BIO 171 BASIC MICROBIOLOGY FINAL
PRACTICE EXAM
1. Which component of the Gram-negative cell wall is specifically responsible for the
induction of septic shock?
A. Teichoic acid
B. Lipopolysaccharide (Lipid A)
C. Peptidoglycan
D. Porin proteins
Answer: B
Conceptual Explanation: Lipid A, a component of the Lipopolysaccharide (LPS) in the
outer membrane of Gram-negative bacteria, acts as an endotoxin that can trigger a massive
immune response leading to septic shock.
2. During which phase of the bacterial growth curve are cells most metabolically active and
sensitive to antibiotics like penicillin?
A. Lag phase
B. Stationary phase
C. Log (Exponential) phase
,D. Death phase
Answer: C
Conceptual Explanation: During the log phase, bacteria are rapidly dividing and
synthesizing new cell walls, making them highly susceptible to beta-lactam antibiotics that
inhibit peptidoglycan synthesis.
3. In aerobic respiration, what is the final electron acceptor in the electron transport chain?
A. Nitrate
B. Oxygen (O2)
C. Pyruvate
D. Sulfate
Answer: B
Conceptual Explanation: Aerobic respiration uses molecular oxygen as the final electron
acceptor, which is then reduced to water.
4. Which enzyme is responsible for relieving torsional strain (supercoiling) ahead of the
replication fork during DNA replication?
A. DNA Helicase
B. DNA Polymerase I
C. DNA Gyrase (Topoisomerase)
D. Primase
, Answer: C
Conceptual Explanation: DNA Gyrase travels ahead of the replication fork and introduces
negative supercoils to counteract the positive supercoiling caused by helicase unwinding
the DNA.
5. A technician performs a Gram stain but forgets the decolorizer step (alcohol). What will be
the appearance of Gram-negative bacteria?
A. Pink/Red
B. Purple
C. Colorless
D. Brown
Answer: B
Conceptual Explanation: Without the decolorizer, the primary stain (Crystal Violet) is not
removed from the Gram-negative cells, causing them to remain purple regardless of their
cell wall structure.
6. Which of the following describes a bacterial cell that has a single flagellum at one pole?
A. Peritrichous
B. Monotrichous
C. Lophotrichous
D. Amphitrichous
PRACTICE EXAM
1. Which component of the Gram-negative cell wall is specifically responsible for the
induction of septic shock?
A. Teichoic acid
B. Lipopolysaccharide (Lipid A)
C. Peptidoglycan
D. Porin proteins
Answer: B
Conceptual Explanation: Lipid A, a component of the Lipopolysaccharide (LPS) in the
outer membrane of Gram-negative bacteria, acts as an endotoxin that can trigger a massive
immune response leading to septic shock.
2. During which phase of the bacterial growth curve are cells most metabolically active and
sensitive to antibiotics like penicillin?
A. Lag phase
B. Stationary phase
C. Log (Exponential) phase
,D. Death phase
Answer: C
Conceptual Explanation: During the log phase, bacteria are rapidly dividing and
synthesizing new cell walls, making them highly susceptible to beta-lactam antibiotics that
inhibit peptidoglycan synthesis.
3. In aerobic respiration, what is the final electron acceptor in the electron transport chain?
A. Nitrate
B. Oxygen (O2)
C. Pyruvate
D. Sulfate
Answer: B
Conceptual Explanation: Aerobic respiration uses molecular oxygen as the final electron
acceptor, which is then reduced to water.
4. Which enzyme is responsible for relieving torsional strain (supercoiling) ahead of the
replication fork during DNA replication?
A. DNA Helicase
B. DNA Polymerase I
C. DNA Gyrase (Topoisomerase)
D. Primase
, Answer: C
Conceptual Explanation: DNA Gyrase travels ahead of the replication fork and introduces
negative supercoils to counteract the positive supercoiling caused by helicase unwinding
the DNA.
5. A technician performs a Gram stain but forgets the decolorizer step (alcohol). What will be
the appearance of Gram-negative bacteria?
A. Pink/Red
B. Purple
C. Colorless
D. Brown
Answer: B
Conceptual Explanation: Without the decolorizer, the primary stain (Crystal Violet) is not
removed from the Gram-negative cells, causing them to remain purple regardless of their
cell wall structure.
6. Which of the following describes a bacterial cell that has a single flagellum at one pole?
A. Peritrichous
B. Monotrichous
C. Lophotrichous
D. Amphitrichous
