BIO 250 Exam 4 V3 | BIO 250 Microbiology
| Actual Q&A with Rationale (BIO250 Exam
4) | StraighterLine
1. Which of the following components are categorized as part of the body’s first line of
defense? (Select all that apply)
A. Intact skin
B. Mucous membranes
C. Secretion of lysozyme
D. Phagocytic white blood cells
E. Normal microbiota
F. Complement proteins
Answer: A, B, C, E
Rationale: The first line of defense includes physical, chemical, and genetic barriers that
prevent the entry of pathogens. Skin and mucous membranes provide a physical shield,
while secretions like lysozyme chemically inhibit microbial growth. Normal microbiota also
compete with potential pathogens for nutrients and space, providing microbial antagonism.
2. What is the primary function of the Major Histocompatibility Complex (MHC) Class I
molecules?
A. To present exogenous antigens to Helper T cells
,B. To initiate the classical pathway of the complement system
C. To facilitate the production of antibodies by B cells
D. To present endogenous antigens to Cytotoxic T cells
Answer: D
Rationale: MHC Class I molecules are found on all nucleated cells and are responsible for
displaying internal cellular proteins. If a cell is infected by a virus or becomes cancerous,
these molecules present abnormal peptides to CD8+ Cytotoxic T cells. This mechanism
allows the immune system to identify and destroy compromised ‘self’ cells.
3. A patient presents with a rapid, systemic allergic reaction including respiratory distress and
a drop in blood pressure after a bee sting. This is an example of which hypersensitivity type?
A. Type I Hypersensitivity
B. Type II Hypersensitivity
C. Type III Hypersensitivity
D. Type IV Hypersensitivity
Answer: A
Rationale: Type I hypersensitivity involves IgE-mediated mast cell degranulation in
response to an allergen. This specific case describes anaphylaxis, which is the most severe
systemic form of this reaction. It requires prior sensitization to the allergen and results in
the rapid release of histamine and other inflammatory mediators.
, 4. Which antimicrobial drug inhibits bacterial cell wall synthesis by blocking the cross-linking
of peptidoglycan layers?
A. Tetracycline
B. Penicillin
C. Erythromycin
D. Ciprofloxacin
Answer: B
Rationale: Penicillin belongs to the beta-lactam class of antibiotics, which target the
transpeptidase enzymes responsible for cross-linking peptidoglycan. By inhibiting these
enzymes, the bacterial cell wall becomes structurally weak, leading to osmotic lysis. This
mechanism is primarily effective against actively growing Gram-positive bacteria.
5. Which of the following are characteristics of the secondary (anamnestic) immune response
compared to the primary response? (Select all that apply)
A. Shorter lag period before antibodies appear
B. Lower overall antibody titer
C. Higher levels of IgG are produced
D. Antibodies persist for a longer duration
E. Primarily mediated by IgM antibodies
Answer: A, C, D
| Actual Q&A with Rationale (BIO250 Exam
4) | StraighterLine
1. Which of the following components are categorized as part of the body’s first line of
defense? (Select all that apply)
A. Intact skin
B. Mucous membranes
C. Secretion of lysozyme
D. Phagocytic white blood cells
E. Normal microbiota
F. Complement proteins
Answer: A, B, C, E
Rationale: The first line of defense includes physical, chemical, and genetic barriers that
prevent the entry of pathogens. Skin and mucous membranes provide a physical shield,
while secretions like lysozyme chemically inhibit microbial growth. Normal microbiota also
compete with potential pathogens for nutrients and space, providing microbial antagonism.
2. What is the primary function of the Major Histocompatibility Complex (MHC) Class I
molecules?
A. To present exogenous antigens to Helper T cells
,B. To initiate the classical pathway of the complement system
C. To facilitate the production of antibodies by B cells
D. To present endogenous antigens to Cytotoxic T cells
Answer: D
Rationale: MHC Class I molecules are found on all nucleated cells and are responsible for
displaying internal cellular proteins. If a cell is infected by a virus or becomes cancerous,
these molecules present abnormal peptides to CD8+ Cytotoxic T cells. This mechanism
allows the immune system to identify and destroy compromised ‘self’ cells.
3. A patient presents with a rapid, systemic allergic reaction including respiratory distress and
a drop in blood pressure after a bee sting. This is an example of which hypersensitivity type?
A. Type I Hypersensitivity
B. Type II Hypersensitivity
C. Type III Hypersensitivity
D. Type IV Hypersensitivity
Answer: A
Rationale: Type I hypersensitivity involves IgE-mediated mast cell degranulation in
response to an allergen. This specific case describes anaphylaxis, which is the most severe
systemic form of this reaction. It requires prior sensitization to the allergen and results in
the rapid release of histamine and other inflammatory mediators.
, 4. Which antimicrobial drug inhibits bacterial cell wall synthesis by blocking the cross-linking
of peptidoglycan layers?
A. Tetracycline
B. Penicillin
C. Erythromycin
D. Ciprofloxacin
Answer: B
Rationale: Penicillin belongs to the beta-lactam class of antibiotics, which target the
transpeptidase enzymes responsible for cross-linking peptidoglycan. By inhibiting these
enzymes, the bacterial cell wall becomes structurally weak, leading to osmotic lysis. This
mechanism is primarily effective against actively growing Gram-positive bacteria.
5. Which of the following are characteristics of the secondary (anamnestic) immune response
compared to the primary response? (Select all that apply)
A. Shorter lag period before antibodies appear
B. Lower overall antibody titer
C. Higher levels of IgG are produced
D. Antibodies persist for a longer duration
E. Primarily mediated by IgM antibodies
Answer: A, C, D
