D311 Microbiology with Lab Objective Assessment Practice 2026
|WGU
1. Which of the following structures is uniquely found in the cell wall of Gram-
negative bacteria?
A. Lipopolysaccharide
B. Teichoic acids
C. Peptidoglycan
D. Mycolic acid
Answer: A
Rationale: Gram-negative bacteria possess an outer membrane containing
lipopolysaccharide (LPS), whereas Gram-positive bacteria lack this and instead have a thick
layer of peptidoglycan often containing teichoic acids.
2. Which phase of the bacterial growth curve is characterized by the number of
new cells being equal to the number of dying cells?
A. Lag phase
B. Log phase
C. Death phase
D. Stationary phase
Answer: D
Rationale: In the stationary phase, growth rate slows down due to nutrient depletion and
waste accumulation, resulting in a state where the birth rate equals the death rate.
,3. What is the primary function of a bacterial endospore?
A. Reproduction
B. Motility
C. Protein synthesis
D. Survival in harsh conditions
Answer: D
Rationale: Endospores are highly resistant, dormant structures produced by some bacteria
(like Bacillus and Clostridium) to survive extreme environmental stress, not for
reproduction.
4. Which enzyme is responsible for unwinding the DNA double helix during
replication?
A. DNA Polymerase III
B. Helicase
C. Primase
D. Ligase
Answer: B
Rationale: Helicase breaks the hydrogen bonds between nitrogenous bases to unzip the
DNA double helix at the replication fork.
5. An organism that grows best at human body temperature (approximately 37
degrees Celsius) is classified as a:
A. Psychrophile
B. Mesophile
C. Thermophile
D. Hyperthermophile
Answer: B
Rationale: Mesophiles are organisms that thrive at moderate temperatures, typically
between 20 and 45 degrees Celsius, covering the human body temperature.
, 6. In the Gram stain procedure, which reagent acts as the mordant?
A. Crystal violet
B. Safranin
C. Iodine
D. 95% Ethanol
Answer: C
Rationale: Iodine acts as a mordant by forming a complex with crystal violet, which gets
trapped in the thick peptidoglycan layer of Gram-positive cells.
7. Which metabolic pathway produces the most ATP during aerobic cellular
respiration?
A. Glycolysis
B. The Krebs Cycle
C. The Electron Transport Chain
D. Fermentation
Answer: C
Rationale: The Electron Transport Chain, through oxidative phosphorylation and
chemiosmosis, generates the bulk of ATP (around 34 units) compared to the others.
8. What is the term for a virus that infects bacteria?
A. Viroid
B. Prion
C. Bacteriophage
D. Vector
Answer: C
Rationale: Bacteriophages, or phages, are viruses specifically adapted to infect and
replicate within bacterial cells.
|WGU
1. Which of the following structures is uniquely found in the cell wall of Gram-
negative bacteria?
A. Lipopolysaccharide
B. Teichoic acids
C. Peptidoglycan
D. Mycolic acid
Answer: A
Rationale: Gram-negative bacteria possess an outer membrane containing
lipopolysaccharide (LPS), whereas Gram-positive bacteria lack this and instead have a thick
layer of peptidoglycan often containing teichoic acids.
2. Which phase of the bacterial growth curve is characterized by the number of
new cells being equal to the number of dying cells?
A. Lag phase
B. Log phase
C. Death phase
D. Stationary phase
Answer: D
Rationale: In the stationary phase, growth rate slows down due to nutrient depletion and
waste accumulation, resulting in a state where the birth rate equals the death rate.
,3. What is the primary function of a bacterial endospore?
A. Reproduction
B. Motility
C. Protein synthesis
D. Survival in harsh conditions
Answer: D
Rationale: Endospores are highly resistant, dormant structures produced by some bacteria
(like Bacillus and Clostridium) to survive extreme environmental stress, not for
reproduction.
4. Which enzyme is responsible for unwinding the DNA double helix during
replication?
A. DNA Polymerase III
B. Helicase
C. Primase
D. Ligase
Answer: B
Rationale: Helicase breaks the hydrogen bonds between nitrogenous bases to unzip the
DNA double helix at the replication fork.
5. An organism that grows best at human body temperature (approximately 37
degrees Celsius) is classified as a:
A. Psychrophile
B. Mesophile
C. Thermophile
D. Hyperthermophile
Answer: B
Rationale: Mesophiles are organisms that thrive at moderate temperatures, typically
between 20 and 45 degrees Celsius, covering the human body temperature.
, 6. In the Gram stain procedure, which reagent acts as the mordant?
A. Crystal violet
B. Safranin
C. Iodine
D. 95% Ethanol
Answer: C
Rationale: Iodine acts as a mordant by forming a complex with crystal violet, which gets
trapped in the thick peptidoglycan layer of Gram-positive cells.
7. Which metabolic pathway produces the most ATP during aerobic cellular
respiration?
A. Glycolysis
B. The Krebs Cycle
C. The Electron Transport Chain
D. Fermentation
Answer: C
Rationale: The Electron Transport Chain, through oxidative phosphorylation and
chemiosmosis, generates the bulk of ATP (around 34 units) compared to the others.
8. What is the term for a virus that infects bacteria?
A. Viroid
B. Prion
C. Bacteriophage
D. Vector
Answer: C
Rationale: Bacteriophages, or phages, are viruses specifically adapted to infect and
replicate within bacterial cells.
