BIO 242 Microbiology Exam 2 V2
1. Which of the following bacterial cellular structures primary function is to prevent
osmotic lysis in hypotonic environments?
A. Glycocalyx
B. Cell membrane
C. Peptidoglycan cell wall
D. Endospore
E. Axial filament
Correct Answer: C. Peptidoglycan cell wall
Rationale: The rigid peptidoglycan cell wall provides structural integrity and counteracts
turgor pressure, preventing bacterial cells from swelling and undergoing osmotic lysis in
hypotonic solutions.
2. Select all features that apply to Gram-negative bacterial cell walls:
A. Thick multilayered peptidoglycan
B. Presence of Lipopolysaccharide (LPS) in the outer membrane
C. Periplasmic space containing hydrolytic enzymes
D. Teichoic and lipoteichoic acids embedded in the cell wall
E. Porin proteins facilitating solute transport
Correct Answer: B, C, E
Rationale: Gram-negative bacteria possess a thin peptidoglycan layer surrounded by an
outer membrane containing Lipopolysaccharide (LPS) and porin channels, as well as a
prominent periplasmic space. Teichoic acids and thick peptidoglycan layers are exclusive to
Gram-positive bacteria.
3. During which phase of the bacterial growth curve do cells undergo maximal binary
fission and exhibit uniform metabolic activity?
A. Death phase
B. Stationary phase
C. Lag phase
D. Log (exponential) phase
E. Long-term decline phase
Correct Answer: D. Log (exponential) phase
Rationale: The log (exponential) phase is characterized by rapid, exponential cellular
division via binary fission. Cells are most metabolically active and sensitive to antimicrobial
, agents like beta-lactam antibiotics during this phase.
4. Which specific component of the Lipopolysaccharide (LPS) molecule functions as the
toxic moiety responsible for triggering septic shock?
A. Lipid A
B. Core polysaccharide
C. O-antigen
D. N-acetylmuramic acid
E. Braun's lipoprotein
Correct Answer: A. Lipid A
Rationale: Lipid A serves as the endotoxin in Gram-negative bacteria. Upon cell lysis or
disruption, Lipid A triggers systemic inflammatory responses, fever, vasodilation, and
potentially septic shock.
5. An obligate anaerobe lacks which critical enzymes needed to neutralize toxic reactive
oxygen species (ROS)?
A. DNA polymerase and RNA polymerase
B. Superoxide dismutase (SOD) and Catalase
C. Hexokinase and Pyruvate kinase
D. Lysozyme and Transpeptidase
E. Beta-galactosidase and Permease
Correct Answer: B. Superoxide dismutase (SOD) and Catalase
Rationale: Obligate anaerobes lack superoxide dismutase (SOD) and catalase/peroxidase,
leaving them unable to detoxify superoxide radicals ($O_2^-$) and hydrogen peroxide
($H_2O_2$) formed in the presence of oxygen.
6. What metabolic pathway yields a net total of 2 ATP, 2 NADH, and 2 pyruvate molecules
from one molecule of glucose via substrate-level phosphorylation under anaerobic
conditions?
A. Krebs cycle
B. Electron transport chain
C. Pentose phosphate pathway
D. Glycolysis (Embden-Meyerhof-Parnas pathway)
E. Entner-Doudoroff pathway
Correct Answer: D. Glycolysis (Embden-Meyerhof-Parnas pathway)
Rationale: Glycolysis breaks down 1 glucose molecule into 2 pyruvate molecules,
producing a net gain of 2 ATP and 2 NADH without requiring molecular oxygen.
, 7. Which type of gene transfer mechanism involves the uptake of naked, extracellular
DNA by a competent bacterial recipient cell?
A. Conjugation
B. Specialized transduction
C. Generalized transduction
D. Transformation
E. Transposition
Correct Answer: D. Transformation
Rationale: Transformation occurs when a naturally or artificially competent bacterium
imports soluble exogenous naked DNA fragments from its environment into its cytoplasm.
8. A patient presents with a severe wound infection. Lab culture yields Gram-positive,
catalase-positive, coagulase-positive cocci in clusters. Which organism is the causative
agent?
A. Streptococcus pyogenes
B. Staphylococcus epidermidis
C. Enterococcus faecalis
D. Staphylococcus aureus
E. Streptococcus pneumoniae
Correct Answer: D. Staphylococcus aureus
Rationale: Staphylococcus aureus is characteristically Gram-positive cocci in clusters,
catalase-positive, and distinctively coagulase-positive (which differentiates it from
coagulase-negative staphylococci such as S. epidermidis).
9. Select all mechanisms that bacteria utilize to develop resistance against beta-lactam
antibiotics:
A. Production of beta-lactamase enzymes
B. Alteration of Penicillin-Binding Proteins (PBPs)
C. Expression of efflux pumps
D. Downregulation or mutation of outer membrane porins
E. Synthesis of thick poly-D-glutamic acid capsules
Correct Answer: A, B, C, D
Rationale: Resistance to beta-lactams occurs through enzyme inactivation (beta-
lactamases), target modification (mutated PBPs like PBP2a in MRSA), efflux pumps pushing
the drug out, and porin mutations reducing drug entry. Capsule synthesis aids immune
evasion but does not directly hydrolyze or block beta-lactam action.
10. What is the primary function of bacterial endospores produced by genera like
1. Which of the following bacterial cellular structures primary function is to prevent
osmotic lysis in hypotonic environments?
A. Glycocalyx
B. Cell membrane
C. Peptidoglycan cell wall
D. Endospore
E. Axial filament
Correct Answer: C. Peptidoglycan cell wall
Rationale: The rigid peptidoglycan cell wall provides structural integrity and counteracts
turgor pressure, preventing bacterial cells from swelling and undergoing osmotic lysis in
hypotonic solutions.
2. Select all features that apply to Gram-negative bacterial cell walls:
A. Thick multilayered peptidoglycan
B. Presence of Lipopolysaccharide (LPS) in the outer membrane
C. Periplasmic space containing hydrolytic enzymes
D. Teichoic and lipoteichoic acids embedded in the cell wall
E. Porin proteins facilitating solute transport
Correct Answer: B, C, E
Rationale: Gram-negative bacteria possess a thin peptidoglycan layer surrounded by an
outer membrane containing Lipopolysaccharide (LPS) and porin channels, as well as a
prominent periplasmic space. Teichoic acids and thick peptidoglycan layers are exclusive to
Gram-positive bacteria.
3. During which phase of the bacterial growth curve do cells undergo maximal binary
fission and exhibit uniform metabolic activity?
A. Death phase
B. Stationary phase
C. Lag phase
D. Log (exponential) phase
E. Long-term decline phase
Correct Answer: D. Log (exponential) phase
Rationale: The log (exponential) phase is characterized by rapid, exponential cellular
division via binary fission. Cells are most metabolically active and sensitive to antimicrobial
, agents like beta-lactam antibiotics during this phase.
4. Which specific component of the Lipopolysaccharide (LPS) molecule functions as the
toxic moiety responsible for triggering septic shock?
A. Lipid A
B. Core polysaccharide
C. O-antigen
D. N-acetylmuramic acid
E. Braun's lipoprotein
Correct Answer: A. Lipid A
Rationale: Lipid A serves as the endotoxin in Gram-negative bacteria. Upon cell lysis or
disruption, Lipid A triggers systemic inflammatory responses, fever, vasodilation, and
potentially septic shock.
5. An obligate anaerobe lacks which critical enzymes needed to neutralize toxic reactive
oxygen species (ROS)?
A. DNA polymerase and RNA polymerase
B. Superoxide dismutase (SOD) and Catalase
C. Hexokinase and Pyruvate kinase
D. Lysozyme and Transpeptidase
E. Beta-galactosidase and Permease
Correct Answer: B. Superoxide dismutase (SOD) and Catalase
Rationale: Obligate anaerobes lack superoxide dismutase (SOD) and catalase/peroxidase,
leaving them unable to detoxify superoxide radicals ($O_2^-$) and hydrogen peroxide
($H_2O_2$) formed in the presence of oxygen.
6. What metabolic pathway yields a net total of 2 ATP, 2 NADH, and 2 pyruvate molecules
from one molecule of glucose via substrate-level phosphorylation under anaerobic
conditions?
A. Krebs cycle
B. Electron transport chain
C. Pentose phosphate pathway
D. Glycolysis (Embden-Meyerhof-Parnas pathway)
E. Entner-Doudoroff pathway
Correct Answer: D. Glycolysis (Embden-Meyerhof-Parnas pathway)
Rationale: Glycolysis breaks down 1 glucose molecule into 2 pyruvate molecules,
producing a net gain of 2 ATP and 2 NADH without requiring molecular oxygen.
, 7. Which type of gene transfer mechanism involves the uptake of naked, extracellular
DNA by a competent bacterial recipient cell?
A. Conjugation
B. Specialized transduction
C. Generalized transduction
D. Transformation
E. Transposition
Correct Answer: D. Transformation
Rationale: Transformation occurs when a naturally or artificially competent bacterium
imports soluble exogenous naked DNA fragments from its environment into its cytoplasm.
8. A patient presents with a severe wound infection. Lab culture yields Gram-positive,
catalase-positive, coagulase-positive cocci in clusters. Which organism is the causative
agent?
A. Streptococcus pyogenes
B. Staphylococcus epidermidis
C. Enterococcus faecalis
D. Staphylococcus aureus
E. Streptococcus pneumoniae
Correct Answer: D. Staphylococcus aureus
Rationale: Staphylococcus aureus is characteristically Gram-positive cocci in clusters,
catalase-positive, and distinctively coagulase-positive (which differentiates it from
coagulase-negative staphylococci such as S. epidermidis).
9. Select all mechanisms that bacteria utilize to develop resistance against beta-lactam
antibiotics:
A. Production of beta-lactamase enzymes
B. Alteration of Penicillin-Binding Proteins (PBPs)
C. Expression of efflux pumps
D. Downregulation or mutation of outer membrane porins
E. Synthesis of thick poly-D-glutamic acid capsules
Correct Answer: A, B, C, D
Rationale: Resistance to beta-lactams occurs through enzyme inactivation (beta-
lactamases), target modification (mutated PBPs like PBP2a in MRSA), efflux pumps pushing
the drug out, and porin mutations reducing drug entry. Capsule synthesis aids immune
evasion but does not directly hydrolyze or block beta-lactam action.
10. What is the primary function of bacterial endospores produced by genera like
