bacteria are composed of molecules
capable of accepting and donating electrons as conditions dictate. As
such, these molecules alternate between the oxidized and reduced
forms, passing electrons down the chain to the final electron acceptor,
,oxygen. Energy lost by electrons in this sequential transfer is used to
perform oxidative phosphorylation (i.e., produce ATP from ADP).
Flavoprotein - ANSWERS-In most cases, electrons in the aerobic ETC
follow the step-wise path to oxygen, but other paths can be followed
and these result in toxic forms of reduced oxygen. ETC carrier molecule
called flavoprotein can bypass the next carrier in the chain and transfer
electrons directly to oxygen, which produces hydrogen peroxide, a
highly potent cellular toxin. FADH2 is capable of the same reaction.
Even if the electrons follow the complete ETC, another toxin, the
superoxide radical (O2-), can be produced in the final step because
electrons can reduce oxygen one at a time and sometimes it is released
before it is completely reduced to H2O. H2O2 and O2- are toxic
because they oxidize biochemicals and make them nonfunctional.
Organisms that produce them also have enzymes that can break them
down.
What is the application of FTB? - ANSWERS-Can be modified to
promote growth of a wide variety of fastidious to non fastidious
microorganisms. It can be used to illustrate microbial growth
representing all levels of oxygen tolerance. However, it generally is
associated with the cultivation of anaerobic and microaerophilic
bacteria.
,Why is it preferred to use fresh FTB medium over old medium? -
ANSWERS-Oxygen removed during autoclaving will diffuse back into the
medium as the tubes cool to room temperature. This produces a
gradient of concentrations from aerobic (comparable to air) at the top
to anaerobic at the bottom. Fresh media will appear clear to straw
coloured with a pink region at the top, where the dye has become
oxidized. The use of old medium will cause the aerobic region of the
tube to grow, indicating widespread oxidation throughout the tube.
Where would you expect to see growth on FTB medium of a strict
aerobe, anaerobe, microaerophile, facultative anaerobe, and an
aerotolerant anaerobe? - ANSWERS--Strict aerobe: at the top of the
broth, where oxygen is abundant
-Anaerobe: at the bottom of the broth, where oxygen is not present
-Microaerophile: in the middle of the broth where oxygen is present,
but not in large amounts
-Facultative anaerobe: concentrated at the top (grows best when most
oxygen is present), but spread throughout (can grow anaerobically)
-Aerotolerant anaerobe: growth relatively evenly throughout
(anaerobic, but tolerates oxygen presence)
Consider resazurin dye. Considering the major application of this
medium, which is more desirable, a thick coloured or a thin coloured
band? - ANSWERS-A thin coloured band would be more desirable, as it
would indicate that the medium is more fresh. The older the medium,
, the more oxidation occurs within the media, creating the indicator
band to expand. Certain bacteria will not be able to grow or the results
of their growth will become skewed.
Where is the resazurin located in the broth column? - ANSWERS-At the
very top of the broth, forming a band.
Why is the FTB broth pink at the surface of the medium? - ANSWERS-
This is where the most oxygen is present.
Which type of organism would most likely be affected negatively by the
use of old FTB media? - ANSWERS-Strict (obligate) anaerobes; these
organisms are inhibited by the presence of oxygen, therefore an
abundance of oxygen in the tube may produce limited growth by these
organisms.
Which type of organism would most likely be positively affected by the
use of old FTB media? - ANSWERS-Strict (obligate) aerobes; the
abundance of oxygen in the media will provide a tremendous
advantage to these organism's growth, as they need sufficient amounts
of oxygen to produce.
What is fluid thioglycollate broth (FTB)? - ANSWERS-It is prepared as a
basic medium or with a variety of substances, depending on the needs
