MICROBIOLOGY BIOL 271 CASE STUDY
COMPREHENSIVE EXAM QUESTIONS
AND ANSWERS
1. A patient presents with a persistent cough and night sweats. A sputum sample is stained
using the Ziehl-Neelsen technique, revealing bright red bacilli. Which component of the cell
wall is responsible for this staining result?
A. Lipopolysaccharide
B. Mycolic acid
C. Teichoic acid
D. Peptidoglycan
Answer: B
Conceptual Explanation: Mycolic acids are waxy lipids found in the cell walls of
Mycobacterium species, which resist decolorization by acid-alcohol in the acid-fast stain.
2. In a clinical lab, a technician uses a microscope with a numerical aperture of 1.25 and a
light source of 500 nm. What is the limit of resolution for this microscope?
A. 200 nm
B. 0.2 µm
,C. 0.5 µm
D. 250 nm
Answer: B
Conceptual Explanation: Resolution (d) = wavelength λ / (2 × NA). 500 / (2 × 1.25) = 200
nm or 0.2 µm.
3. A bacterium is isolated from a deep-sea hydrothermal vent where temperatures reach
95°C. This organism is most likely a:
A. Mesophile
B. Hyperthermophile
C. Psychrotroph
D. Thermophile
Answer: B
Conceptual Explanation: Hyperthermophiles have optimal growth temperatures
generally above 80°C, often found in volcanic or hydrothermal environments.
4. During the process of aerobic respiration, which molecule serves as the final electron
acceptor?
A. Pyruvate
B. Nitrate
C. Oxygen
, D. Sulfate
Answer: C
Conceptual Explanation: In aerobic respiration, molecular oxygen (O2) is the terminal
electron acceptor at the end of the electron transport chain.
5. A strain of E. coli has a mutation in the lacI gene, resulting in a non-functional repressor
protein. What is the expected phenotype in the absence of lactose?
A. The lac operon will be constitutively expressed.
B. The lac operon will never be expressed.
C. The lac operon will only be expressed if glucose is absent.
D. The lac operon will be expressed only when cAMP levels are low.
Answer: A
Conceptual Explanation: If the repressor is non-functional, it cannot bind to the operator
to block transcription; therefore, the operon is ‘on’ even without lactose.
6. Which of the following describes a ‘F+ to F-’ bacterial conjugation?
A. Transfer of chromosomal DNA through a pilus.
B. Uptake of naked DNA from the environment.
C. Integration of a plasmid into the host chromosome.
D. Transfer of a plasmid resulting in two F+ cells.
COMPREHENSIVE EXAM QUESTIONS
AND ANSWERS
1. A patient presents with a persistent cough and night sweats. A sputum sample is stained
using the Ziehl-Neelsen technique, revealing bright red bacilli. Which component of the cell
wall is responsible for this staining result?
A. Lipopolysaccharide
B. Mycolic acid
C. Teichoic acid
D. Peptidoglycan
Answer: B
Conceptual Explanation: Mycolic acids are waxy lipids found in the cell walls of
Mycobacterium species, which resist decolorization by acid-alcohol in the acid-fast stain.
2. In a clinical lab, a technician uses a microscope with a numerical aperture of 1.25 and a
light source of 500 nm. What is the limit of resolution for this microscope?
A. 200 nm
B. 0.2 µm
,C. 0.5 µm
D. 250 nm
Answer: B
Conceptual Explanation: Resolution (d) = wavelength λ / (2 × NA). 500 / (2 × 1.25) = 200
nm or 0.2 µm.
3. A bacterium is isolated from a deep-sea hydrothermal vent where temperatures reach
95°C. This organism is most likely a:
A. Mesophile
B. Hyperthermophile
C. Psychrotroph
D. Thermophile
Answer: B
Conceptual Explanation: Hyperthermophiles have optimal growth temperatures
generally above 80°C, often found in volcanic or hydrothermal environments.
4. During the process of aerobic respiration, which molecule serves as the final electron
acceptor?
A. Pyruvate
B. Nitrate
C. Oxygen
, D. Sulfate
Answer: C
Conceptual Explanation: In aerobic respiration, molecular oxygen (O2) is the terminal
electron acceptor at the end of the electron transport chain.
5. A strain of E. coli has a mutation in the lacI gene, resulting in a non-functional repressor
protein. What is the expected phenotype in the absence of lactose?
A. The lac operon will be constitutively expressed.
B. The lac operon will never be expressed.
C. The lac operon will only be expressed if glucose is absent.
D. The lac operon will be expressed only when cAMP levels are low.
Answer: A
Conceptual Explanation: If the repressor is non-functional, it cannot bind to the operator
to block transcription; therefore, the operon is ‘on’ even without lactose.
6. Which of the following describes a ‘F+ to F-’ bacterial conjugation?
A. Transfer of chromosomal DNA through a pilus.
B. Uptake of naked DNA from the environment.
C. Integration of a plasmid into the host chromosome.
D. Transfer of a plasmid resulting in two F+ cells.
