BIO 250 Final Exam V2 | BIO 250 Microbiology | Actual Q&A
with Rationale (BIO250 Final Exam) | StraighterLine
1. Which of the following components are found in the cell wall of a Gram-positive
bacterium? (Select all that apply)
A. Lipopolysaccharide
B. Periplasmic space
C. Thick peptidoglycan layer and Teichoic acids
D. Outer membrane
E. Porin proteins
F. Mycolic acids
Correct Answer: C
Explanation: Gram-positive bacteria are characterized by a dense, multi-layered
peptidoglycan lattice that provides significant structural integrity. Teichoic acids are
embedded within this layer, functioning in cell wall maintenance and contributing to the
overall negative charge of the cell surface. Unlike Gram-negative organisms, they lack the
complex outer membrane and lipopolysaccharide components.
2. What is the primary function of the bacterial endospore?
A. To facilitate rapid reproduction in nutrient-rich environments.
B. To increase the surface area for nutrient absorption.
C. To serve as a primary site for metabolic activity and ATP production.
D. Survival of the genetic material during extreme environmental stress.
Correct Answer: D
Explanation: Endospores are highly resistant, dormant structures produced by certain
genera like Bacillus and Clostridium in response to harsh conditions. They protect the
bacterial DNA from heat, radiation, and chemical disinfectants for extended periods. This
process is not a form of reproduction but rather a specialized survival mechanism for the
organism.
3. During which phase of the bacterial growth curve are cells dividing at a maximal and
constant rate?
A. Lag phase
B. Log (Exponential) phase
,C. Stationary phase
D. Death (Decline) phase
Correct Answer: B
Explanation: The log phase is the period where the population increases exponentially as
cells are metabolically active and dividing at their generation time. During this time, the
growth rate is constant and the population is most uniform chemically and physiologically.
This phase is typically when bacteria are most susceptible to antimicrobial agents that
interfere with cell wall synthesis or protein production.
4. A standard autoclave cycle typically uses which of the following parameters to ensure
sterilization?
A. 100°C at 10 psi for 10 minutes
B. 63°C for 30 minutes
C. 121°C at 15 psi for 15-20 minutes
D. 160°C for 2 hours
Correct Answer: C
Explanation: Sterilization in an autoclave is achieved through pressurized steam, which
allows temperatures to rise above the boiling point of water. The standard setting of 121°C
at 15 psi is sufficient to destroy even the most heat-resistant endospores within 15 to 20
minutes. Lower temperatures used in pasteurization or boiling are insufficient to achieve
true sterilization.
5. Which enzyme is responsible for synthesizing a short RNA primer to initiate DNA
replication?
A. Primase
B. Helicase
C. Ligase
D. DNA Polymerase III
Correct Answer: A
Explanation: DNA polymerase requires a free 3’-OH group to begin adding nucleotides,
which it cannot provide itself. Primase, a type of RNA polymerase, solves this by creating a
short RNA sequence complementary to the DNA template. Once this primer is in place, DNA
polymerase III can extend the new DNA strand.
6. Which of the following describes a facultative anaerobe?
A. An organism that requires high levels of CO2 for growth.
, B. An organism that requires a small amount of oxygen but is inhibited by atmospheric
levels.
C. An organism that is killed by the presence of oxygen.
D. An organism that can grow with or without oxygen but grows better with it.
Correct Answer: D
Explanation: Facultative anaerobes possess the metabolic flexibility to perform both
aerobic respiration and fermentation or anaerobic respiration. While they can survive in
the absence of oxygen, they produce significantly more ATP through aerobic pathways,
resulting in faster growth when oxygen is present. Common examples include Escherichia
coli and various species of Staphylococcus.
7. What is the net gain of ATP from one molecule of glucose during glycolysis?
A. 1 ATP
B. 36-38 ATP
C. 4 ATP
D. 2 ATP
Correct Answer: D
Explanation: Glycolysis consists of an energy-investment phase and an energy-payoff
phase. While 4 ATP molecules are produced total, 2 ATP are consumed at the start of the
process, leaving a net profit of 2 ATP. This process also produces 2 molecules of NADH and
2 pyruvate molecules per glucose.
8. Which class of immunoglobulin is the only one capable of crossing the placenta to provide
passive immunity to the fetus?
A. IgA
B. IgM
C. IgD
D. IgE
E. IgG
Correct Answer: E
Explanation: IgG is the most abundant antibody in the blood and has a structure that
allows it to pass through the placental barrier. This provides the developing fetus with
protection against pathogens the mother has previously encountered. This form of
naturally acquired passive immunity is vital during the first few months of an infant’s life.
with Rationale (BIO250 Final Exam) | StraighterLine
1. Which of the following components are found in the cell wall of a Gram-positive
bacterium? (Select all that apply)
A. Lipopolysaccharide
B. Periplasmic space
C. Thick peptidoglycan layer and Teichoic acids
D. Outer membrane
E. Porin proteins
F. Mycolic acids
Correct Answer: C
Explanation: Gram-positive bacteria are characterized by a dense, multi-layered
peptidoglycan lattice that provides significant structural integrity. Teichoic acids are
embedded within this layer, functioning in cell wall maintenance and contributing to the
overall negative charge of the cell surface. Unlike Gram-negative organisms, they lack the
complex outer membrane and lipopolysaccharide components.
2. What is the primary function of the bacterial endospore?
A. To facilitate rapid reproduction in nutrient-rich environments.
B. To increase the surface area for nutrient absorption.
C. To serve as a primary site for metabolic activity and ATP production.
D. Survival of the genetic material during extreme environmental stress.
Correct Answer: D
Explanation: Endospores are highly resistant, dormant structures produced by certain
genera like Bacillus and Clostridium in response to harsh conditions. They protect the
bacterial DNA from heat, radiation, and chemical disinfectants for extended periods. This
process is not a form of reproduction but rather a specialized survival mechanism for the
organism.
3. During which phase of the bacterial growth curve are cells dividing at a maximal and
constant rate?
A. Lag phase
B. Log (Exponential) phase
,C. Stationary phase
D. Death (Decline) phase
Correct Answer: B
Explanation: The log phase is the period where the population increases exponentially as
cells are metabolically active and dividing at their generation time. During this time, the
growth rate is constant and the population is most uniform chemically and physiologically.
This phase is typically when bacteria are most susceptible to antimicrobial agents that
interfere with cell wall synthesis or protein production.
4. A standard autoclave cycle typically uses which of the following parameters to ensure
sterilization?
A. 100°C at 10 psi for 10 minutes
B. 63°C for 30 minutes
C. 121°C at 15 psi for 15-20 minutes
D. 160°C for 2 hours
Correct Answer: C
Explanation: Sterilization in an autoclave is achieved through pressurized steam, which
allows temperatures to rise above the boiling point of water. The standard setting of 121°C
at 15 psi is sufficient to destroy even the most heat-resistant endospores within 15 to 20
minutes. Lower temperatures used in pasteurization or boiling are insufficient to achieve
true sterilization.
5. Which enzyme is responsible for synthesizing a short RNA primer to initiate DNA
replication?
A. Primase
B. Helicase
C. Ligase
D. DNA Polymerase III
Correct Answer: A
Explanation: DNA polymerase requires a free 3’-OH group to begin adding nucleotides,
which it cannot provide itself. Primase, a type of RNA polymerase, solves this by creating a
short RNA sequence complementary to the DNA template. Once this primer is in place, DNA
polymerase III can extend the new DNA strand.
6. Which of the following describes a facultative anaerobe?
A. An organism that requires high levels of CO2 for growth.
, B. An organism that requires a small amount of oxygen but is inhibited by atmospheric
levels.
C. An organism that is killed by the presence of oxygen.
D. An organism that can grow with or without oxygen but grows better with it.
Correct Answer: D
Explanation: Facultative anaerobes possess the metabolic flexibility to perform both
aerobic respiration and fermentation or anaerobic respiration. While they can survive in
the absence of oxygen, they produce significantly more ATP through aerobic pathways,
resulting in faster growth when oxygen is present. Common examples include Escherichia
coli and various species of Staphylococcus.
7. What is the net gain of ATP from one molecule of glucose during glycolysis?
A. 1 ATP
B. 36-38 ATP
C. 4 ATP
D. 2 ATP
Correct Answer: D
Explanation: Glycolysis consists of an energy-investment phase and an energy-payoff
phase. While 4 ATP molecules are produced total, 2 ATP are consumed at the start of the
process, leaving a net profit of 2 ATP. This process also produces 2 molecules of NADH and
2 pyruvate molecules per glucose.
8. Which class of immunoglobulin is the only one capable of crossing the placenta to provide
passive immunity to the fetus?
A. IgA
B. IgM
C. IgD
D. IgE
E. IgG
Correct Answer: E
Explanation: IgG is the most abundant antibody in the blood and has a structure that
allows it to pass through the placental barrier. This provides the developing fetus with
protection against pathogens the mother has previously encountered. This form of
naturally acquired passive immunity is vital during the first few months of an infant’s life.
