Microbiology BIO 420 Exam 1 | 2026 Verified Edition
Question 1
Which of the following best describes the primary function of the bacterial cell wall?
A) Facilitate DNA replication
B) Maintain cell shape and prevent osmotic lysis
C) Generate ATP through oxidative phosphorylation
D) Synthesize ribosomal RNA
ANSWER: B
Rationale A: Incorrect. DNA replication occurs in the nucleoid and is mediated by DNA
polymerase, not the cell wall.
Rationale B: Correct. The peptidoglycan layer provides structural integrity, preventing the
cell from bursting in hypotonic environments.
Rationale C: Incorrect. ATP synthesis occurs at the plasma membrane in prokaryotes via
the electron transport chain.
Rationale D: Incorrect. rRNA is synthesized in the cytoplasm by RNA polymerase.
Question 2
Gram-positive bacteria are characterized by which of the following features?
A) Thin peptidoglycan layer and outer membrane
B) Thick peptidoglycan layer and teichoic acids
C) Presence of lipopolysaccharide in the inner membrane
D) Absence of a plasma membrane
ANSWER: B
Rationale A: Incorrect. This describes the structure of Gram-negative bacteria.
,Rationale B: Correct. Gram-positive bacteria possess a thick, multi-layered peptidoglycan
wall interwoven with teichoic and lipoteichoic acids.
Rationale C: Incorrect. Lipopolysaccharide (LPS) is found exclusively in the outer
membrane of Gram-negative bacteria.
Rationale D: Incorrect. All living bacterial cells possess an inner plasma (cytoplasmic)
membrane.
Question 3
Which structure is essential for bacterial conjugation?
A) Flagellum
B) Capsule
C) Sex pilus
D) Endospore
ANSWER: C
Rationale A: Incorrect. Flagella are primarily responsible for cellular motility.
Rationale B: Incorrect. Capsules protect against phagocytosis and desiccation, not genetic
exchange.
Rationale C: Correct. The sex pilus (F pilus) mediates the initial contact and retraction to
bring donor and recipient cells together.
Rationale D: Incorrect. Endospores are dormant survival structures, not involved in active
DNA transfer.
Question 4
Endotoxins are associated with which component of bacteria?
A) Peptidoglycan
B) Teichoic acid
C) Lipopolysaccharide (LPS)
D) Exotoxin proteins
ANSWER: C
,Rationale A: Incorrect. Peptidoglycan can trigger inflammation but is not classified as an
endotoxin.
Rationale B: Incorrect. Teichoic acids are Gram-positive wall components and are not
endotoxins.
Rationale C: Correct. Lipid A, the toxic component of LPS in the Gram-negative outer
membrane, is the classic endotoxin.
Rationale D: Incorrect. Exotoxins are secreted proteins, distinct from structural endotoxins.
Question 5
What is the role of the enzyme lysozyme in host defense?
A) Degrades bacterial DNA
B) Hydrolyzes peptidoglycan in bacterial cell walls
C) Inhibits protein synthesis
D) Disrupts the outer membrane of Gram-negative bacteria
ANSWER: B
Rationale A: Incorrect. Nucleases degrade DNA, not lysozyme.
Rationale B: Correct. Lysozyme cleaves the β-1,4-glycosidic bonds between NAM and NAG
in peptidoglycan.
Rationale C: Incorrect. Lysozyme does not target ribosomes or protein synthesis machinery.
Rationale D: Incorrect. While it affects the underlying wall, it does not primarily disrupt the
LPS outer membrane.
Question 6
Which of the following bacteria is an obligate intracellular pathogen?
A) Escherichia coli
B) Staphylococcus aureus
C) Chlamydia trachomatis
D) Bacillus subtilis
ANSWER: C
, Rationale A: Incorrect. E. coli is a facultative anaerobe that grows easily on artificial media.
Rationale B: Incorrect. S. aureus is a free-living facultative anaerobe.
Rationale C: Correct. C. trachomatis cannot synthesize its own ATP and relies entirely on
host cell machinery.
Rationale D: Incorrect. B. subtilis is a common, free-living soil bacterium.
Question 7
The process by which bacteria take up free naked DNA from the environment is called:
A) Transduction
B) Conjugation
C) Transformation
D) Transposition
ANSWER: C
Rationale A: Incorrect. Transduction involves the transfer of bacterial DNA via a
bacteriophage vector.
Rationale B: Incorrect. Conjugation requires direct cell-to-cell contact via a pilus.
Rationale C: Correct. Transformation is the uptake of free environmental DNA by a
competent cell.
Rationale D: Incorrect. Transposition refers to the movement of "jumping genes" within a
genome.
Question 8
Which of the following is NOT a characteristic of archaea?
A) Ether-linked membrane lipids
B) Presence of peptidoglycan in cell walls
C) Ability to thrive in extreme environments
D) Distinct RNA polymerase more similar to eukaryotes
ANSWER: B
Question 1
Which of the following best describes the primary function of the bacterial cell wall?
A) Facilitate DNA replication
B) Maintain cell shape and prevent osmotic lysis
C) Generate ATP through oxidative phosphorylation
D) Synthesize ribosomal RNA
ANSWER: B
Rationale A: Incorrect. DNA replication occurs in the nucleoid and is mediated by DNA
polymerase, not the cell wall.
Rationale B: Correct. The peptidoglycan layer provides structural integrity, preventing the
cell from bursting in hypotonic environments.
Rationale C: Incorrect. ATP synthesis occurs at the plasma membrane in prokaryotes via
the electron transport chain.
Rationale D: Incorrect. rRNA is synthesized in the cytoplasm by RNA polymerase.
Question 2
Gram-positive bacteria are characterized by which of the following features?
A) Thin peptidoglycan layer and outer membrane
B) Thick peptidoglycan layer and teichoic acids
C) Presence of lipopolysaccharide in the inner membrane
D) Absence of a plasma membrane
ANSWER: B
Rationale A: Incorrect. This describes the structure of Gram-negative bacteria.
,Rationale B: Correct. Gram-positive bacteria possess a thick, multi-layered peptidoglycan
wall interwoven with teichoic and lipoteichoic acids.
Rationale C: Incorrect. Lipopolysaccharide (LPS) is found exclusively in the outer
membrane of Gram-negative bacteria.
Rationale D: Incorrect. All living bacterial cells possess an inner plasma (cytoplasmic)
membrane.
Question 3
Which structure is essential for bacterial conjugation?
A) Flagellum
B) Capsule
C) Sex pilus
D) Endospore
ANSWER: C
Rationale A: Incorrect. Flagella are primarily responsible for cellular motility.
Rationale B: Incorrect. Capsules protect against phagocytosis and desiccation, not genetic
exchange.
Rationale C: Correct. The sex pilus (F pilus) mediates the initial contact and retraction to
bring donor and recipient cells together.
Rationale D: Incorrect. Endospores are dormant survival structures, not involved in active
DNA transfer.
Question 4
Endotoxins are associated with which component of bacteria?
A) Peptidoglycan
B) Teichoic acid
C) Lipopolysaccharide (LPS)
D) Exotoxin proteins
ANSWER: C
,Rationale A: Incorrect. Peptidoglycan can trigger inflammation but is not classified as an
endotoxin.
Rationale B: Incorrect. Teichoic acids are Gram-positive wall components and are not
endotoxins.
Rationale C: Correct. Lipid A, the toxic component of LPS in the Gram-negative outer
membrane, is the classic endotoxin.
Rationale D: Incorrect. Exotoxins are secreted proteins, distinct from structural endotoxins.
Question 5
What is the role of the enzyme lysozyme in host defense?
A) Degrades bacterial DNA
B) Hydrolyzes peptidoglycan in bacterial cell walls
C) Inhibits protein synthesis
D) Disrupts the outer membrane of Gram-negative bacteria
ANSWER: B
Rationale A: Incorrect. Nucleases degrade DNA, not lysozyme.
Rationale B: Correct. Lysozyme cleaves the β-1,4-glycosidic bonds between NAM and NAG
in peptidoglycan.
Rationale C: Incorrect. Lysozyme does not target ribosomes or protein synthesis machinery.
Rationale D: Incorrect. While it affects the underlying wall, it does not primarily disrupt the
LPS outer membrane.
Question 6
Which of the following bacteria is an obligate intracellular pathogen?
A) Escherichia coli
B) Staphylococcus aureus
C) Chlamydia trachomatis
D) Bacillus subtilis
ANSWER: C
, Rationale A: Incorrect. E. coli is a facultative anaerobe that grows easily on artificial media.
Rationale B: Incorrect. S. aureus is a free-living facultative anaerobe.
Rationale C: Correct. C. trachomatis cannot synthesize its own ATP and relies entirely on
host cell machinery.
Rationale D: Incorrect. B. subtilis is a common, free-living soil bacterium.
Question 7
The process by which bacteria take up free naked DNA from the environment is called:
A) Transduction
B) Conjugation
C) Transformation
D) Transposition
ANSWER: C
Rationale A: Incorrect. Transduction involves the transfer of bacterial DNA via a
bacteriophage vector.
Rationale B: Incorrect. Conjugation requires direct cell-to-cell contact via a pilus.
Rationale C: Correct. Transformation is the uptake of free environmental DNA by a
competent cell.
Rationale D: Incorrect. Transposition refers to the movement of "jumping genes" within a
genome.
Question 8
Which of the following is NOT a characteristic of archaea?
A) Ether-linked membrane lipids
B) Presence of peptidoglycan in cell walls
C) Ability to thrive in extreme environments
D) Distinct RNA polymerase more similar to eukaryotes
ANSWER: B
