Microbiology BIO 420 Final Practice Exam Test Bank B with
Correctly Answered Questions with Rationales/ BMCC Bio 420
Latest Final Practice Test - 140 Questions
Section 1: Microbial Cell Structure and Function (Questions 1-15)
1 A research team isolates a novel bacterium from a deep-sea hydrothermal vent. The isolate grows optimally at
85°C and pH 5.0. Upon analysis, its cell wall contains pseudopeptidoglycan and its membrane lipids are
composed of isoprenoid chains ether-linked to glycerol. In which domain should this organism be classified?
A) Bacteria, due to the presence of a cell wall
B) Archaea, due to ether-linked lipids and pseudopeptidoglycan
C) Eukarya, due to growth at low pH
D) Bacteria, due to the optimal growth temperature above 80°C
Answer: B
Rationale: Archaea are characterized by ether-linked isoprenoid lipids in their membranes and pseudopeptidoglycan
in their cell walls, distinguishing them from Bacteria (which have ester-linked fatty acids and peptidoglycan).
Extreme thermophiles and acidophiles are commonly Archaea.
2 In a Gram-negative bacterium, a mutation in the lpxC gene results in the accumulation of a precursor that cannot
be converted to lipid A. What is the most likely consequence for the outer membrane?
A) Increased permeability to hydrophobic antibiotics
B) Enhanced stability due to increased cross-linking
C) Loss of barrier function and increased sensitivity to detergents
D) Thickening of the peptidoglycan layer
Answer: C
Rationale: Lipid A is a core component of lipopolysaccharide (LPS), which forms the outer leaflet of the outer
membrane in Gram-negative bacteria. LPS provides a permeability barrier against hydrophobic molecules and
detergents. Loss of lipid A disrupts the outer membrane integrity, increasing sensitivity to detergents and
hydrophobic antibiotics.
3 During a study of bacterial motility, you observe that a strain of Escherichia coli exhibits a smooth swimming
pattern with occasional reversals. Which of the following best explains the molecular mechanism underlying
these reversals?
A) Counterclockwise rotation of flagella causes tumbling; clockwise rotation causes smooth swimming
B) Clockwise rotation of flagella causes smooth swimming; counterclockwise rotation causes tumbling
C) Smooth swimming occurs when all flagella rotate counterclockwise; reversals occur when some flagella
rotate clockwise
D) Smooth swimming occurs when flagella rotate clockwise; reversals occur when the motor direction changes
randomly
Answer: C
Rationale: In peritrichously flagellated bacteria like E. coli, counterclockwise rotation of all flagella causes them to
form a bundle and propel the cell smoothly (run). Reversals (tumbles) occur when one or more flagella switch to
clockwise rotation, disrupting the bundle and causing random reorientation.
,4 A microbiologist is studying a bacterium that produces a capsule composed of poly-D-glutamic acid. Which of
the following is a direct functional advantage of this capsule?
A) It provides structural rigidity to the cell wall
B) It facilitates attachment to host tissues via pili
C) It resists phagocytosis by inhibiting complement activation
D) It stores nutrients for use during starvation
Answer: C
Rationale: Capsules are antiphagocytic; they impair opsonization and complement activation, preventing engulfment
by immune cells. Poly-D-glutamic acid capsules, found in Bacillus anthracis, are particularly effective at evading
the immune response. They do not provide structural rigidity (that is the cell wall's role) nor do they directly
facilitate attachment (pili do that) or store nutrients.
5 In an experiment, you treat a bacterial culture with an inhibitor that specifically blocks the function of FtsZ.
What immediate effect would you observe?
A) Inhibition of protein synthesis
B) Arrest of DNA replication
C) Failure of cell division, leading to filamentous growth
D) Disruption of the cell membrane potential
Answer: C
Rationale: FtsZ is a tubulin homolog that forms the Z-ring at the division septum, essential for cytokinesis in
bacteria. Inhibiting FtsZ prevents Z-ring formation, blocking cell division. Cells continue to grow but cannot
divide, resulting in elongated filaments. FtsZ does not directly affect protein synthesis, DNA replication, or
membrane potential.
6 A clinical isolate of Streptococcus pneumoniae is found to have a mutation in the gene encoding sortase A
(srtA). Which phenotype would most likely be associated with this mutation?
A) Increased ability to form biofilms
B) Reduced adherence to host epithelial cells
C) Enhanced resistance to beta-lactam antibiotics
D) Loss of capsule production
Answer: B
Rationale: Sortase A is an enzyme that covalently attaches surface proteins (e.g., adhesins) to the peptidoglycan of
Gram-positive bacteria. Without sortase A, these proteins are not anchored, leading to reduced adherence. Biofilm
formation is often mediated by different factors, beta-lactam resistance is primarily via penicillin-binding proteins,
and capsule production involves separate pathways.
7 A researcher is comparing the cell walls of a Gram-positive bacterium (Bacillus subtilis) and a Gram-negative
bacterium (Escherichia coli). Which of the following correctly describes a difference in the chemical
composition of their cell walls?
A) Both contain teichoic acids, but only Gram-negative bacteria have lipopolysaccharide
B) Gram-positive bacteria have a thinner peptidoglycan layer with higher cross-linking
C) Gram-negative bacteria have an outer membrane containing lipopolysaccharide and porins
D) Both contain N-acetylmuramic acid and N-acetylglucosamine, but only Gram-positive bacteria have D-amino
acids in the peptide cross-links
Answer: C
Rationale: Gram-negative bacteria have an outer membrane with lipopolysaccharide (LPS) and porins.
Gram-positive bacteria lack an outer membrane but have a thick peptidoglycan layer with teichoic acids; they do
,not have LPS. Both contain NAM and NAG, and both use D-amino acids in peptide cross-links. The peptidoglycan
layer in Gram-positive bacteria is thicker, not thinner.
8 Which of the following experimental observations would provide the strongest evidence that a bacterial
structure is an endospore rather than a vegetative cell?
A) The structure is stained with malachite green and resists decolorization
B) The structure is metabolically active and divides rapidly
C) The structure contains a high concentration of dipicolinic acid and calcium ions
D) Both A and C
Answer: D
Rationale: Endospores are characterized by the presence of dipicolinic acid (DPA) complexed with calcium ions,
which contributes to heat resistance. The malachite green staining method is specific for endospores because the
dye penetrates the spore coat and is retained after decolorization. Vegetative cells are metabolically active and do
not contain high levels of DPA.
9 A marine bacterium possesses a flagellum that is enclosed within the periplasmic space and rotates to generate
motility. This flagellar arrangement is most characteristic of which group?
A) Spirochetes, where the flagellum is called an axial filament
B) Pseudomonads, with polar flagella
C) Enteric bacteria, with peritrichous flagella
D) Myxobacteria, with gliding motility
Answer: A
Rationale: Spirochetes have periplasmic flagella (axial filaments) that run between the outer membrane and the cell
cylinder. Rotation of these flagella causes the cell to corkscrew through viscous environments. Pseudomonads have
polar flagella that extend externally, enteric bacteria have peritrichous flagella, and myxobacteria glide without
flagella.
10 A biochemist isolates a membrane fraction from a halophilic archaeon and analyzes its lipid composition.
Which of the following lipids would be expected to be most abundant?
A) Glycerophospholipids with ester-linked fatty acids
B) Sphingolipids with amide-linked fatty acids
C) Glycerol diethers with isoprenoid chains
D) Bilayer-forming bolaamphiphiles with two polar heads
Answer: C
Rationale: Archaea, including halophiles, have membrane lipids composed of glycerol diethers (archaeol) or
glycerol tetraethers (caldarchaeol) with isoprenoid chains ether-linked to glycerol. These lipids can form
monolayers or bilayers. Ester-linked fatty acids are typical of Bacteria and Eukarya, not Archaea. Sphingolipids are
found in eukaryotes. Bolaamphiphiles with two polar heads are typical of some archaeal tetraether lipids but are not
the most abundant in halophiles.
11 A researcher isolates a novel bacterium from a deep-sea hydrothermal vent. The organism lacks peptidoglycan
in its cell wall, has membrane lipids composed of ether-linked isoprenoids, and its ribosomes are sensitive to
diphtheria toxin. Which of the following best describes the cell envelope structure of this organism?
A) A single lipid bilayer with an outer membrane containing lipopolysaccharide
B) A pseudopeptidoglycan layer surrounded by a lipid bilayer
C) A cytoplasmic membrane with an S-layer and no outer membrane
D) A thick peptidoglycan layer with teichoic acids
, Answer: C
Rationale: The organism is an archaeon (ether-linked lipids, no peptidoglycan, diphtheria toxin sensitivity due to
ADP-ribosylation of EF-2, which is present in archaea and eukaryotes). Many archaea have a cytoplasmic
membrane and an S-layer as the outermost cell wall component, lacking an outer membrane. Option A (LPS outer
membrane) is characteristic of Gram-negative bacteria; B (pseudopeptidoglycan) occurs in some archaea but is not
universal and implies a thick layer; D describes Gram-positive bacteria.
12 In a laboratory experiment, a Gram-negative bacterium is treated with a sublethal concentration of a cationic
antimicrobial peptide (CAMP). The treatment causes increased permeability of the outer membrane but does
not immediately lyse the cell. Which of the following structural modifications is most likely responsible for the
initial survival of the bacterium?
A) Upregulation of lipopolysaccharide (LPS) O-antigen chain length
B) Increased expression of Braun's lipoprotein (Lpp)
C) Activation of the Rcs phosphorelay system to thicken the peptidoglycan layer
D) Incorporation of lysyl-phosphatidylglycerol into the inner membrane
Answer: A
Rationale: CAMPs often target the outer membrane by interacting with LPS. Increasing O-antigen length can reduce
CAMP binding by steric hindrance or charge masking, thereby reducing outer membrane permeabilization. Option
B (Lpp) anchors the outer membrane to peptidoglycan but does not directly affect CAMP binding; C
(peptidoglycan thickening) is more typical of Gram-positive responses; D (lysyl-PG) modifies inner membrane
charge but does not protect the outer membrane.
13 A researcher is studying the export of a hemolysin toxin from a uropathogenic Escherichia coli strain. The
toxin is synthesized in the cytoplasm and must be transported across both the inner and outer membranes
without a periplasmic intermediate. Which secretion system is most likely responsible for this process?
A) Type II secretion system (T2SS)
B) Type III secretion system (T3SS)
C) Type V secretion system (autotransporter)
D) Type I secretion system (T1SS)
Answer: D
Rationale: Type I secretion systems (e.g., for hemolysin A) transport proteins directly from the cytoplasm to the
extracellular space without a periplasmic intermediate, using an ABC transporter, a membrane fusion protein, and
an outer membrane porin. T2SS involves a periplasmic intermediate; T3SS delivers proteins directly into host cells
but still involves a needle complex; T5SS (autotransporters) also have a periplasmic intermediate and require the
Sec machinery for inner membrane translocation.
14 A clinical microbiologist examines a Gram-stained sputum sample and observes numerous neutrophils
containing intracellular diplococci. The organism is fastidious, requires enriched media, and is
oxidase-positive. Which of the following cell surface structures is the primary virulence factor that enables this
organism to evade phagocytosis by neutrophils?
A) Lipooligosaccharide (LOS) with sialic acid caps
B) Polysaccharide capsule
C) Type IV pili
D) Porin proteins (PorA and PorB)
Answer: B
Rationale: The description matches Neisseria meningitidis (or N. gonorrhoeae), which have a polysaccharide
capsule (N. meningitidis) that inhibits phagocytosis. N. gonorrhoeae lacks a capsule but uses other mechanisms.
Correctly Answered Questions with Rationales/ BMCC Bio 420
Latest Final Practice Test - 140 Questions
Section 1: Microbial Cell Structure and Function (Questions 1-15)
1 A research team isolates a novel bacterium from a deep-sea hydrothermal vent. The isolate grows optimally at
85°C and pH 5.0. Upon analysis, its cell wall contains pseudopeptidoglycan and its membrane lipids are
composed of isoprenoid chains ether-linked to glycerol. In which domain should this organism be classified?
A) Bacteria, due to the presence of a cell wall
B) Archaea, due to ether-linked lipids and pseudopeptidoglycan
C) Eukarya, due to growth at low pH
D) Bacteria, due to the optimal growth temperature above 80°C
Answer: B
Rationale: Archaea are characterized by ether-linked isoprenoid lipids in their membranes and pseudopeptidoglycan
in their cell walls, distinguishing them from Bacteria (which have ester-linked fatty acids and peptidoglycan).
Extreme thermophiles and acidophiles are commonly Archaea.
2 In a Gram-negative bacterium, a mutation in the lpxC gene results in the accumulation of a precursor that cannot
be converted to lipid A. What is the most likely consequence for the outer membrane?
A) Increased permeability to hydrophobic antibiotics
B) Enhanced stability due to increased cross-linking
C) Loss of barrier function and increased sensitivity to detergents
D) Thickening of the peptidoglycan layer
Answer: C
Rationale: Lipid A is a core component of lipopolysaccharide (LPS), which forms the outer leaflet of the outer
membrane in Gram-negative bacteria. LPS provides a permeability barrier against hydrophobic molecules and
detergents. Loss of lipid A disrupts the outer membrane integrity, increasing sensitivity to detergents and
hydrophobic antibiotics.
3 During a study of bacterial motility, you observe that a strain of Escherichia coli exhibits a smooth swimming
pattern with occasional reversals. Which of the following best explains the molecular mechanism underlying
these reversals?
A) Counterclockwise rotation of flagella causes tumbling; clockwise rotation causes smooth swimming
B) Clockwise rotation of flagella causes smooth swimming; counterclockwise rotation causes tumbling
C) Smooth swimming occurs when all flagella rotate counterclockwise; reversals occur when some flagella
rotate clockwise
D) Smooth swimming occurs when flagella rotate clockwise; reversals occur when the motor direction changes
randomly
Answer: C
Rationale: In peritrichously flagellated bacteria like E. coli, counterclockwise rotation of all flagella causes them to
form a bundle and propel the cell smoothly (run). Reversals (tumbles) occur when one or more flagella switch to
clockwise rotation, disrupting the bundle and causing random reorientation.
,4 A microbiologist is studying a bacterium that produces a capsule composed of poly-D-glutamic acid. Which of
the following is a direct functional advantage of this capsule?
A) It provides structural rigidity to the cell wall
B) It facilitates attachment to host tissues via pili
C) It resists phagocytosis by inhibiting complement activation
D) It stores nutrients for use during starvation
Answer: C
Rationale: Capsules are antiphagocytic; they impair opsonization and complement activation, preventing engulfment
by immune cells. Poly-D-glutamic acid capsules, found in Bacillus anthracis, are particularly effective at evading
the immune response. They do not provide structural rigidity (that is the cell wall's role) nor do they directly
facilitate attachment (pili do that) or store nutrients.
5 In an experiment, you treat a bacterial culture with an inhibitor that specifically blocks the function of FtsZ.
What immediate effect would you observe?
A) Inhibition of protein synthesis
B) Arrest of DNA replication
C) Failure of cell division, leading to filamentous growth
D) Disruption of the cell membrane potential
Answer: C
Rationale: FtsZ is a tubulin homolog that forms the Z-ring at the division septum, essential for cytokinesis in
bacteria. Inhibiting FtsZ prevents Z-ring formation, blocking cell division. Cells continue to grow but cannot
divide, resulting in elongated filaments. FtsZ does not directly affect protein synthesis, DNA replication, or
membrane potential.
6 A clinical isolate of Streptococcus pneumoniae is found to have a mutation in the gene encoding sortase A
(srtA). Which phenotype would most likely be associated with this mutation?
A) Increased ability to form biofilms
B) Reduced adherence to host epithelial cells
C) Enhanced resistance to beta-lactam antibiotics
D) Loss of capsule production
Answer: B
Rationale: Sortase A is an enzyme that covalently attaches surface proteins (e.g., adhesins) to the peptidoglycan of
Gram-positive bacteria. Without sortase A, these proteins are not anchored, leading to reduced adherence. Biofilm
formation is often mediated by different factors, beta-lactam resistance is primarily via penicillin-binding proteins,
and capsule production involves separate pathways.
7 A researcher is comparing the cell walls of a Gram-positive bacterium (Bacillus subtilis) and a Gram-negative
bacterium (Escherichia coli). Which of the following correctly describes a difference in the chemical
composition of their cell walls?
A) Both contain teichoic acids, but only Gram-negative bacteria have lipopolysaccharide
B) Gram-positive bacteria have a thinner peptidoglycan layer with higher cross-linking
C) Gram-negative bacteria have an outer membrane containing lipopolysaccharide and porins
D) Both contain N-acetylmuramic acid and N-acetylglucosamine, but only Gram-positive bacteria have D-amino
acids in the peptide cross-links
Answer: C
Rationale: Gram-negative bacteria have an outer membrane with lipopolysaccharide (LPS) and porins.
Gram-positive bacteria lack an outer membrane but have a thick peptidoglycan layer with teichoic acids; they do
,not have LPS. Both contain NAM and NAG, and both use D-amino acids in peptide cross-links. The peptidoglycan
layer in Gram-positive bacteria is thicker, not thinner.
8 Which of the following experimental observations would provide the strongest evidence that a bacterial
structure is an endospore rather than a vegetative cell?
A) The structure is stained with malachite green and resists decolorization
B) The structure is metabolically active and divides rapidly
C) The structure contains a high concentration of dipicolinic acid and calcium ions
D) Both A and C
Answer: D
Rationale: Endospores are characterized by the presence of dipicolinic acid (DPA) complexed with calcium ions,
which contributes to heat resistance. The malachite green staining method is specific for endospores because the
dye penetrates the spore coat and is retained after decolorization. Vegetative cells are metabolically active and do
not contain high levels of DPA.
9 A marine bacterium possesses a flagellum that is enclosed within the periplasmic space and rotates to generate
motility. This flagellar arrangement is most characteristic of which group?
A) Spirochetes, where the flagellum is called an axial filament
B) Pseudomonads, with polar flagella
C) Enteric bacteria, with peritrichous flagella
D) Myxobacteria, with gliding motility
Answer: A
Rationale: Spirochetes have periplasmic flagella (axial filaments) that run between the outer membrane and the cell
cylinder. Rotation of these flagella causes the cell to corkscrew through viscous environments. Pseudomonads have
polar flagella that extend externally, enteric bacteria have peritrichous flagella, and myxobacteria glide without
flagella.
10 A biochemist isolates a membrane fraction from a halophilic archaeon and analyzes its lipid composition.
Which of the following lipids would be expected to be most abundant?
A) Glycerophospholipids with ester-linked fatty acids
B) Sphingolipids with amide-linked fatty acids
C) Glycerol diethers with isoprenoid chains
D) Bilayer-forming bolaamphiphiles with two polar heads
Answer: C
Rationale: Archaea, including halophiles, have membrane lipids composed of glycerol diethers (archaeol) or
glycerol tetraethers (caldarchaeol) with isoprenoid chains ether-linked to glycerol. These lipids can form
monolayers or bilayers. Ester-linked fatty acids are typical of Bacteria and Eukarya, not Archaea. Sphingolipids are
found in eukaryotes. Bolaamphiphiles with two polar heads are typical of some archaeal tetraether lipids but are not
the most abundant in halophiles.
11 A researcher isolates a novel bacterium from a deep-sea hydrothermal vent. The organism lacks peptidoglycan
in its cell wall, has membrane lipids composed of ether-linked isoprenoids, and its ribosomes are sensitive to
diphtheria toxin. Which of the following best describes the cell envelope structure of this organism?
A) A single lipid bilayer with an outer membrane containing lipopolysaccharide
B) A pseudopeptidoglycan layer surrounded by a lipid bilayer
C) A cytoplasmic membrane with an S-layer and no outer membrane
D) A thick peptidoglycan layer with teichoic acids
, Answer: C
Rationale: The organism is an archaeon (ether-linked lipids, no peptidoglycan, diphtheria toxin sensitivity due to
ADP-ribosylation of EF-2, which is present in archaea and eukaryotes). Many archaea have a cytoplasmic
membrane and an S-layer as the outermost cell wall component, lacking an outer membrane. Option A (LPS outer
membrane) is characteristic of Gram-negative bacteria; B (pseudopeptidoglycan) occurs in some archaea but is not
universal and implies a thick layer; D describes Gram-positive bacteria.
12 In a laboratory experiment, a Gram-negative bacterium is treated with a sublethal concentration of a cationic
antimicrobial peptide (CAMP). The treatment causes increased permeability of the outer membrane but does
not immediately lyse the cell. Which of the following structural modifications is most likely responsible for the
initial survival of the bacterium?
A) Upregulation of lipopolysaccharide (LPS) O-antigen chain length
B) Increased expression of Braun's lipoprotein (Lpp)
C) Activation of the Rcs phosphorelay system to thicken the peptidoglycan layer
D) Incorporation of lysyl-phosphatidylglycerol into the inner membrane
Answer: A
Rationale: CAMPs often target the outer membrane by interacting with LPS. Increasing O-antigen length can reduce
CAMP binding by steric hindrance or charge masking, thereby reducing outer membrane permeabilization. Option
B (Lpp) anchors the outer membrane to peptidoglycan but does not directly affect CAMP binding; C
(peptidoglycan thickening) is more typical of Gram-positive responses; D (lysyl-PG) modifies inner membrane
charge but does not protect the outer membrane.
13 A researcher is studying the export of a hemolysin toxin from a uropathogenic Escherichia coli strain. The
toxin is synthesized in the cytoplasm and must be transported across both the inner and outer membranes
without a periplasmic intermediate. Which secretion system is most likely responsible for this process?
A) Type II secretion system (T2SS)
B) Type III secretion system (T3SS)
C) Type V secretion system (autotransporter)
D) Type I secretion system (T1SS)
Answer: D
Rationale: Type I secretion systems (e.g., for hemolysin A) transport proteins directly from the cytoplasm to the
extracellular space without a periplasmic intermediate, using an ABC transporter, a membrane fusion protein, and
an outer membrane porin. T2SS involves a periplasmic intermediate; T3SS delivers proteins directly into host cells
but still involves a needle complex; T5SS (autotransporters) also have a periplasmic intermediate and require the
Sec machinery for inner membrane translocation.
14 A clinical microbiologist examines a Gram-stained sputum sample and observes numerous neutrophils
containing intracellular diplococci. The organism is fastidious, requires enriched media, and is
oxidase-positive. Which of the following cell surface structures is the primary virulence factor that enables this
organism to evade phagocytosis by neutrophils?
A) Lipooligosaccharide (LOS) with sialic acid caps
B) Polysaccharide capsule
C) Type IV pili
D) Porin proteins (PorA and PorB)
Answer: B
Rationale: The description matches Neisseria meningitidis (or N. gonorrhoeae), which have a polysaccharide
capsule (N. meningitidis) that inhibits phagocytosis. N. gonorrhoeae lacks a capsule but uses other mechanisms.
