D311 Microbiology with Lab - Exam 7 Practice 2026 |WGU
1. Which enzyme is responsible for synthesizing a short RNA primer to initiate
DNA replication?
A. DNA Polymerase III
B. Helicase
C. DNA Ligase
D. Primase
Answer: D
Rationale: Primase is an RNA polymerase that creates a short RNA primer, providing the
3’-OH group necessary for DNA polymerase to begin synthesis.
2. In aerobic respiration, what is the final electron acceptor?
A. Nitrate
B. Sulfate
C. Pyruvate
D. Oxygen
Answer: D
Rationale: In aerobic respiration, oxygen (O2) serves as the terminal electron acceptor at
the end of the electron transport chain.
3. Which of the following is a characteristic of Gram-positive bacteria?
A. Thin peptidoglycan layer
B. Presence of an outer membrane
C. Thick peptidoglycan layer
D. Presence of lipopolysaccharides
Answer: C
,Rationale: Gram-positive bacteria are characterized by a thick layer of peptidoglycan and
the absence of an outer membrane.
4. What is the function of the iodine in the Gram stain procedure?
A. Mordant
B. Counterstain
C. Primary stain
D. Decolorizer
Answer: A
Rationale: Iodine acts as a mordant, forming a complex with crystal violet that gets
trapped within the thick peptidoglycan of Gram-positive cells.
5. Which phase of the bacterial growth curve involves a period of little or no cell
division while the cells adjust to their new environment?
A. Log phase
B. Death phase
C. Stationary phase
D. Lag phase
Answer: D
Rationale: The lag phase is an initial period where cells are metabolically active but not yet
dividing as they prepare for growth.
6. Which type of mutation results in a premature stop codon?
A. Nonsense mutation
B. Silent mutation
C. Missense mutation
D. Frameshift mutation
Answer: A
Rationale: A nonsense mutation changes a codon for an amino acid into a stop codon,
leading to truncated protein synthesis.
, 7. What is the net gain of ATP molecules produced per molecule of glucose
during glycolysis?
A. 4 ATP
B. 2 ATP
C. 36 ATP
D. 38 ATP
Answer: B
Rationale: While 4 ATP are produced in glycolysis, 2 are consumed in the preparatory
stage, resulting in a net gain of 2 ATP.
8. Which antibody class is the first to be produced in response to a primary
infection?
A. IgG
B. IgA
C. IgM
D. IgE
Answer: C
Rationale: IgM is the first class of antibodies secreted by plasma cells during the primary
immune response.
9. Which structure allows bacteria to transfer genetic material to another cell
via conjugation?
A. Flagella
B. Pilus
C. Fimbriae
D. Capsule
Answer: B
Rationale: A sex pilus (or conjugation pilus) is used to bring two bacterial cells together to
transfer DNA.
1. Which enzyme is responsible for synthesizing a short RNA primer to initiate
DNA replication?
A. DNA Polymerase III
B. Helicase
C. DNA Ligase
D. Primase
Answer: D
Rationale: Primase is an RNA polymerase that creates a short RNA primer, providing the
3’-OH group necessary for DNA polymerase to begin synthesis.
2. In aerobic respiration, what is the final electron acceptor?
A. Nitrate
B. Sulfate
C. Pyruvate
D. Oxygen
Answer: D
Rationale: In aerobic respiration, oxygen (O2) serves as the terminal electron acceptor at
the end of the electron transport chain.
3. Which of the following is a characteristic of Gram-positive bacteria?
A. Thin peptidoglycan layer
B. Presence of an outer membrane
C. Thick peptidoglycan layer
D. Presence of lipopolysaccharides
Answer: C
,Rationale: Gram-positive bacteria are characterized by a thick layer of peptidoglycan and
the absence of an outer membrane.
4. What is the function of the iodine in the Gram stain procedure?
A. Mordant
B. Counterstain
C. Primary stain
D. Decolorizer
Answer: A
Rationale: Iodine acts as a mordant, forming a complex with crystal violet that gets
trapped within the thick peptidoglycan of Gram-positive cells.
5. Which phase of the bacterial growth curve involves a period of little or no cell
division while the cells adjust to their new environment?
A. Log phase
B. Death phase
C. Stationary phase
D. Lag phase
Answer: D
Rationale: The lag phase is an initial period where cells are metabolically active but not yet
dividing as they prepare for growth.
6. Which type of mutation results in a premature stop codon?
A. Nonsense mutation
B. Silent mutation
C. Missense mutation
D. Frameshift mutation
Answer: A
Rationale: A nonsense mutation changes a codon for an amino acid into a stop codon,
leading to truncated protein synthesis.
, 7. What is the net gain of ATP molecules produced per molecule of glucose
during glycolysis?
A. 4 ATP
B. 2 ATP
C. 36 ATP
D. 38 ATP
Answer: B
Rationale: While 4 ATP are produced in glycolysis, 2 are consumed in the preparatory
stage, resulting in a net gain of 2 ATP.
8. Which antibody class is the first to be produced in response to a primary
infection?
A. IgG
B. IgA
C. IgM
D. IgE
Answer: C
Rationale: IgM is the first class of antibodies secreted by plasma cells during the primary
immune response.
9. Which structure allows bacteria to transfer genetic material to another cell
via conjugation?
A. Flagella
B. Pilus
C. Fimbriae
D. Capsule
Answer: B
Rationale: A sex pilus (or conjugation pilus) is used to bring two bacterial cells together to
transfer DNA.
