BIOS 242 MICROBIOLOGY
COMPREHENSIVE PRACTICE EXAM
QUESTIONS AND ANSWERS
1. Which of the following components is uniquely found in the cell wall of Acid-fast bacteria
such as Mycobacterium tuberculosis?
A. Teichoic acids
B. Lipopolysaccharide (LPS)
C. Mycolic acids
D. Pseudomurein
Answer: C
Conceptual Explanation: Acid-fast bacteria possess a waxy cell wall containing high
concentrations of mycolic acids, which resist traditional Gram staining.
2. During the process of Glycolysis, what is the net gain of ATP molecules per molecule of
glucose oxidized?
A. 2 ATP
B. 38 ATP
,C. 4 ATP
D. 36 ATP
Answer: A
Conceptual Explanation: While 4 ATP are produced, 2 are consumed in the preparatory
stage, resulting in a net gain of 2 ATP.
3. Which enzyme is responsible for relieving the supercoiling of DNA ahead of the replication
fork during bacterial DNA replication?
A. DNA Helicase
B. DNA Gyrase (Topoisomerase II)
C. DNA Ligase
D. DNA Polymerase III
Answer: B
Conceptual Explanation: DNA Gyrase introduces negative supercoils to counteract the
positive supercoiling caused by the unwinding of the double helix.
4. In the Lac operon model, what occurs when lactose is present but glucose is absent?
A. cAMP levels are high and CAP binds to the promoter, facilitating high transcription
B. Transcription is inhibited by the repressor
C. The repressor binds to the operator preventing RNA polymerase from moving
, D. Transcription occurs at a very low, basal level
Answer: A
Conceptual Explanation: When glucose is absent, cAMP levels rise, activating CAP. When
lactose is present, the repressor is inactivated, allowing high levels of transcription.
5. Which type of horizontal gene transfer requires direct cell-to-cell contact through a pilus?
A. Conjugation
B. Transduction
C. Transformation
D. Transposition
Answer: A
Conceptual Explanation: Conjugation involves the transfer of genetic material (usually
plasmids) from a donor cell to a recipient cell via a sex pilus.
6. Which of the following is a characteristic of a facultative anaerobe?
A. It cannot grow in the presence of oxygen
B. It is killed by superoxide dismutase
C. It requires a small amount of oxygen (2-10%) for growth
D. It grows better in the presence of oxygen but can grow without it
Answer: D
COMPREHENSIVE PRACTICE EXAM
QUESTIONS AND ANSWERS
1. Which of the following components is uniquely found in the cell wall of Acid-fast bacteria
such as Mycobacterium tuberculosis?
A. Teichoic acids
B. Lipopolysaccharide (LPS)
C. Mycolic acids
D. Pseudomurein
Answer: C
Conceptual Explanation: Acid-fast bacteria possess a waxy cell wall containing high
concentrations of mycolic acids, which resist traditional Gram staining.
2. During the process of Glycolysis, what is the net gain of ATP molecules per molecule of
glucose oxidized?
A. 2 ATP
B. 38 ATP
,C. 4 ATP
D. 36 ATP
Answer: A
Conceptual Explanation: While 4 ATP are produced, 2 are consumed in the preparatory
stage, resulting in a net gain of 2 ATP.
3. Which enzyme is responsible for relieving the supercoiling of DNA ahead of the replication
fork during bacterial DNA replication?
A. DNA Helicase
B. DNA Gyrase (Topoisomerase II)
C. DNA Ligase
D. DNA Polymerase III
Answer: B
Conceptual Explanation: DNA Gyrase introduces negative supercoils to counteract the
positive supercoiling caused by the unwinding of the double helix.
4. In the Lac operon model, what occurs when lactose is present but glucose is absent?
A. cAMP levels are high and CAP binds to the promoter, facilitating high transcription
B. Transcription is inhibited by the repressor
C. The repressor binds to the operator preventing RNA polymerase from moving
, D. Transcription occurs at a very low, basal level
Answer: A
Conceptual Explanation: When glucose is absent, cAMP levels rise, activating CAP. When
lactose is present, the repressor is inactivated, allowing high levels of transcription.
5. Which type of horizontal gene transfer requires direct cell-to-cell contact through a pilus?
A. Conjugation
B. Transduction
C. Transformation
D. Transposition
Answer: A
Conceptual Explanation: Conjugation involves the transfer of genetic material (usually
plasmids) from a donor cell to a recipient cell via a sex pilus.
6. Which of the following is a characteristic of a facultative anaerobe?
A. It cannot grow in the presence of oxygen
B. It is killed by superoxide dismutase
C. It requires a small amount of oxygen (2-10%) for growth
D. It grows better in the presence of oxygen but can grow without it
Answer: D
