WGU D311 Microbiology OA Practice Exam (2026): 80
Questions with Answers & Rationales
##、section 1 question（1–10）
**1. Which statement describes prokaryotic cells?**
A) Prokaryotic cells have a nucleus surrounded by a complex nuclear membrane
B) Prokaryotic cells have multiple rod-shaped chromosomes
C) Prokaryotic cells are found in various arrangements including coccus forms in pairs and
clusters
D) Prokaryotic cells lack a cell membrane
**Answer: C**
**Rationale:** Prokaryotic cells lack a true nucleus and membrane-bound organelles. They are
found in various arrangements including coccus (spherical) forms in pairs (diplococci) and
clusters (staphylococci).
**2. Which cellular structure is the primary site of ATP production in bacteria?**
A) Nucleus
B) Mitochondrion
C) Plasma (cytoplasmic) membrane
D) Ribosome
**Answer: C**
**Rationale:** Bacteria lack mitochondria; oxidative phosphorylation occurs across the plasma
membrane. The plasma membrane is where the electron transport chain generates ATP in
prokaryotic cells.
,**3. Which component is found exclusively in the cell wall of Gram-positive bacteria?**
A) Lipopolysaccharide
B) Outer membrane
C) Teichoic acids
D) Periplasmic space
**Answer: C**
**Rationale:** Teichoic acids are polyalcohols found in the thick peptidoglycan layer of Gram-
positive bacteria; they are absent in Gram-negative bacteria.
**4. Which structure allows bacteria to attach to surfaces and to each other?**
A) Flagella
B) Pili (fimbriae)
C) Capsule
D) Endospore
**Answer: B**
**Rationale:** Pili (fimbriae) are hair-like appendages that mediate attachment to surfaces and
host cells; flagella are for motility.
**5. The primary function of the bacterial capsule is to:**
A) Provide motility
B) Protect against phagocytosis
C) Store nutrients
D) Facilitate conjugation
**Answer: B**
,**Rationale:** Capsules are polysaccharide layers that inhibit phagocytosis and enhance
virulence. They help bacteria resist engulfment by immune cells.
**6. Which of the following is a distinguishing feature of Gram-negative bacteria?**
A) Thick peptidoglycan layer
B) Outer membrane containing lipopolysaccharide (LPS)
C) Teichoic acids
D) No cell wall
**Answer: B**
**Rationale:** Gram-negative bacteria have an outer membrane with LPS (endotoxin), which is
absent in Gram-positive bacteria. LPS Lipid A is the endotoxin component that can trigger fever
and septic shock.
**7. Endospores are produced by which genera of bacteria?**
A) Escherichia and Salmonella
B) Bacillus and Clostridium
C) Staphylococcus and Streptococcus
D) Mycobacterium and Nocardia
**Answer: B**
**Rationale:** Endospores are dormant, highly resistant structures formed by *Bacillus* and
*Clostridium* species to survive extreme heat, radiation, and dehydration.
**8. What is the primary function of peptidoglycan in bacterial cells?**
A) Promotes phagocytosis
B) Protects cells from bursting (osmotic lysis)
, C) Allows bacteria to adhere to surfaces
D) Regulates movement of substances into and out of the cell
**Answer: B**
**Rationale:** Peptidoglycan provides structural support and protection against osmotic lysis,
preventing bacterial cells from bursting in hypotonic environments.
**9. Which structure is responsible for bacterial motility?**
A) Pili
B) Capsule
C) Fimbriae
D) Flagella
**Answer: D**
**Rationale:** Flagella are long, whip-like appendages that rotate to propel bacteria through
liquid environments.
**10. Gram-positive bacteria appear purple after Gram staining because:**
A) They have an outer membrane
B) They retain the crystal violet-iodine complex due to a thick peptidoglycan layer
C) They have a thin peptidoglycan layer
D) They are counterstained with safranin
**Answer: B**
**Rationale:** The thick peptidoglycan layer in Gram-positive cells traps the crystal violet-
iodine complex, appearing purple. Gram-negative cells lose the crystal violet and appear
pink/red after safranin counterstaining.
Questions with Answers & Rationales
##、section 1 question（1–10）
**1. Which statement describes prokaryotic cells?**
A) Prokaryotic cells have a nucleus surrounded by a complex nuclear membrane
B) Prokaryotic cells have multiple rod-shaped chromosomes
C) Prokaryotic cells are found in various arrangements including coccus forms in pairs and
clusters
D) Prokaryotic cells lack a cell membrane
**Answer: C**
**Rationale:** Prokaryotic cells lack a true nucleus and membrane-bound organelles. They are
found in various arrangements including coccus (spherical) forms in pairs (diplococci) and
clusters (staphylococci).
**2. Which cellular structure is the primary site of ATP production in bacteria?**
A) Nucleus
B) Mitochondrion
C) Plasma (cytoplasmic) membrane
D) Ribosome
**Answer: C**
**Rationale:** Bacteria lack mitochondria; oxidative phosphorylation occurs across the plasma
membrane. The plasma membrane is where the electron transport chain generates ATP in
prokaryotic cells.
,**3. Which component is found exclusively in the cell wall of Gram-positive bacteria?**
A) Lipopolysaccharide
B) Outer membrane
C) Teichoic acids
D) Periplasmic space
**Answer: C**
**Rationale:** Teichoic acids are polyalcohols found in the thick peptidoglycan layer of Gram-
positive bacteria; they are absent in Gram-negative bacteria.
**4. Which structure allows bacteria to attach to surfaces and to each other?**
A) Flagella
B) Pili (fimbriae)
C) Capsule
D) Endospore
**Answer: B**
**Rationale:** Pili (fimbriae) are hair-like appendages that mediate attachment to surfaces and
host cells; flagella are for motility.
**5. The primary function of the bacterial capsule is to:**
A) Provide motility
B) Protect against phagocytosis
C) Store nutrients
D) Facilitate conjugation
**Answer: B**
,**Rationale:** Capsules are polysaccharide layers that inhibit phagocytosis and enhance
virulence. They help bacteria resist engulfment by immune cells.
**6. Which of the following is a distinguishing feature of Gram-negative bacteria?**
A) Thick peptidoglycan layer
B) Outer membrane containing lipopolysaccharide (LPS)
C) Teichoic acids
D) No cell wall
**Answer: B**
**Rationale:** Gram-negative bacteria have an outer membrane with LPS (endotoxin), which is
absent in Gram-positive bacteria. LPS Lipid A is the endotoxin component that can trigger fever
and septic shock.
**7. Endospores are produced by which genera of bacteria?**
A) Escherichia and Salmonella
B) Bacillus and Clostridium
C) Staphylococcus and Streptococcus
D) Mycobacterium and Nocardia
**Answer: B**
**Rationale:** Endospores are dormant, highly resistant structures formed by *Bacillus* and
*Clostridium* species to survive extreme heat, radiation, and dehydration.
**8. What is the primary function of peptidoglycan in bacterial cells?**
A) Promotes phagocytosis
B) Protects cells from bursting (osmotic lysis)
, C) Allows bacteria to adhere to surfaces
D) Regulates movement of substances into and out of the cell
**Answer: B**
**Rationale:** Peptidoglycan provides structural support and protection against osmotic lysis,
preventing bacterial cells from bursting in hypotonic environments.
**9. Which structure is responsible for bacterial motility?**
A) Pili
B) Capsule
C) Fimbriae
D) Flagella
**Answer: D**
**Rationale:** Flagella are long, whip-like appendages that rotate to propel bacteria through
liquid environments.
**10. Gram-positive bacteria appear purple after Gram staining because:**
A) They have an outer membrane
B) They retain the crystal violet-iodine complex due to a thick peptidoglycan layer
C) They have a thin peptidoglycan layer
D) They are counterstained with safranin
**Answer: B**
**Rationale:** The thick peptidoglycan layer in Gram-positive cells traps the crystal violet-
iodine complex, appearing purple. Gram-negative cells lose the crystal violet and appear
pink/red after safranin counterstaining.
