ESTUDYR
NATS 1670 QUIZ 3 UPDATED EXAM WITH MOST TESTED
QUESTIONS AND ANSWERS | GRADED A+ | ASSURED
SUCCESS WITH DETAILED RATIONALES
Immunology & Host Defense — Intensive MCQs
1. What is Clostridium difficile?
A. A virus that causes respiratory infections
B. A protozoan that causes malaria
C. An anaerobic fungus that infects skin
D. A bacterium that causes infectious diarrhea/colitis, often after antibiotics (nosocomial)
Rationale: C. difficile is a Gram-positive, spore-forming bacterium associated with antibiotic-
associated colitis and is commonly acquired in healthcare settings.
2. Which of the following can occur when immunity is excessive or misdirected?
A. Allergy
B. Autoimmune disease
C. Cytokine storm / acute overwhelming inflammation (sepsis)
D. All of the above
Rationale: Too much or dysregulated immune activity can cause hypersensitivity (allergy),
autoimmunity, or systemic hyperinflammation (cytokine storm/septic shock).
3. Which three “stages” or levels of host defense are commonly described?
A. Mechanical, Chemical, Thermal
B. Primary, Secondary, Tertiary
C. Intrinsic (barriers), Innate immunity, Acquired (adaptive) immunity
D. Cellular, Humoral, Neural
Rationale: Host defense is often grouped as barrier/intrinsic defenses (skin, mucosa), fast innate
responses, and slower adaptive (acquired) immunity.
4. Which of the following are defenses at the skin level?
A. Outer epidermal layer only
B. Normal flora only
,ESTUDYR
C. Sweat/flushing and phospholipid barrier only
D. All of the above: outer skin layer, resident normal flora, flushing (sweat), lipid barriers
Rationale: Skin provides a physical barrier, hosts protective microbiota, and secretes substances
(sweat, lipids) that deter pathogens.
5. Which mechanisms help prevent infection in the gastrointestinal (GI) tract?
A. Peristalsis, low gastric pH, bile salts
B. Only digestive enzymes
C. Only chewing and saliva
D. A — peristalsis, acidic stomach pH, and bile salts
Rationale: Mechanical movement, acidic environment, and bile/surfactants limit colonization by
many microbes.
6. What protects the nasopharynx and eye from microbes?
A. Saliva, mucus, tears, lysozyme and flushing actions
B. Hair only
C. Skin thickness only
D. A — mucus, saliva, tears, flushing and lysozyme
Rationale: Mucosal secretions, tears and antimicrobial enzymes (e.g., lysozyme) trap and
destroy microbes.
7. Which is an advantage of innate immunity?
A. Requires days to respond
B. Highly specific memory formation
C. Immediate response; one cell can recognize many pathogen types
D. Only acts after adaptive immunity
Rationale: Innate defenses act rapidly and recognize broad molecular patterns on pathogens.
8. Which are characteristics of adaptive (acquired) immunity?
A. Immediate action, non-specific
B. No memory, broad recognition
C. Slow onset (days), high specificity, and produces immunological memory
D. Only present in invertebrates
Rationale: Adaptive responses are slower to start but generate specific memory cells (B and T
cell responses).
, ESTUDYR
9. One possible reason dogs eat feces (coprophagy) is:
A. Because it tastes sweet only
B. Because they are dehydrated
C. To repopulate gut flora (in some contexts)
D. Because they cannot digest anything else
Rationale: Coprophagy can reintroduce beneficial microbes/enzymes or be behavioral; it’s one
of several reasons, including nutritional or behavioral causes.
10. What is the approximate pH of the human stomach (fasting)?
A. 5-6
B. 3-4
C. ~1–2
D. 7 (neutral)
Rationale: Gastric acid is very strong (pH ≈1–2), which helps kill ingested microbes.
11. Why do many bacteria possess cell walls?
A. To perform photosynthesis
B. To move faster
C. To help maintain osmotic pressure and structural integrity
D. To secrete antibodies
Rationale: Cell walls (peptidoglycan in bacteria) protect against osmotic lysis and give shape and
rigidity.
12. Which disease frequently requires an updated vaccine each year due to antigenic change?
A. Measles
B. Polio
C. Influenza
D. Tetanus
Rationale: Influenza viruses undergo antigenic drift and shift, necessitating annual vaccine
updates.
13. Which of the following lists primary and secondary lymphoid organs correctly?
A. Primary: spleen; Secondary: bone marrow, thymus
B. Primary: bone marrow, thymus — Secondary: adenoids, tonsils, lymph nodes, spleen,
Peyer’s patches, appendix
C. Primary: appendix only; Secondary: liver only
NATS 1670 QUIZ 3 UPDATED EXAM WITH MOST TESTED
QUESTIONS AND ANSWERS | GRADED A+ | ASSURED
SUCCESS WITH DETAILED RATIONALES
Immunology & Host Defense — Intensive MCQs
1. What is Clostridium difficile?
A. A virus that causes respiratory infections
B. A protozoan that causes malaria
C. An anaerobic fungus that infects skin
D. A bacterium that causes infectious diarrhea/colitis, often after antibiotics (nosocomial)
Rationale: C. difficile is a Gram-positive, spore-forming bacterium associated with antibiotic-
associated colitis and is commonly acquired in healthcare settings.
2. Which of the following can occur when immunity is excessive or misdirected?
A. Allergy
B. Autoimmune disease
C. Cytokine storm / acute overwhelming inflammation (sepsis)
D. All of the above
Rationale: Too much or dysregulated immune activity can cause hypersensitivity (allergy),
autoimmunity, or systemic hyperinflammation (cytokine storm/septic shock).
3. Which three “stages” or levels of host defense are commonly described?
A. Mechanical, Chemical, Thermal
B. Primary, Secondary, Tertiary
C. Intrinsic (barriers), Innate immunity, Acquired (adaptive) immunity
D. Cellular, Humoral, Neural
Rationale: Host defense is often grouped as barrier/intrinsic defenses (skin, mucosa), fast innate
responses, and slower adaptive (acquired) immunity.
4. Which of the following are defenses at the skin level?
A. Outer epidermal layer only
B. Normal flora only
,ESTUDYR
C. Sweat/flushing and phospholipid barrier only
D. All of the above: outer skin layer, resident normal flora, flushing (sweat), lipid barriers
Rationale: Skin provides a physical barrier, hosts protective microbiota, and secretes substances
(sweat, lipids) that deter pathogens.
5. Which mechanisms help prevent infection in the gastrointestinal (GI) tract?
A. Peristalsis, low gastric pH, bile salts
B. Only digestive enzymes
C. Only chewing and saliva
D. A — peristalsis, acidic stomach pH, and bile salts
Rationale: Mechanical movement, acidic environment, and bile/surfactants limit colonization by
many microbes.
6. What protects the nasopharynx and eye from microbes?
A. Saliva, mucus, tears, lysozyme and flushing actions
B. Hair only
C. Skin thickness only
D. A — mucus, saliva, tears, flushing and lysozyme
Rationale: Mucosal secretions, tears and antimicrobial enzymes (e.g., lysozyme) trap and
destroy microbes.
7. Which is an advantage of innate immunity?
A. Requires days to respond
B. Highly specific memory formation
C. Immediate response; one cell can recognize many pathogen types
D. Only acts after adaptive immunity
Rationale: Innate defenses act rapidly and recognize broad molecular patterns on pathogens.
8. Which are characteristics of adaptive (acquired) immunity?
A. Immediate action, non-specific
B. No memory, broad recognition
C. Slow onset (days), high specificity, and produces immunological memory
D. Only present in invertebrates
Rationale: Adaptive responses are slower to start but generate specific memory cells (B and T
cell responses).
, ESTUDYR
9. One possible reason dogs eat feces (coprophagy) is:
A. Because it tastes sweet only
B. Because they are dehydrated
C. To repopulate gut flora (in some contexts)
D. Because they cannot digest anything else
Rationale: Coprophagy can reintroduce beneficial microbes/enzymes or be behavioral; it’s one
of several reasons, including nutritional or behavioral causes.
10. What is the approximate pH of the human stomach (fasting)?
A. 5-6
B. 3-4
C. ~1–2
D. 7 (neutral)
Rationale: Gastric acid is very strong (pH ≈1–2), which helps kill ingested microbes.
11. Why do many bacteria possess cell walls?
A. To perform photosynthesis
B. To move faster
C. To help maintain osmotic pressure and structural integrity
D. To secrete antibodies
Rationale: Cell walls (peptidoglycan in bacteria) protect against osmotic lysis and give shape and
rigidity.
12. Which disease frequently requires an updated vaccine each year due to antigenic change?
A. Measles
B. Polio
C. Influenza
D. Tetanus
Rationale: Influenza viruses undergo antigenic drift and shift, necessitating annual vaccine
updates.
13. Which of the following lists primary and secondary lymphoid organs correctly?
A. Primary: spleen; Secondary: bone marrow, thymus
B. Primary: bone marrow, thymus — Secondary: adenoids, tonsils, lymph nodes, spleen,
Peyer’s patches, appendix
C. Primary: appendix only; Secondary: liver only
