MICROBIOLOGY MODULE 2: CELL
STRUCTURE, FUNCTION, AND
MICROSCOPY EXAM QUESTIONS AND
ANSWERS
1. Which component of the Gram-negative cell wall is primarily responsible for its toxicity and
is known as endotoxin?
A. Teichoic acid
B. Peptidoglycan
C. Lipid A of Lipopolysaccharide
D. Porin proteins
Answer: C
Conceptual Explanation: Lipid A is the toxic component of the Lipopolysaccharide (LPS)
layer found in the outer membrane of Gram-negative bacteria; it triggers a strong immune
response.
2. A microscope that uses a specialized condenser with an opaque disk to block direct light,
allowing only reflected light to enter the objective, is called a:
A. Bright-field microscope
,B. Electron microscope
C. Phase-contrast microscope
D. Dark-field microscope
Answer: D
Conceptual Explanation: Dark-field microscopy uses a dark-field condenser so that only
light reflected off the specimen enters the lens, resulting in a bright image against a dark
background.
3. What is the primary function of the bacterial glycocalyx capsule?
A. Protein synthesis
B. Protection against phagocytosis
C. Facilitating genetic exchange
D. ATP production
Answer: B
Conceptual Explanation: The capsule is an organized layer outside the cell wall that
prevents phagocytic cells (like macrophages) from engulfing the bacteria.
4. In the Gram stain procedure, what is the role of Iodine?
A. Primary stain
B. Counterstain
, C. Mordant
D. Decolorizer
Answer: C
Conceptual Explanation: Iodine acts as a mordant, forming a large Crystal Violet-Iodine
complex (CV-I) that gets trapped within the thick peptidoglycan layer of Gram-positive
cells.
5. Which of the following structures is unique to eukaryotic cells and not found in prokaryotic
cells?
A. Ribosomes
B. Mitochondria
C. Plasma membrane
D. Cytoplasm
Answer: B
Conceptual Explanation: Mitochondria are membrane-bound organelles responsible for
ATP production, which are absent in prokaryotes; prokaryotes generate ATP at the plasma
membrane.
6. Peptidoglycan is composed of alternating units of which two sugars?
A. NAG and NAM
B. Glucose and Fructose
STRUCTURE, FUNCTION, AND
MICROSCOPY EXAM QUESTIONS AND
ANSWERS
1. Which component of the Gram-negative cell wall is primarily responsible for its toxicity and
is known as endotoxin?
A. Teichoic acid
B. Peptidoglycan
C. Lipid A of Lipopolysaccharide
D. Porin proteins
Answer: C
Conceptual Explanation: Lipid A is the toxic component of the Lipopolysaccharide (LPS)
layer found in the outer membrane of Gram-negative bacteria; it triggers a strong immune
response.
2. A microscope that uses a specialized condenser with an opaque disk to block direct light,
allowing only reflected light to enter the objective, is called a:
A. Bright-field microscope
,B. Electron microscope
C. Phase-contrast microscope
D. Dark-field microscope
Answer: D
Conceptual Explanation: Dark-field microscopy uses a dark-field condenser so that only
light reflected off the specimen enters the lens, resulting in a bright image against a dark
background.
3. What is the primary function of the bacterial glycocalyx capsule?
A. Protein synthesis
B. Protection against phagocytosis
C. Facilitating genetic exchange
D. ATP production
Answer: B
Conceptual Explanation: The capsule is an organized layer outside the cell wall that
prevents phagocytic cells (like macrophages) from engulfing the bacteria.
4. In the Gram stain procedure, what is the role of Iodine?
A. Primary stain
B. Counterstain
, C. Mordant
D. Decolorizer
Answer: C
Conceptual Explanation: Iodine acts as a mordant, forming a large Crystal Violet-Iodine
complex (CV-I) that gets trapped within the thick peptidoglycan layer of Gram-positive
cells.
5. Which of the following structures is unique to eukaryotic cells and not found in prokaryotic
cells?
A. Ribosomes
B. Mitochondria
C. Plasma membrane
D. Cytoplasm
Answer: B
Conceptual Explanation: Mitochondria are membrane-bound organelles responsible for
ATP production, which are absent in prokaryotes; prokaryotes generate ATP at the plasma
membrane.
6. Peptidoglycan is composed of alternating units of which two sugars?
A. NAG and NAM
B. Glucose and Fructose
