SCI 251 Exam 4 V3 | SCI 251 Microbiology
with Intervention Skill-Based (ISB)
Experiential Learning | Q&A with
Rationale (SCI251 Exam 4) | Nightingale
College
1. Which of the following molecules is primarily responsible for presenting endogenous
antigens to Cytotoxic T cells (CD8+)?
A. MHC Class II
B. MHC Class I
C. CD4 receptors
D. B-cell receptors
Correct Answer: B
Rationale: MHC Class I molecules are found on all nucleated cells and are essential for
presenting intracellular antigens. This presentation allows the immune system to detect
and destroy host cells that are infected with viruses or have become malignant. The
interaction between MHC I and the CD8+ T cell is a fundamental component of cell-
mediated immunity.
2. Which antibody class is most associated with Type I hypersensitivity reactions and allergic
responses?
A. IgG
,B. IgM
C. IgE
D. IgA
Correct Answer: C
Rationale: IgE antibodies bind to the surface of mast cells and basophils via high-affinity Fc
receptors. When an allergen cross-links these bound IgE molecules, it triggers
degranulation and the release of histamine. This biochemical pathway leads to the clinical
symptoms observed in asthma, hay fever, and anaphylaxis.
3. The mechanism of action for penicillin involves the inhibition of which bacterial process?
A. Cell wall synthesis
B. Protein synthesis
C. DNA replication
D. Plasma membrane integrity
Correct Answer: A
Rationale: Penicillin belongs to the beta-lactam class of antibiotics which target the
transpeptidation step of peptidoglycan synthesis. By binding to penicillin-binding proteins
(PBPs), these drugs prevent the cross-linking of the bacterial cell wall. This leads to
osmotic instability and subsequent lysis of the actively dividing bacterial cell.
, 4. A patient receives an injection of pre-formed antibodies following a potential exposure to
rabies. This is an example of:
A. Naturally acquired active immunity
B. Artificially acquired active immunity
C. Artificially acquired passive immunity
D. Naturally acquired passive immunity
Correct Answer: C
Rationale: Artificially acquired passive immunity involves the transfer of antibodies from
an external source to provide immediate protection. Unlike active immunity, this process
does not stimulate the recipient’s immune system to produce its own antibodies or
memory cells. Consequently, the protection is temporary and lasts only as long as the
injected antibodies remain in circulation.
5. What is the specific role of C3b in the complement system?
A. Formation of the Membrane Attack Complex (MAC)
B. Chemotactic attraction of neutrophils
C. Opsonization of pathogens
D. Direct lysis of viral envelopes
Correct Answer: C
with Intervention Skill-Based (ISB)
Experiential Learning | Q&A with
Rationale (SCI251 Exam 4) | Nightingale
College
1. Which of the following molecules is primarily responsible for presenting endogenous
antigens to Cytotoxic T cells (CD8+)?
A. MHC Class II
B. MHC Class I
C. CD4 receptors
D. B-cell receptors
Correct Answer: B
Rationale: MHC Class I molecules are found on all nucleated cells and are essential for
presenting intracellular antigens. This presentation allows the immune system to detect
and destroy host cells that are infected with viruses or have become malignant. The
interaction between MHC I and the CD8+ T cell is a fundamental component of cell-
mediated immunity.
2. Which antibody class is most associated with Type I hypersensitivity reactions and allergic
responses?
A. IgG
,B. IgM
C. IgE
D. IgA
Correct Answer: C
Rationale: IgE antibodies bind to the surface of mast cells and basophils via high-affinity Fc
receptors. When an allergen cross-links these bound IgE molecules, it triggers
degranulation and the release of histamine. This biochemical pathway leads to the clinical
symptoms observed in asthma, hay fever, and anaphylaxis.
3. The mechanism of action for penicillin involves the inhibition of which bacterial process?
A. Cell wall synthesis
B. Protein synthesis
C. DNA replication
D. Plasma membrane integrity
Correct Answer: A
Rationale: Penicillin belongs to the beta-lactam class of antibiotics which target the
transpeptidation step of peptidoglycan synthesis. By binding to penicillin-binding proteins
(PBPs), these drugs prevent the cross-linking of the bacterial cell wall. This leads to
osmotic instability and subsequent lysis of the actively dividing bacterial cell.
, 4. A patient receives an injection of pre-formed antibodies following a potential exposure to
rabies. This is an example of:
A. Naturally acquired active immunity
B. Artificially acquired active immunity
C. Artificially acquired passive immunity
D. Naturally acquired passive immunity
Correct Answer: C
Rationale: Artificially acquired passive immunity involves the transfer of antibodies from
an external source to provide immediate protection. Unlike active immunity, this process
does not stimulate the recipient’s immune system to produce its own antibodies or
memory cells. Consequently, the protection is temporary and lasts only as long as the
injected antibodies remain in circulation.
5. What is the specific role of C3b in the complement system?
A. Formation of the Membrane Attack Complex (MAC)
B. Chemotactic attraction of neutrophils
C. Opsonization of pathogens
D. Direct lysis of viral envelopes
Correct Answer: C
