Microbiology with Lab D311 Final Exam Version 3 2026 |WGU
1. Which of the following structures is unique to Gram-positive bacteria?
A. Lipopolysaccharide (LPS)
B. Periplasmic space
C. Peptidoglycan
D. Teichoic acids
Answer: D
Rationale: Teichoic acids are found in the thick peptidoglycan layer of Gram-positive
bacteria but are absent in Gram-negative bacteria.
2. In the Gram stain procedure, what is the role of iodine?
A. Mordant
B. Decolorizer
C. Counterstain
D. Primary stain
Answer: A
Rationale: Iodine acts as a mordant, forming a complex with crystal violet to keep the stain
inside the cell wall.
3. What is the primary function of the bacterial capsule?
A. Protection from phagocytosis
B. Energy production
C. Protein synthesis
D. Movement
Answer: A
,Rationale: The capsule is a glycocalyx layer that helps pathogens evade the host immune
system by preventing phagocytosis.
4. Which phase of the bacterial growth curve shows the fastest rate of cell
division?
A. Lag phase
B. Death phase
C. Stationary phase
D. Log phase
Answer: D
Rationale: The log (exponential) phase is characterized by constant and maximal cell
division under given conditions.
5. An organism that uses light for energy and organic compounds as a carbon
source is a:
A. Photoautotroph
B. Photoheterotroph
C. Chemoautotroph
D. Chemoheterotroph
Answer: B
Rationale: Photo- refers to light energy, and heterotroph refers to using organic carbon
sources.
6. Which enzyme is responsible for unwinding the DNA double helix during
replication?
A. DNA Polymerase
B. Primase
C. Helicase
D. Ligase
Answer: C
, Rationale: Helicase breaks the hydrogen bonds between bases to unzip the DNA strands.
7. Which of the following is a byproduct of fermentation?
A. Pyruvate
B. Glucose
C. Lactic acid
D. Oxygen
Answer: C
Rationale: Fermentation reduces pyruvate into end products like lactic acid or ethanol to
recycle NAD+.
8. The transfer of DNA from one bacterium to another via a bacteriophage is
called:
A. Conjugation
B. Transduction
C. Transformation
D. Translation
Answer: B
Rationale: Transduction involves a viral vector (phage) carrying bacterial DNA between
cells.
9. Which antibody class is the first to be produced during a primary immune
response?
A. IgG
B. IgA
C. IgM
D. IgE
Answer: C
1. Which of the following structures is unique to Gram-positive bacteria?
A. Lipopolysaccharide (LPS)
B. Periplasmic space
C. Peptidoglycan
D. Teichoic acids
Answer: D
Rationale: Teichoic acids are found in the thick peptidoglycan layer of Gram-positive
bacteria but are absent in Gram-negative bacteria.
2. In the Gram stain procedure, what is the role of iodine?
A. Mordant
B. Decolorizer
C. Counterstain
D. Primary stain
Answer: A
Rationale: Iodine acts as a mordant, forming a complex with crystal violet to keep the stain
inside the cell wall.
3. What is the primary function of the bacterial capsule?
A. Protection from phagocytosis
B. Energy production
C. Protein synthesis
D. Movement
Answer: A
,Rationale: The capsule is a glycocalyx layer that helps pathogens evade the host immune
system by preventing phagocytosis.
4. Which phase of the bacterial growth curve shows the fastest rate of cell
division?
A. Lag phase
B. Death phase
C. Stationary phase
D. Log phase
Answer: D
Rationale: The log (exponential) phase is characterized by constant and maximal cell
division under given conditions.
5. An organism that uses light for energy and organic compounds as a carbon
source is a:
A. Photoautotroph
B. Photoheterotroph
C. Chemoautotroph
D. Chemoheterotroph
Answer: B
Rationale: Photo- refers to light energy, and heterotroph refers to using organic carbon
sources.
6. Which enzyme is responsible for unwinding the DNA double helix during
replication?
A. DNA Polymerase
B. Primase
C. Helicase
D. Ligase
Answer: C
, Rationale: Helicase breaks the hydrogen bonds between bases to unzip the DNA strands.
7. Which of the following is a byproduct of fermentation?
A. Pyruvate
B. Glucose
C. Lactic acid
D. Oxygen
Answer: C
Rationale: Fermentation reduces pyruvate into end products like lactic acid or ethanol to
recycle NAD+.
8. The transfer of DNA from one bacterium to another via a bacteriophage is
called:
A. Conjugation
B. Transduction
C. Transformation
D. Translation
Answer: B
Rationale: Transduction involves a viral vector (phage) carrying bacterial DNA between
cells.
9. Which antibody class is the first to be produced during a primary immune
response?
A. IgG
B. IgA
C. IgM
D. IgE
Answer: C
