MCB 3020C Final Exam V1 | MCB 3020C General Microbiology | Actual
Q&A with Rationale (MCB3020C Final Exam) | University of Central
Florida
1. Which of the following structures is uniquely found in Gram-negative bacteria and contains
Lipid A?
A. Peptidoglycan
B. Teichoic acid
C. Periplasmic space
D. Lipopolysaccharide (LPS)
Answer: D
Explanation: Lipopolysaccharide (LPS) is a major component of the outer membrane of
Gram-negative bacteria, consisting of O-antigen, a core polysaccharide, and Lipid A. Lipid A
acts as an endotoxin that can trigger severe immune responses and septic shock in the host.
This structure distinguishes Gram-negative organisms from Gram-positive organisms,
which lack an outer membrane.
2. In the process of glycolysis, what is the net gain of ATP per molecule of glucose via
substrate-level phosphorylation?
A. 2 ATP
B. 1 ATP
C. 4 ATP
D. 38 ATP
Answer: A
Explanation: During glycolysis, a total of four ATP molecules are produced; however, two
ATP molecules are consumed during the initial energy investment phase. This results in a
net yield of two ATP molecules for the cell to use for metabolic work. This specific energy
capture occurs through substrate-level phosphorylation rather than the electron transport
chain.
3. Which scientist is credited with definitively disproving the theory of spontaneous
generation using swan-necked flasks?
A. Robert Koch
B. Antonie van Leeuwenhoek
C. Louis Pasteur
,D. Joseph Lister
Answer: C
Explanation: Louis Pasteur utilized swan-necked flasks to demonstrate that
microorganisms in the air were responsible for contaminating infusions, rather than life
arising spontaneously. The curved neck allowed air to enter but trapped dust and
microbes, keeping the broth sterile until the flask was tilted. This landmark experiment
solidified the theory of biogenesis, stating that life only comes from pre-existing life.
4. What is the primary function of the bacterial endospore?
A. Reproduction
B. Attachment to host tissues
C. Storage of nutrients
D. Survival during harsh environmental conditions
Answer: D
Explanation: Bacterial endospores are highly resistant, dormant structures produced by
certain genera like Bacillus and Clostridium in response to nutrient depletion. They are
designed to withstand extreme temperatures, radiation, and chemical disinfectants for
extended periods. Unlike fungal spores, bacterial endospores are not a means of
reproduction but a mechanism for long-term survival.
5. Which enzyme is responsible for unwinding the DNA double helix during the initiation of
replication?
A. DNA Polymerase III
B. DNA Ligase
C. Topoisomerase
D. Helicase
Answer: D
Explanation: Helicase acts at the origin of replication by breaking the hydrogen bonds
between the complementary nitrogenous bases of the DNA strands. This action creates the
replication fork, allowing other enzymes to access the single-stranded templates. Without
helicase activity, the double-stranded DNA would remain tightly coiled and inaccessible for
replication.
6. Which type of horizontal gene transfer involves the uptake of ‘naked’ DNA from the
surrounding environment?
A. Conjugation
B. Transformation
, C. Transduction
D. Transposition
Answer: B
Explanation: Transformation is the process by which a competent bacterial cell
incorporates exogenous DNA fragments released by lysed cells into its own genome. This
mechanism was first famously described by Frederick Griffith in his experiments with
Streptococcus pneumoniae. It is distinct from conjugation, which requires cell-to-cell
contact, and transduction, which requires a viral vector.
7. A psychrophile would be expected to grow best at which of the following temperatures?
A. 37°C
B. 10°C
C. 60°C
D. 95°C
Answer: B
Explanation: Psychrophiles are extremophilic organisms that are capable of growth and
reproduction in cold temperatures, typically ranging from -15°C to 20°C. They possess
specialized enzymes and membranes that remain functional and fluid in near-freezing
conditions. In contrast, mesophiles prefer moderate temperatures around human body
heat (37°C), while thermophiles thrive in heat.
8. During the stationary phase of a bacterial growth curve, which of the following occurs?
A. The population is increasing exponentially.
B. Cells are adjusting to a new environment without dividing.
C. The rate of cell death equals the rate of new cell formation.
D. Toxic waste products are absent from the medium.
Answer: C
Explanation: In the stationary phase, the number of viable cells remains constant because
the growth rate slows down to match the death rate. This equilibrium is usually reached
due to the depletion of essential nutrients and the accumulation of inhibitory metabolic
waste products. It follows the log (exponential) phase and precedes the death phase in a
batch culture.
9. Which of the following describes a microaerophile?
A. It requires high concentrations of oxygen to grow.
B. It requires oxygen at a lower concentration than is present in the atmosphere.
Q&A with Rationale (MCB3020C Final Exam) | University of Central
Florida
1. Which of the following structures is uniquely found in Gram-negative bacteria and contains
Lipid A?
A. Peptidoglycan
B. Teichoic acid
C. Periplasmic space
D. Lipopolysaccharide (LPS)
Answer: D
Explanation: Lipopolysaccharide (LPS) is a major component of the outer membrane of
Gram-negative bacteria, consisting of O-antigen, a core polysaccharide, and Lipid A. Lipid A
acts as an endotoxin that can trigger severe immune responses and septic shock in the host.
This structure distinguishes Gram-negative organisms from Gram-positive organisms,
which lack an outer membrane.
2. In the process of glycolysis, what is the net gain of ATP per molecule of glucose via
substrate-level phosphorylation?
A. 2 ATP
B. 1 ATP
C. 4 ATP
D. 38 ATP
Answer: A
Explanation: During glycolysis, a total of four ATP molecules are produced; however, two
ATP molecules are consumed during the initial energy investment phase. This results in a
net yield of two ATP molecules for the cell to use for metabolic work. This specific energy
capture occurs through substrate-level phosphorylation rather than the electron transport
chain.
3. Which scientist is credited with definitively disproving the theory of spontaneous
generation using swan-necked flasks?
A. Robert Koch
B. Antonie van Leeuwenhoek
C. Louis Pasteur
,D. Joseph Lister
Answer: C
Explanation: Louis Pasteur utilized swan-necked flasks to demonstrate that
microorganisms in the air were responsible for contaminating infusions, rather than life
arising spontaneously. The curved neck allowed air to enter but trapped dust and
microbes, keeping the broth sterile until the flask was tilted. This landmark experiment
solidified the theory of biogenesis, stating that life only comes from pre-existing life.
4. What is the primary function of the bacterial endospore?
A. Reproduction
B. Attachment to host tissues
C. Storage of nutrients
D. Survival during harsh environmental conditions
Answer: D
Explanation: Bacterial endospores are highly resistant, dormant structures produced by
certain genera like Bacillus and Clostridium in response to nutrient depletion. They are
designed to withstand extreme temperatures, radiation, and chemical disinfectants for
extended periods. Unlike fungal spores, bacterial endospores are not a means of
reproduction but a mechanism for long-term survival.
5. Which enzyme is responsible for unwinding the DNA double helix during the initiation of
replication?
A. DNA Polymerase III
B. DNA Ligase
C. Topoisomerase
D. Helicase
Answer: D
Explanation: Helicase acts at the origin of replication by breaking the hydrogen bonds
between the complementary nitrogenous bases of the DNA strands. This action creates the
replication fork, allowing other enzymes to access the single-stranded templates. Without
helicase activity, the double-stranded DNA would remain tightly coiled and inaccessible for
replication.
6. Which type of horizontal gene transfer involves the uptake of ‘naked’ DNA from the
surrounding environment?
A. Conjugation
B. Transformation
, C. Transduction
D. Transposition
Answer: B
Explanation: Transformation is the process by which a competent bacterial cell
incorporates exogenous DNA fragments released by lysed cells into its own genome. This
mechanism was first famously described by Frederick Griffith in his experiments with
Streptococcus pneumoniae. It is distinct from conjugation, which requires cell-to-cell
contact, and transduction, which requires a viral vector.
7. A psychrophile would be expected to grow best at which of the following temperatures?
A. 37°C
B. 10°C
C. 60°C
D. 95°C
Answer: B
Explanation: Psychrophiles are extremophilic organisms that are capable of growth and
reproduction in cold temperatures, typically ranging from -15°C to 20°C. They possess
specialized enzymes and membranes that remain functional and fluid in near-freezing
conditions. In contrast, mesophiles prefer moderate temperatures around human body
heat (37°C), while thermophiles thrive in heat.
8. During the stationary phase of a bacterial growth curve, which of the following occurs?
A. The population is increasing exponentially.
B. Cells are adjusting to a new environment without dividing.
C. The rate of cell death equals the rate of new cell formation.
D. Toxic waste products are absent from the medium.
Answer: C
Explanation: In the stationary phase, the number of viable cells remains constant because
the growth rate slows down to match the death rate. This equilibrium is usually reached
due to the depletion of essential nutrients and the accumulation of inhibitory metabolic
waste products. It follows the log (exponential) phase and precedes the death phase in a
batch culture.
9. Which of the following describes a microaerophile?
A. It requires high concentrations of oxygen to grow.
B. It requires oxygen at a lower concentration than is present in the atmosphere.
