MCB 3020C Exam 4 V2 | MCB 3020C General Microbiology | Actual
Q&A with Rationale (MCB3020C Exam 4) | University of Central
Florida
1. Which immunoglobulin class is the most abundant in serum and is capable of crossing the
placenta to provide passive immunity to the fetus?
A. IgM
B. IgG
C. IgA
D. IgE
Answer: B
Explanation: IgG is the primary antibody of the secondary immune response and makes
up approximately 80% of serum antibodies. Its unique structure allows it to cross the
placental barrier, providing essential protection to the developing fetus. This molecule is
also highly effective at opsonization and neutralizing toxins.
2. Which of the following describes the function of MHC Class I molecules?
A. Presenting endogenous antigens to CD8+ T cells
B. Presenting exogenous antigens to CD4+ T cells
C. Directly lysing bacterial cell walls
D. Acting as a receptor for the Fc region of antibodies
Answer: A
Explanation: MHC Class I molecules are found on all nucleated cells in the human body.
They present fragments of proteins synthesized within the cell, such as viral or tumor
proteins, to Cytotoxic T lymphocytes. This mechanism allows the immune system to
identify and destroy infected or abnormal host cells.
3. A patient presents with a systemic inflammatory response triggered by the release of Lipid
A from Gram-negative bacteria. This substance is known as:
A. Exotoxin
B. Enterotoxin
C. Neurotoxin
D. Endotoxin
Answer: D
,Explanation: Endotoxins are integral components of the outer membrane of Gram-
negative bacteria, specifically the Lipid A portion of lipopolysaccharide (LPS). They are
released primarily when the bacteria die and the cell wall breaks apart. The release of large
amounts can lead to septic shock, characterized by a dangerous drop in blood pressure.
4. Which type of hypersensitivity reaction is mediated by IgE antibodies and involves the
degranulation of mast cells and basophils?
A. Type II (Cytotoxic)
B. Type IV (Delayed-type)
C. Type III (Immune Complex)
D. Type I (Immediate)
Answer: D
Explanation: Type I hypersensitivity occurs within minutes of exposure to an allergen in a
previously sensitized individual. IgE antibodies bind to mast cells, and subsequent allergen
cross-linking triggers the release of histamine and other inflammatory mediators. Common
examples include hay fever, asthma, and systemic anaphylaxis.
5. The process by which antibodies coat a pathogen to enhance its ingestion by phagocytes is
called:
A. Complement fixation
B. Agglutination
C. Neutralization
D. Opsonization
Answer: D
Explanation: Opsonization involves the binding of opsonins, such as IgG or C3b, to the
surface of a microbe. This process effectively ‘flags’ the pathogen for recognition by
phagocytic cells like macrophages and neutrophils. Phagocytes possess receptors for these
opsonins, which significantly increases the efficiency of phagocytosis.
6. Which complement component is responsible for the formation of the Membrane Attack
Complex (MAC)?
A. C5b through C9
B. C3a
C. C1
D. C4
Answer: A
, Explanation: The Membrane Attack Complex is the end product of the complement
cascade. It begins with the cleavage of C5 into C5a and C5b, where C5b recruits C6, C7, C8,
and multiple C9 molecules. These proteins insert into the target cell membrane, creating
pores that lead to osmotic lysis.
7. What is the primary role of Helper T cells (CD4+) in the immune response?
A. Directly killing virally infected cells
B. Secreting cytokines to coordinate the immune response
C. Producing large quantities of soluble antibodies
D. Phagocytizing extracellular bacteria
Answer: B
Explanation: Helper T cells are the central coordinators of the adaptive immune system.
Upon recognizing antigens presented on MHC II, they release various cytokines that
activate B cells and Cytotoxic T cells. Without Helper T cells, the immune system cannot
mount an effective response to most pathogens.
8. Which of the following is an example of naturally acquired passive immunity?
A. Vaccination against Hepatitis B
B. Transfer of antibodies through breast milk
C. Recovery from a bout of measles
D. Injection of antitoxin for snake venom
Answer: B
Explanation: Passive immunity involves the transfer of pre-formed antibodies from one
individual to another. Natural passive immunity occurs when a mother passes IgA to her
infant via colostrum and breast milk. This provides immediate but temporary protection
until the infant’s own immune system matures.
9. Which enzyme produced by some bacteria breaks down the ‘glue’ that holds connective
tissue cells together, allowing the pathogen to spread?
A. Coagulase
B. Kinase
C. Collagenase
D. Hyaluronidase
Answer: D
Explanation: Hyaluronidase is a virulence factor that degrades hyaluronic acid, a major
component of the extracellular matrix in connective tissues. By breaking down this
Q&A with Rationale (MCB3020C Exam 4) | University of Central
Florida
1. Which immunoglobulin class is the most abundant in serum and is capable of crossing the
placenta to provide passive immunity to the fetus?
A. IgM
B. IgG
C. IgA
D. IgE
Answer: B
Explanation: IgG is the primary antibody of the secondary immune response and makes
up approximately 80% of serum antibodies. Its unique structure allows it to cross the
placental barrier, providing essential protection to the developing fetus. This molecule is
also highly effective at opsonization and neutralizing toxins.
2. Which of the following describes the function of MHC Class I molecules?
A. Presenting endogenous antigens to CD8+ T cells
B. Presenting exogenous antigens to CD4+ T cells
C. Directly lysing bacterial cell walls
D. Acting as a receptor for the Fc region of antibodies
Answer: A
Explanation: MHC Class I molecules are found on all nucleated cells in the human body.
They present fragments of proteins synthesized within the cell, such as viral or tumor
proteins, to Cytotoxic T lymphocytes. This mechanism allows the immune system to
identify and destroy infected or abnormal host cells.
3. A patient presents with a systemic inflammatory response triggered by the release of Lipid
A from Gram-negative bacteria. This substance is known as:
A. Exotoxin
B. Enterotoxin
C. Neurotoxin
D. Endotoxin
Answer: D
,Explanation: Endotoxins are integral components of the outer membrane of Gram-
negative bacteria, specifically the Lipid A portion of lipopolysaccharide (LPS). They are
released primarily when the bacteria die and the cell wall breaks apart. The release of large
amounts can lead to septic shock, characterized by a dangerous drop in blood pressure.
4. Which type of hypersensitivity reaction is mediated by IgE antibodies and involves the
degranulation of mast cells and basophils?
A. Type II (Cytotoxic)
B. Type IV (Delayed-type)
C. Type III (Immune Complex)
D. Type I (Immediate)
Answer: D
Explanation: Type I hypersensitivity occurs within minutes of exposure to an allergen in a
previously sensitized individual. IgE antibodies bind to mast cells, and subsequent allergen
cross-linking triggers the release of histamine and other inflammatory mediators. Common
examples include hay fever, asthma, and systemic anaphylaxis.
5. The process by which antibodies coat a pathogen to enhance its ingestion by phagocytes is
called:
A. Complement fixation
B. Agglutination
C. Neutralization
D. Opsonization
Answer: D
Explanation: Opsonization involves the binding of opsonins, such as IgG or C3b, to the
surface of a microbe. This process effectively ‘flags’ the pathogen for recognition by
phagocytic cells like macrophages and neutrophils. Phagocytes possess receptors for these
opsonins, which significantly increases the efficiency of phagocytosis.
6. Which complement component is responsible for the formation of the Membrane Attack
Complex (MAC)?
A. C5b through C9
B. C3a
C. C1
D. C4
Answer: A
, Explanation: The Membrane Attack Complex is the end product of the complement
cascade. It begins with the cleavage of C5 into C5a and C5b, where C5b recruits C6, C7, C8,
and multiple C9 molecules. These proteins insert into the target cell membrane, creating
pores that lead to osmotic lysis.
7. What is the primary role of Helper T cells (CD4+) in the immune response?
A. Directly killing virally infected cells
B. Secreting cytokines to coordinate the immune response
C. Producing large quantities of soluble antibodies
D. Phagocytizing extracellular bacteria
Answer: B
Explanation: Helper T cells are the central coordinators of the adaptive immune system.
Upon recognizing antigens presented on MHC II, they release various cytokines that
activate B cells and Cytotoxic T cells. Without Helper T cells, the immune system cannot
mount an effective response to most pathogens.
8. Which of the following is an example of naturally acquired passive immunity?
A. Vaccination against Hepatitis B
B. Transfer of antibodies through breast milk
C. Recovery from a bout of measles
D. Injection of antitoxin for snake venom
Answer: B
Explanation: Passive immunity involves the transfer of pre-formed antibodies from one
individual to another. Natural passive immunity occurs when a mother passes IgA to her
infant via colostrum and breast milk. This provides immediate but temporary protection
until the infant’s own immune system matures.
9. Which enzyme produced by some bacteria breaks down the ‘glue’ that holds connective
tissue cells together, allowing the pathogen to spread?
A. Coagulase
B. Kinase
C. Collagenase
D. Hyaluronidase
Answer: D
Explanation: Hyaluronidase is a virulence factor that degrades hyaluronic acid, a major
component of the extracellular matrix in connective tissues. By breaking down this
