BIO 250 Exam 4 V1 | BIO 250 Microbiology
| Actual Q&A with Rationale (BIO250 Exam
4) | StraighterLine
1. Which of the following components are considered part of the first line of defense in the
innate immune system? Select all that apply.
A. Skin and mucous membranes
B. Chemical barriers like lysozyme and gastric juice
C. T lymphocytes
D. Ciliary escalator in the respiratory tract
E. Antibody production by plasma cells
F. Normal microbiota
Answer: A, B, D, F
Rationale: The first line of defense consists of physical and chemical barriers that prevent
pathogen entry. Skin, mucous membranes, and the ciliary escalator provide physical blocks
or removal mechanisms. Chemical factors and normal flora further inhibit colonization by
competing for resources or creating inhibitory environments.
2. Which type of hypersensitivity reaction is mediated by IgE antibodies and involves the
release of histamine from mast cells and basophils?
A. Type IV (Delayed-Type) Hypersensitivity
,B. Type II (Cytotoxic) Hypersensitivity
C. Type III (Immune Complex) Hypersensitivity
D. Type I (Anaphylactic) Hypersensitivity
Answer: D
Rationale: Type I hypersensitivity involves rapid allergic reactions triggered when
allergens bind to IgE on mast cells. This binding causes degranulation and the release of
inflammatory mediators like histamine. Examples of this reaction include asthma, hay
fever, and systemic anaphylaxis.
3. An antimicrobial drug that inhibits the synthesis of bacterial cell walls by preventing the
cross-linking of peptidoglycan is:
A. Tetracycline
B. Rifampin
C. Penicillin
D. Polymyxin B
Answer: C
Rationale: Penicillin and other beta-lactam antibiotics specifically target the
transpeptidation step in peptidoglycan synthesis. By weakening the cell wall structure, the
bacteria become susceptible to osmotic lysis. This mechanism is primarily effective against
actively growing Gram-positive bacteria.
, 4. Which of the following statements correctly describes the difference between an
endotoxin and an exotoxin?
A. Exotoxins are part of the Gram-negative cell wall, whereas endotoxins are secreted
proteins.
B. Endotoxins are lipopolysaccharides found in Gram-negative bacteria, while exotoxins
are proteins secreted by living bacteria.
C. Endotoxins are highly specific in their action, whereas exotoxins cause general systemic
effects.
D. Exotoxins are heat-stable, while endotoxins are heat-labile.
Answer: B
Rationale: Endotoxins are the lipid A component of the LPS layer in Gram-negative
bacteria and are released upon cell death. Exotoxins are potent proteins produced inside
mostly Gram-positive bacteria as part of their growth and metabolism. These two classes of
toxins differ significantly in their toxicity levels and the physiological responses they elicit.
5. Which of the following are professional antigen-presenting cells (APCs) that express MHC
class II molecules?
A. Dendritic cells
B. Macrophages
C. B cells
D. Neutrophils
| Actual Q&A with Rationale (BIO250 Exam
4) | StraighterLine
1. Which of the following components are considered part of the first line of defense in the
innate immune system? Select all that apply.
A. Skin and mucous membranes
B. Chemical barriers like lysozyme and gastric juice
C. T lymphocytes
D. Ciliary escalator in the respiratory tract
E. Antibody production by plasma cells
F. Normal microbiota
Answer: A, B, D, F
Rationale: The first line of defense consists of physical and chemical barriers that prevent
pathogen entry. Skin, mucous membranes, and the ciliary escalator provide physical blocks
or removal mechanisms. Chemical factors and normal flora further inhibit colonization by
competing for resources or creating inhibitory environments.
2. Which type of hypersensitivity reaction is mediated by IgE antibodies and involves the
release of histamine from mast cells and basophils?
A. Type IV (Delayed-Type) Hypersensitivity
,B. Type II (Cytotoxic) Hypersensitivity
C. Type III (Immune Complex) Hypersensitivity
D. Type I (Anaphylactic) Hypersensitivity
Answer: D
Rationale: Type I hypersensitivity involves rapid allergic reactions triggered when
allergens bind to IgE on mast cells. This binding causes degranulation and the release of
inflammatory mediators like histamine. Examples of this reaction include asthma, hay
fever, and systemic anaphylaxis.
3. An antimicrobial drug that inhibits the synthesis of bacterial cell walls by preventing the
cross-linking of peptidoglycan is:
A. Tetracycline
B. Rifampin
C. Penicillin
D. Polymyxin B
Answer: C
Rationale: Penicillin and other beta-lactam antibiotics specifically target the
transpeptidation step in peptidoglycan synthesis. By weakening the cell wall structure, the
bacteria become susceptible to osmotic lysis. This mechanism is primarily effective against
actively growing Gram-positive bacteria.
, 4. Which of the following statements correctly describes the difference between an
endotoxin and an exotoxin?
A. Exotoxins are part of the Gram-negative cell wall, whereas endotoxins are secreted
proteins.
B. Endotoxins are lipopolysaccharides found in Gram-negative bacteria, while exotoxins
are proteins secreted by living bacteria.
C. Endotoxins are highly specific in their action, whereas exotoxins cause general systemic
effects.
D. Exotoxins are heat-stable, while endotoxins are heat-labile.
Answer: B
Rationale: Endotoxins are the lipid A component of the LPS layer in Gram-negative
bacteria and are released upon cell death. Exotoxins are potent proteins produced inside
mostly Gram-positive bacteria as part of their growth and metabolism. These two classes of
toxins differ significantly in their toxicity levels and the physiological responses they elicit.
5. Which of the following are professional antigen-presenting cells (APCs) that express MHC
class II molecules?
A. Dendritic cells
B. Macrophages
C. B cells
D. Neutrophils
