BIOL 3200 Exam 4 Actual Exam V2 | BIOL 3200 General Microbiology
(BIOL 3200 Exam 4) | Auburn University
1. Which of the following describes the ‘parenteral route’ of microbial entry into a host?
A. Microbes deposited directly into tissues beneath the skin or mucous membranes via
punctures or bites.
B. Entry through the mucous membranes of the respiratory system.
C. Ingestion of contaminated food or water leading to entry via the GI tract.
D. Transmission from mother to fetus across the placental barrier.
Answer: A
Rationale: The parenteral route refers to entry methods that bypass typical barriers like
intact skin. This occurs when barriers are penetrated by injections, cuts, bites, or surgery.
Understanding these routes is critical for identifying how infections like Hepatitis B or HIV
are transmitted in clinical settings.
2. What is the primary difference between the ID50 and the LD50 of a pathogen?
A. ID50 measures virulence, while LD50 measures the rate of transmission.
B. There is no functional difference; they are interchangeable terms in epidemiology.
C. LD50 refers to the dose required for symptoms, whereas ID50 refers to the dose for
death.
D. ID50 is the dose required to cause infection in 50% of the test population, while LD50 is
the dose required to kill 50%.
Answer: D
Rationale: ID50 stands for the Infectious Dose for 50% of a sample population, indicating
the pathogen’s infectivity. LD50 stands for Lethal Dose for 50%, which measures the
potency or toxicity of a substance or pathogen. Comparing these values helps
microbiologists determine how dangerous a specific strain of bacteria or virus is to the
host.
3. Which bacterial enzyme is responsible for dissolving blood clots, allowing a pathogen to
spread throughout the body?
A. Kinase
B. Coagulase
C. Hyaluronidase
D. Collagenase
,Answer: A
Rationale: Kinases, such as streptokinase, break down fibrin clots that the body uses to
isolate infections. By dissolving these clots, bacteria can escape from the local site and
disseminate into other tissues. This mechanism is a key virulence factor for organisms like
Streptococcus pyogenes.
4. Exotoxins are generally produced by which type of bacteria and composed of what
macromolecule?
A. Gram-negative bacteria; Lipopolysaccharides
B. Both Gram-positive and Gram-negative; Carbohydrates
C. Gram-negative bacteria; Proteins
D. Gram-positive bacteria; Proteins
Answer: D
Rationale: Exotoxins are secreted proteins produced primarily by Gram-positive bacteria
during their growth and metabolism. They are highly specific in their effects and are among
the most lethal substances known. Because they are proteins, they can be denatured by
heat and used to form toxoids for vaccines.
5. Which component of the Gram-negative cell wall acts as an endotoxin?
A. Peptidoglycan
B. Lipid A
C. Teichoic acid
D. O-polysaccharide
Answer: B
Rationale: Endotoxins are part of the outer membrane of Gram-negative bacteria,
specifically the Lipid A portion of lipopolysaccharides (LPS). They are released when the
bacteria die and the cell wall lyses or during bacterial multiplication. Endotoxins trigger a
systemic inflammatory response, which can lead to fever, chills, and septic shock.
6. Which of the following is a classic sign of inflammation?
A. Cyanosis
B. Edema (Swelling)
C. Hypothermia
D. Bradycardia
Answer: B
, Rationale: The four classic signs of inflammation are redness (rubor), pain (dolor), heat
(calor), and swelling (edema). These signs result from increased blood flow and capillary
permeability at the site of injury or infection. Inflammation is a crucial part of the innate
immune response to contain damage and initiate repair.
7. What is the function of the membrane attack complex (MAC) in the complement system?
A. To coat the pathogen to enhance phagocytosis (opsonization).
B. To trigger the release of histamine from mast cells.
C. To create pores in the plasma membrane of the target cell, leading to cytolysis.
D. To signal T-cells to migrate to the site of infection.
Answer: C
Rationale: The complement system is a group of serum proteins that ‘complement’ the
immune response. The MAC is formed by complement proteins C5b through C9, which
insert themselves into the membrane of a pathogen. This creates holes that cause the cell to
lose its osmotic integrity and burst.
8. Which class of antibody is the most abundant in serum and can cross the placenta?
A. IgG
B. IgA
C. IgM
D. IgE
Answer: A
Rationale: IgG is the primary antibody in the blood and the only one that can cross the
placenta to provide passive immunity to the fetus. It accounts for about 80% of all
antibodies in serum. IgG is effective against bacteria, viruses, and toxins and plays a major
role in the secondary immune response.
9. A patient develops a cold after a classmate sneezes nearby. This is an example of which
type of transmission?
A. Vector transmission
B. Vehicle transmission
C. Fomite transmission
D. Droplet transmission
Answer: D
Rationale: Droplet transmission involves the discharge of microbes into the air via
sneezing, coughing, or talking over short distances (typically less than 1 meter). It is
(BIOL 3200 Exam 4) | Auburn University
1. Which of the following describes the ‘parenteral route’ of microbial entry into a host?
A. Microbes deposited directly into tissues beneath the skin or mucous membranes via
punctures or bites.
B. Entry through the mucous membranes of the respiratory system.
C. Ingestion of contaminated food or water leading to entry via the GI tract.
D. Transmission from mother to fetus across the placental barrier.
Answer: A
Rationale: The parenteral route refers to entry methods that bypass typical barriers like
intact skin. This occurs when barriers are penetrated by injections, cuts, bites, or surgery.
Understanding these routes is critical for identifying how infections like Hepatitis B or HIV
are transmitted in clinical settings.
2. What is the primary difference between the ID50 and the LD50 of a pathogen?
A. ID50 measures virulence, while LD50 measures the rate of transmission.
B. There is no functional difference; they are interchangeable terms in epidemiology.
C. LD50 refers to the dose required for symptoms, whereas ID50 refers to the dose for
death.
D. ID50 is the dose required to cause infection in 50% of the test population, while LD50 is
the dose required to kill 50%.
Answer: D
Rationale: ID50 stands for the Infectious Dose for 50% of a sample population, indicating
the pathogen’s infectivity. LD50 stands for Lethal Dose for 50%, which measures the
potency or toxicity of a substance or pathogen. Comparing these values helps
microbiologists determine how dangerous a specific strain of bacteria or virus is to the
host.
3. Which bacterial enzyme is responsible for dissolving blood clots, allowing a pathogen to
spread throughout the body?
A. Kinase
B. Coagulase
C. Hyaluronidase
D. Collagenase
,Answer: A
Rationale: Kinases, such as streptokinase, break down fibrin clots that the body uses to
isolate infections. By dissolving these clots, bacteria can escape from the local site and
disseminate into other tissues. This mechanism is a key virulence factor for organisms like
Streptococcus pyogenes.
4. Exotoxins are generally produced by which type of bacteria and composed of what
macromolecule?
A. Gram-negative bacteria; Lipopolysaccharides
B. Both Gram-positive and Gram-negative; Carbohydrates
C. Gram-negative bacteria; Proteins
D. Gram-positive bacteria; Proteins
Answer: D
Rationale: Exotoxins are secreted proteins produced primarily by Gram-positive bacteria
during their growth and metabolism. They are highly specific in their effects and are among
the most lethal substances known. Because they are proteins, they can be denatured by
heat and used to form toxoids for vaccines.
5. Which component of the Gram-negative cell wall acts as an endotoxin?
A. Peptidoglycan
B. Lipid A
C. Teichoic acid
D. O-polysaccharide
Answer: B
Rationale: Endotoxins are part of the outer membrane of Gram-negative bacteria,
specifically the Lipid A portion of lipopolysaccharides (LPS). They are released when the
bacteria die and the cell wall lyses or during bacterial multiplication. Endotoxins trigger a
systemic inflammatory response, which can lead to fever, chills, and septic shock.
6. Which of the following is a classic sign of inflammation?
A. Cyanosis
B. Edema (Swelling)
C. Hypothermia
D. Bradycardia
Answer: B
, Rationale: The four classic signs of inflammation are redness (rubor), pain (dolor), heat
(calor), and swelling (edema). These signs result from increased blood flow and capillary
permeability at the site of injury or infection. Inflammation is a crucial part of the innate
immune response to contain damage and initiate repair.
7. What is the function of the membrane attack complex (MAC) in the complement system?
A. To coat the pathogen to enhance phagocytosis (opsonization).
B. To trigger the release of histamine from mast cells.
C. To create pores in the plasma membrane of the target cell, leading to cytolysis.
D. To signal T-cells to migrate to the site of infection.
Answer: C
Rationale: The complement system is a group of serum proteins that ‘complement’ the
immune response. The MAC is formed by complement proteins C5b through C9, which
insert themselves into the membrane of a pathogen. This creates holes that cause the cell to
lose its osmotic integrity and burst.
8. Which class of antibody is the most abundant in serum and can cross the placenta?
A. IgG
B. IgA
C. IgM
D. IgE
Answer: A
Rationale: IgG is the primary antibody in the blood and the only one that can cross the
placenta to provide passive immunity to the fetus. It accounts for about 80% of all
antibodies in serum. IgG is effective against bacteria, viruses, and toxins and plays a major
role in the secondary immune response.
9. A patient develops a cold after a classmate sneezes nearby. This is an example of which
type of transmission?
A. Vector transmission
B. Vehicle transmission
C. Fomite transmission
D. Droplet transmission
Answer: D
Rationale: Droplet transmission involves the discharge of microbes into the air via
sneezing, coughing, or talking over short distances (typically less than 1 meter). It is
