BIOL 271 MICROBIOLOGY WITH LAB
ADVANCED EXAMINATION
1. Which component of the Gram-negative cell wall is responsible for its endotoxic
properties?
A. Teichoic acid
B. Mycolic acid
C. Peptidoglycan
D. Lipopolysaccharide (LPS)
Answer: D
Conceptual Explanation: The Lipid A component of the Lipopolysaccharide (LPS) in the
outer membrane of Gram-negative bacteria acts as an endotoxin, triggering strong immune
responses.
2. During the Gram stain procedure, what is the specific role of Gram’s Iodine?
A. Mordant
B. Decolorizer
C. Primary stain
D. Counterstain
,Answer: A
Conceptual Explanation: Iodine acts as a mordant, forming a complex with crystal violet
that becomes trapped within the thick peptidoglycan layer of Gram-positive cells.
3. In bacterial metabolism, which pathway produces 1 ATP, 1 NADPH, and 1 NADH per
molecule of glucose, often found in Pseudomonas?
A. Glycolysis (EMP)
B. Entner-Doudoroff Pathway
C. Pentose Phosphate Pathway
D. Tricarboxylic Acid Cycle
Answer: B
Conceptual Explanation: The Entner-Doudoroff pathway is an alternative to glycolysis
used by some Gram-negative bacteria, yielding less ATP than the EMP pathway.
4. What is the primary function of dipicolinic acid in bacterial endospores?
A. Energy storage
B. Heat and desiccation resistance
C. Carbon source during germination
D. Structural support for the exosporium
Answer: B
, Conceptual Explanation: Dipicolinic acid complexes with calcium ions to dehydrate the
spore core, providing resistance to heat, chemicals, and radiation.
5. Which enzyme is responsible for relieving DNA supercoiling ahead of the replication fork?
A. DNA Polymerase III
B. DNA Ligase
C. Primase
D. DNA Gyrase (Topoisomerase II)
Answer: D
Conceptual Explanation: DNA Gyrase introduces negative supercoils or relaxes positive
supercoils to prevent DNA from overwinding during replication.
6. An Hfr (High Frequency of Recombination) bacterial strain is characterized by:
A. An F plasmid existing as a separate circular DNA
B. The integration of the F plasmid into the bacterial chromosome
C. The lack of a pilus
D. Resistance to all bacteriophages
Answer: B
Conceptual Explanation: An Hfr strain occurs when the F plasmid integrates into the host
chromosome via site-specific recombination.
ADVANCED EXAMINATION
1. Which component of the Gram-negative cell wall is responsible for its endotoxic
properties?
A. Teichoic acid
B. Mycolic acid
C. Peptidoglycan
D. Lipopolysaccharide (LPS)
Answer: D
Conceptual Explanation: The Lipid A component of the Lipopolysaccharide (LPS) in the
outer membrane of Gram-negative bacteria acts as an endotoxin, triggering strong immune
responses.
2. During the Gram stain procedure, what is the specific role of Gram’s Iodine?
A. Mordant
B. Decolorizer
C. Primary stain
D. Counterstain
,Answer: A
Conceptual Explanation: Iodine acts as a mordant, forming a complex with crystal violet
that becomes trapped within the thick peptidoglycan layer of Gram-positive cells.
3. In bacterial metabolism, which pathway produces 1 ATP, 1 NADPH, and 1 NADH per
molecule of glucose, often found in Pseudomonas?
A. Glycolysis (EMP)
B. Entner-Doudoroff Pathway
C. Pentose Phosphate Pathway
D. Tricarboxylic Acid Cycle
Answer: B
Conceptual Explanation: The Entner-Doudoroff pathway is an alternative to glycolysis
used by some Gram-negative bacteria, yielding less ATP than the EMP pathway.
4. What is the primary function of dipicolinic acid in bacterial endospores?
A. Energy storage
B. Heat and desiccation resistance
C. Carbon source during germination
D. Structural support for the exosporium
Answer: B
, Conceptual Explanation: Dipicolinic acid complexes with calcium ions to dehydrate the
spore core, providing resistance to heat, chemicals, and radiation.
5. Which enzyme is responsible for relieving DNA supercoiling ahead of the replication fork?
A. DNA Polymerase III
B. DNA Ligase
C. Primase
D. DNA Gyrase (Topoisomerase II)
Answer: D
Conceptual Explanation: DNA Gyrase introduces negative supercoils or relaxes positive
supercoils to prevent DNA from overwinding during replication.
6. An Hfr (High Frequency of Recombination) bacterial strain is characterized by:
A. An F plasmid existing as a separate circular DNA
B. The integration of the F plasmid into the bacterial chromosome
C. The lack of a pilus
D. Resistance to all bacteriophages
Answer: B
Conceptual Explanation: An Hfr strain occurs when the F plasmid integrates into the host
chromosome via site-specific recombination.
