,BIOL271/BIOL 271 Module 7 Exam | Microbiology
w/ Lab | Portage Learning | Q & A | 2026/2027
Edition (PDF)
**1. Which of the following is considered a first-line physical barrier of innate immunity?**
A) Inflammation
B) Skin
C) Complement
D) Fever
Correct Answer: Skin
Rationale: The skin is a physical barrier that prevents pathogen entry. Inflammation, complement, and
fever are part of the second line of defense, which is activated after pathogens breach the physical
barriers. The skin's outer layer, the stratum corneum, provides an impermeable physical barrier.
**2. Lysozyme, found in tears and saliva, destroys bacteria by which mechanism?**
A) Activating complement
B) Breaking down peptidoglycan in the cell wall
C) Opsonizing pathogens
D) Inducing fever
Correct Answer: Breaking down peptidoglycan in the cell wall
Rationale: Lysozyme cleaves the β-1,4 glycosidic bonds in peptidoglycan, weakening bacterial cell walls
and causing osmotic lysis. This enzyme is effective primarily against Gram-positive bacteria, which have a
thick peptidoglycan layer. It does not activate complement, opsonize pathogens, or induce fever.
**3. The mucociliary escalator in the respiratory tract functions to:**
A) Kill viruses directly
,B) Trap and move pathogens out of the airways
C) Produce antibodies
D) Activate complement
Correct Answer: Trap and move pathogens out of the airways
Rationale: The mucociliary escalator traps pathogens and particulate matter in mucus and moves them
upward toward the pharynx for expulsion or swallowing. This physical clearance mechanism is a key
component of the innate immune system's first line of defense. It does not directly kill viruses or
produce antibodies.
**4. Which of the following is a chemical barrier of the innate immune system?**
A) Mucous membranes
B) Gastric acid
C) Cilia
D) Epithelial tight junctions
Correct Answer: Gastric acid
Rationale: Gastric acid is a chemical barrier that destroys many pathogens entering the gastrointestinal
tract. Mucous membranes, cilia, and tight junctions are physical barriers. Chemical barriers include
antimicrobial peptides, lysozyme, and the acidic pH of the stomach and vagina.
**5. The complement system is a component of which line of immune defense?**
A) First line
B) Second line
C) Third line
D) Adaptive immunity only
Correct Answer: Second line
, Rationale: The complement system is part of the second line of innate immune defense, along with
inflammation, fever, and phagocytosis. It is activated when pathogens breach the physical and chemical
barriers of the first line. Complement proteins enhance opsonization, inflammation, and cytolysis.
**6. Which complement component is responsible for opsonization?**
A) C3a
B) C3b
C) C5a
D) C9
Correct Answer: C3b
Rationale: C3b coats pathogens, making them more recognizable to phagocytes with complement
receptors. This process is called opsonization. C3a and C5a are anaphylatoxins that promote
inflammation, and C9 forms the membrane attack complex (MAC) for cytolysis.
**7. The alternative complement pathway is triggered by:**
A) Antigen-antibody complexes
B) Mannose on microbial surfaces
C) Spontaneous C3 hydrolysis and stabilization on microbial surfaces
D) C1q binding to IgG
Correct Answer: Spontaneous C3 hydrolysis and stabilization on microbial surfaces
Rationale: The alternative complement pathway is antibody-independent and initiated by spontaneous
C3 hydrolysis, forming C3(H₂O) which binds factor B on pathogen surfaces. The classical pathway is
triggered by antigen-antibody complexes, and the lectin pathway is triggered by mannose-binding lectin
binding to microbial surfaces.
**8. Which of the following is NOT a function of the complement system?**
w/ Lab | Portage Learning | Q & A | 2026/2027
Edition (PDF)
**1. Which of the following is considered a first-line physical barrier of innate immunity?**
A) Inflammation
B) Skin
C) Complement
D) Fever
Correct Answer: Skin
Rationale: The skin is a physical barrier that prevents pathogen entry. Inflammation, complement, and
fever are part of the second line of defense, which is activated after pathogens breach the physical
barriers. The skin's outer layer, the stratum corneum, provides an impermeable physical barrier.
**2. Lysozyme, found in tears and saliva, destroys bacteria by which mechanism?**
A) Activating complement
B) Breaking down peptidoglycan in the cell wall
C) Opsonizing pathogens
D) Inducing fever
Correct Answer: Breaking down peptidoglycan in the cell wall
Rationale: Lysozyme cleaves the β-1,4 glycosidic bonds in peptidoglycan, weakening bacterial cell walls
and causing osmotic lysis. This enzyme is effective primarily against Gram-positive bacteria, which have a
thick peptidoglycan layer. It does not activate complement, opsonize pathogens, or induce fever.
**3. The mucociliary escalator in the respiratory tract functions to:**
A) Kill viruses directly
,B) Trap and move pathogens out of the airways
C) Produce antibodies
D) Activate complement
Correct Answer: Trap and move pathogens out of the airways
Rationale: The mucociliary escalator traps pathogens and particulate matter in mucus and moves them
upward toward the pharynx for expulsion or swallowing. This physical clearance mechanism is a key
component of the innate immune system's first line of defense. It does not directly kill viruses or
produce antibodies.
**4. Which of the following is a chemical barrier of the innate immune system?**
A) Mucous membranes
B) Gastric acid
C) Cilia
D) Epithelial tight junctions
Correct Answer: Gastric acid
Rationale: Gastric acid is a chemical barrier that destroys many pathogens entering the gastrointestinal
tract. Mucous membranes, cilia, and tight junctions are physical barriers. Chemical barriers include
antimicrobial peptides, lysozyme, and the acidic pH of the stomach and vagina.
**5. The complement system is a component of which line of immune defense?**
A) First line
B) Second line
C) Third line
D) Adaptive immunity only
Correct Answer: Second line
, Rationale: The complement system is part of the second line of innate immune defense, along with
inflammation, fever, and phagocytosis. It is activated when pathogens breach the physical and chemical
barriers of the first line. Complement proteins enhance opsonization, inflammation, and cytolysis.
**6. Which complement component is responsible for opsonization?**
A) C3a
B) C3b
C) C5a
D) C9
Correct Answer: C3b
Rationale: C3b coats pathogens, making them more recognizable to phagocytes with complement
receptors. This process is called opsonization. C3a and C5a are anaphylatoxins that promote
inflammation, and C9 forms the membrane attack complex (MAC) for cytolysis.
**7. The alternative complement pathway is triggered by:**
A) Antigen-antibody complexes
B) Mannose on microbial surfaces
C) Spontaneous C3 hydrolysis and stabilization on microbial surfaces
D) C1q binding to IgG
Correct Answer: Spontaneous C3 hydrolysis and stabilization on microbial surfaces
Rationale: The alternative complement pathway is antibody-independent and initiated by spontaneous
C3 hydrolysis, forming C3(H₂O) which binds factor B on pathogen surfaces. The classical pathway is
triggered by antigen-antibody complexes, and the lectin pathway is triggered by mannose-binding lectin
binding to microbial surfaces.
**8. Which of the following is NOT a function of the complement system?**
