MICROBIOLOGY BIOL 271 EXAM STUDY GUIDE WITH
QUESTIONS AND WELL EXPOUNDED ANSWERS
1. Which of the following best describes the primary difference between archaea
and bacteria in terms of cell wall composition?
A. Archaea contain peptidoglycan while bacteria do not
B. Bacteria contain peptidoglycan while archaea do not
C. Both contain identical peptidoglycan structures
D. Neither contains any cell wall components
Correct Answer: B
Explanation: Bacteria have peptidoglycan in their cell walls, while archaea lack
peptidoglycan and instead have pseudopeptidoglycan or other polysaccharides.
This is a fundamental distinguishing feature between the two domains.
2. A patient presents with fever, chills, and a rash that spreads centrifugally from
the trunk to extremities. Gram staining reveals small, gram-negative coccobacilli.
Which microbial virulence factor is most likely responsible for the intracellular
survival of this pathogen?
A. Capsule preventing phagocytosis
B. Type III secretion system injecting effector proteins
C. Endotoxin triggering cytokine release
D. Exotoxin disrupting protein synthesis
Correct Answer: B
Explanation: The Type III secretion system allows intracellular pathogens like
Rickettsia to inject effector proteins into host cells, enabling survival and
replication inside host cells. This is characteristic of many gram-negative
intracellular bacteria.
3. In microbial metabolism, which electron transport chain component is unique to
aerobic respiration in bacteria?
A. NADH dehydrogenase
B. Cytochrome c oxidase
C. Ubiquinone
D. Succinate dehydrogenase
Correct Answer: B
Explanation: Cytochrome c oxidase (Complex IV) is the terminal electron
acceptor in aerobic respiration, transferring electrons to oxygen. Anaerobic
respiration uses different terminal acceptors and lacks this specific enzyme.
,4. Which mechanism best explains how bacteria develop resistance to beta-lactam
antibiotics?
A. Mutation in ribosomal RNA genes
B. Production of beta-lactamase enzymes that hydrolyze the beta-lactam ring
C. Decreased membrane permeability to the drug
D. Active efflux pumps removing the antibiotic
Correct Answer: B
Explanation: Beta-lactamases are enzymes that cleave the beta-lactam ring,
rendering penicillins, cephalosporins, and related antibiotics ineffective. This is
the most common mechanism of beta-lactam resistance.
5. During bacterial conjugation, what is the primary function of the F plasmid?
A. Encoding antibiotic resistance genes
B. Producing the sex pilus for DNA transfer
C. Regulating bacterial metabolism
D. Synthesizing viral capsid proteins
Correct Answer: B
Explanation: The F (fertility) plasmid contains genes for sex pilus formation,
which facilitates direct cell-to-cell contact and DNA transfer during
conjugation. This is a key mechanism of horizontal gene transfer.
6. A microbiologist is culturing an unknown organism. The organism grows
optimally at 37°C, requires oxygen, and produces catalase and coagulase
enzymes. Which genus is most likely?
A. Streptococcus
B. Staphylococcus
C. Escherichia
D. Pseudomonas
Correct Answer: B
Explanation: Staphylococcus aureus is catalase-positive, coagulase-positive,
facultatively anaerobic (grows with oxygen), and optimal at 37°C.
Streptococcus is catalase-negative, and Escherichia/Pseudomonas don't
produce coagulase.
7. Which immune response component is primarily responsible for neutralizing
viral particles before they enter host cells?
A. Cytotoxic T lymphocytes
B. Helper T cells
C. Neutralizing antibodies (IgG/IgM)
D. Natural killer cells
, Correct Answer: C
Explanation: Neutralizing antibodies bind to viral surface proteins, preventing
attachment and entry into host cells. This is the primary defense against viral
infection before cell entry occurs.
8. In the Lac operon of E. coli, what happens when both glucose and lactose are
present?
A. High transcription due to CAP binding and lactose induction
B. Low transcription due to catabolite repression despite lactose presence
C. No transcription because the repressor is active
D. Maximum transcription because both sugars are available
Correct Answer: B
Explanation: When glucose is present, cAMP levels are low, preventing CAP
binding. Even though lactose inactivates the repressor, low CAP binding results
in low transcription (catabolite repression).
9. Which sterilization method is most appropriate for heat-sensitive plastic
laboratory equipment?
A. Autoclaving at 121°C for 15 minutes
B. Dry heat at 160°C for 2 hours
C. Ethylene oxide gas exposure
D. Boiling water for 30 minutes
Correct Answer: C
Explanation: Ethylene oxide gas sterilizes at low temperatures (37-60°C),
making it ideal for heat-sensitive materials like plastics. Autoclaving and dry
heat would melt or damage plastic equipment.
10. A patient with HIV has a CD4+ T cell count of 150 cells/mm³. Which
opportunistic infection is most likely to occur at this immunosuppression level?
A. Streptococcus pneumoniae pneumonia
B. Toxoplasma gondii encephalitis
C. Influenza virus infection
D. Staphylococcus aureus skin infection
Correct Answer: B
Explanation: CD4+ counts below 200 cells/mm³ indicate severe
immunosuppression, making patients susceptible to opportunistic infections like
Toxoplasma gondii, Pneumocystis jirovecii, and Mycobacterium avium
complex.
QUESTIONS AND WELL EXPOUNDED ANSWERS
1. Which of the following best describes the primary difference between archaea
and bacteria in terms of cell wall composition?
A. Archaea contain peptidoglycan while bacteria do not
B. Bacteria contain peptidoglycan while archaea do not
C. Both contain identical peptidoglycan structures
D. Neither contains any cell wall components
Correct Answer: B
Explanation: Bacteria have peptidoglycan in their cell walls, while archaea lack
peptidoglycan and instead have pseudopeptidoglycan or other polysaccharides.
This is a fundamental distinguishing feature between the two domains.
2. A patient presents with fever, chills, and a rash that spreads centrifugally from
the trunk to extremities. Gram staining reveals small, gram-negative coccobacilli.
Which microbial virulence factor is most likely responsible for the intracellular
survival of this pathogen?
A. Capsule preventing phagocytosis
B. Type III secretion system injecting effector proteins
C. Endotoxin triggering cytokine release
D. Exotoxin disrupting protein synthesis
Correct Answer: B
Explanation: The Type III secretion system allows intracellular pathogens like
Rickettsia to inject effector proteins into host cells, enabling survival and
replication inside host cells. This is characteristic of many gram-negative
intracellular bacteria.
3. In microbial metabolism, which electron transport chain component is unique to
aerobic respiration in bacteria?
A. NADH dehydrogenase
B. Cytochrome c oxidase
C. Ubiquinone
D. Succinate dehydrogenase
Correct Answer: B
Explanation: Cytochrome c oxidase (Complex IV) is the terminal electron
acceptor in aerobic respiration, transferring electrons to oxygen. Anaerobic
respiration uses different terminal acceptors and lacks this specific enzyme.
,4. Which mechanism best explains how bacteria develop resistance to beta-lactam
antibiotics?
A. Mutation in ribosomal RNA genes
B. Production of beta-lactamase enzymes that hydrolyze the beta-lactam ring
C. Decreased membrane permeability to the drug
D. Active efflux pumps removing the antibiotic
Correct Answer: B
Explanation: Beta-lactamases are enzymes that cleave the beta-lactam ring,
rendering penicillins, cephalosporins, and related antibiotics ineffective. This is
the most common mechanism of beta-lactam resistance.
5. During bacterial conjugation, what is the primary function of the F plasmid?
A. Encoding antibiotic resistance genes
B. Producing the sex pilus for DNA transfer
C. Regulating bacterial metabolism
D. Synthesizing viral capsid proteins
Correct Answer: B
Explanation: The F (fertility) plasmid contains genes for sex pilus formation,
which facilitates direct cell-to-cell contact and DNA transfer during
conjugation. This is a key mechanism of horizontal gene transfer.
6. A microbiologist is culturing an unknown organism. The organism grows
optimally at 37°C, requires oxygen, and produces catalase and coagulase
enzymes. Which genus is most likely?
A. Streptococcus
B. Staphylococcus
C. Escherichia
D. Pseudomonas
Correct Answer: B
Explanation: Staphylococcus aureus is catalase-positive, coagulase-positive,
facultatively anaerobic (grows with oxygen), and optimal at 37°C.
Streptococcus is catalase-negative, and Escherichia/Pseudomonas don't
produce coagulase.
7. Which immune response component is primarily responsible for neutralizing
viral particles before they enter host cells?
A. Cytotoxic T lymphocytes
B. Helper T cells
C. Neutralizing antibodies (IgG/IgM)
D. Natural killer cells
, Correct Answer: C
Explanation: Neutralizing antibodies bind to viral surface proteins, preventing
attachment and entry into host cells. This is the primary defense against viral
infection before cell entry occurs.
8. In the Lac operon of E. coli, what happens when both glucose and lactose are
present?
A. High transcription due to CAP binding and lactose induction
B. Low transcription due to catabolite repression despite lactose presence
C. No transcription because the repressor is active
D. Maximum transcription because both sugars are available
Correct Answer: B
Explanation: When glucose is present, cAMP levels are low, preventing CAP
binding. Even though lactose inactivates the repressor, low CAP binding results
in low transcription (catabolite repression).
9. Which sterilization method is most appropriate for heat-sensitive plastic
laboratory equipment?
A. Autoclaving at 121°C for 15 minutes
B. Dry heat at 160°C for 2 hours
C. Ethylene oxide gas exposure
D. Boiling water for 30 minutes
Correct Answer: C
Explanation: Ethylene oxide gas sterilizes at low temperatures (37-60°C),
making it ideal for heat-sensitive materials like plastics. Autoclaving and dry
heat would melt or damage plastic equipment.
10. A patient with HIV has a CD4+ T cell count of 150 cells/mm³. Which
opportunistic infection is most likely to occur at this immunosuppression level?
A. Streptococcus pneumoniae pneumonia
B. Toxoplasma gondii encephalitis
C. Influenza virus infection
D. Staphylococcus aureus skin infection
Correct Answer: B
Explanation: CD4+ counts below 200 cells/mm³ indicate severe
immunosuppression, making patients susceptible to opportunistic infections like
Toxoplasma gondii, Pneumocystis jirovecii, and Mycobacterium avium
complex.
