BIO 250 Exam 4 V2 | BIO 250 Microbiology | Actual Q&A with
Rationale (BIO250 Exam 4) | StraighterLine
1. Which of the following are characteristics of the innate immune system? Select all that
apply.
A. Highly specific recognition of molecular patterns.
B. Immediate response to infection.
C. Presence of immunological memory.
D. Includes physical and chemical barriers.
E. Options B, D, and E are correct.
F. Involves cells such as neutrophils and natural killer cells.
Correct Answer: E
Explanation: The innate immune system is the first line of defense and acts non-
specifically and immediately upon exposure to pathogens. It includes physical barriers like
skin and chemical barriers like stomach acid, alongside cellular components such as
phagocytes and NK cells. Unlike the adaptive system, it does not possess immunological
memory or the fine-tuned specificity of antibodies.
2. A patient presents with a high fever, stiff neck, and a petechial rash. A lumbar puncture
reveals Gram-negative diplococci in the cerebrospinal fluid. Which organism is the most likely
causative agent?
A. Neisseria meningitidis
B. Streptococcus pneumoniae
C. Haemophilus influenzae
D. Listeria monocytogenes
Correct Answer: A
Explanation: Neisseria meningitidis is a Gram-negative diplococcus that is a leading cause
of bacterial meningitis. The presence of a petechial rash is a characteristic clinical sign of
meningococcal septicemia. Prompt diagnosis and treatment are critical due to the rapid
progression of this life-threatening infection.
3. What is the primary mechanism of action of penicillin and other beta-lactam antibiotics?
A. Inhibition of protein synthesis by binding to the 50S ribosomal subunit.
B. Disruption of the bacterial cytoplasmic membrane.
,C. Interference with DNA replication by inhibiting DNA gyrase.
D. Inhibition of peptidoglycan synthesis by binding to transpeptidase enzymes.
Correct Answer: D
Explanation: Beta-lactam antibiotics work by interfering with the synthesis of the
bacterial cell wall, specifically the cross-linking of peptidoglycan chains. They bind to
penicillin-binding proteins (PBPs), such as transpeptidase, which prevents the cell from
maintaining structural integrity. This leads to osmotic lysis and death of the bacterial cell.
4. Which of the following clinical signs are considered the cardinal signs of inflammation?
Select all that apply.
A. Redness (Rubor)
B. Heat (Calor)
C. Swelling (Tumor)
D. All of the above are cardinal signs.
E. Loss of function (Functio laesa)
F. Pain (Dolor)
Correct Answer: D
Explanation: The inflammatory response is characterized by five classic signs: redness,
heat, swelling, and pain, which were identified in ancient times. Loss of function was added
later as a fifth sign to reflect the impact on the affected tissue. These signs result from
increased blood flow, increased capillary permeability, and the recruitment of immune
cells to the site of injury.
5. A 5-year-old child presents with a ‘barking’ cough and inspiratory stridor. Which virus is the
most common cause of this condition, known as croup?
A. Parainfluenza virus
B. Respiratory Syncytial Virus (RSV)
C. Influenza A virus
D. Adenovirus
Correct Answer: A
Explanation: Croup, or laryngotracheobronchitis, is most frequently caused by
Parainfluenza viruses, particularly type 1. It is characterized by inflammation of the upper
airway, leading to the distinctive ‘seal-like’ barking cough. While RSV and Adenovirus can
cause respiratory symptoms, Parainfluenza is the classic etiologic agent for croup in
pediatric populations.
, 6. Which of the following describes the function of the enzyme reverse transcriptase in the
life cycle of HIV?
A. Cleaving large viral polyproteins into functional units.
B. Converting the viral RNA genome into a double-stranded DNA copy.
C. Integrating the viral genome into the host cell’s DNA.
D. Assisting in the attachment of the virus to the CD4 receptor.
Correct Answer: B
Explanation: Reverse transcriptase is an essential enzyme for retroviruses like HIV, as it
allows the conversion of single-stranded RNA into double-stranded DNA. This newly
synthesized DNA can then be transported into the nucleus and integrated into the host
genome. This step is a primary target for many antiretroviral therapies used to manage
HIV/AIDS.
7. Which organism is commonly associated with gastrointestinal infections following the
consumption of undercooked poultry or contaminated eggs?
A. Salmonella enterica
B. Shigella sonnei
C. Vibrio cholerae
D. Clostridium difficile
Correct Answer: A
Explanation: Salmonella enterica is a major cause of bacterial gastroenteritis worldwide,
often linked to poultry, eggs, and dairy products. The bacteria colonize the intestinal
epithelium, causing symptoms such as diarrhea, abdominal cramps, and fever. Proper food
handling and cooking are the most effective ways to prevent salmonellosis.
8. The Mantoux skin test is used to screen for exposure to which pathogen?
A. Staphylococcus aureus
B. Corynebacterium diphtheriae
C. Mycobacterium tuberculosis
D. Bordetella pertussis
Correct Answer: C
Explanation: The Mantoux test, also known as the PPD (Purified Protein Derivative) test,
screens for Mycobacterium tuberculosis infection. It relies on a Type IV delayed-type
hypersensitivity reaction, where an induration at the injection site indicates prior exposure
Rationale (BIO250 Exam 4) | StraighterLine
1. Which of the following are characteristics of the innate immune system? Select all that
apply.
A. Highly specific recognition of molecular patterns.
B. Immediate response to infection.
C. Presence of immunological memory.
D. Includes physical and chemical barriers.
E. Options B, D, and E are correct.
F. Involves cells such as neutrophils and natural killer cells.
Correct Answer: E
Explanation: The innate immune system is the first line of defense and acts non-
specifically and immediately upon exposure to pathogens. It includes physical barriers like
skin and chemical barriers like stomach acid, alongside cellular components such as
phagocytes and NK cells. Unlike the adaptive system, it does not possess immunological
memory or the fine-tuned specificity of antibodies.
2. A patient presents with a high fever, stiff neck, and a petechial rash. A lumbar puncture
reveals Gram-negative diplococci in the cerebrospinal fluid. Which organism is the most likely
causative agent?
A. Neisseria meningitidis
B. Streptococcus pneumoniae
C. Haemophilus influenzae
D. Listeria monocytogenes
Correct Answer: A
Explanation: Neisseria meningitidis is a Gram-negative diplococcus that is a leading cause
of bacterial meningitis. The presence of a petechial rash is a characteristic clinical sign of
meningococcal septicemia. Prompt diagnosis and treatment are critical due to the rapid
progression of this life-threatening infection.
3. What is the primary mechanism of action of penicillin and other beta-lactam antibiotics?
A. Inhibition of protein synthesis by binding to the 50S ribosomal subunit.
B. Disruption of the bacterial cytoplasmic membrane.
,C. Interference with DNA replication by inhibiting DNA gyrase.
D. Inhibition of peptidoglycan synthesis by binding to transpeptidase enzymes.
Correct Answer: D
Explanation: Beta-lactam antibiotics work by interfering with the synthesis of the
bacterial cell wall, specifically the cross-linking of peptidoglycan chains. They bind to
penicillin-binding proteins (PBPs), such as transpeptidase, which prevents the cell from
maintaining structural integrity. This leads to osmotic lysis and death of the bacterial cell.
4. Which of the following clinical signs are considered the cardinal signs of inflammation?
Select all that apply.
A. Redness (Rubor)
B. Heat (Calor)
C. Swelling (Tumor)
D. All of the above are cardinal signs.
E. Loss of function (Functio laesa)
F. Pain (Dolor)
Correct Answer: D
Explanation: The inflammatory response is characterized by five classic signs: redness,
heat, swelling, and pain, which were identified in ancient times. Loss of function was added
later as a fifth sign to reflect the impact on the affected tissue. These signs result from
increased blood flow, increased capillary permeability, and the recruitment of immune
cells to the site of injury.
5. A 5-year-old child presents with a ‘barking’ cough and inspiratory stridor. Which virus is the
most common cause of this condition, known as croup?
A. Parainfluenza virus
B. Respiratory Syncytial Virus (RSV)
C. Influenza A virus
D. Adenovirus
Correct Answer: A
Explanation: Croup, or laryngotracheobronchitis, is most frequently caused by
Parainfluenza viruses, particularly type 1. It is characterized by inflammation of the upper
airway, leading to the distinctive ‘seal-like’ barking cough. While RSV and Adenovirus can
cause respiratory symptoms, Parainfluenza is the classic etiologic agent for croup in
pediatric populations.
, 6. Which of the following describes the function of the enzyme reverse transcriptase in the
life cycle of HIV?
A. Cleaving large viral polyproteins into functional units.
B. Converting the viral RNA genome into a double-stranded DNA copy.
C. Integrating the viral genome into the host cell’s DNA.
D. Assisting in the attachment of the virus to the CD4 receptor.
Correct Answer: B
Explanation: Reverse transcriptase is an essential enzyme for retroviruses like HIV, as it
allows the conversion of single-stranded RNA into double-stranded DNA. This newly
synthesized DNA can then be transported into the nucleus and integrated into the host
genome. This step is a primary target for many antiretroviral therapies used to manage
HIV/AIDS.
7. Which organism is commonly associated with gastrointestinal infections following the
consumption of undercooked poultry or contaminated eggs?
A. Salmonella enterica
B. Shigella sonnei
C. Vibrio cholerae
D. Clostridium difficile
Correct Answer: A
Explanation: Salmonella enterica is a major cause of bacterial gastroenteritis worldwide,
often linked to poultry, eggs, and dairy products. The bacteria colonize the intestinal
epithelium, causing symptoms such as diarrhea, abdominal cramps, and fever. Proper food
handling and cooking are the most effective ways to prevent salmonellosis.
8. The Mantoux skin test is used to screen for exposure to which pathogen?
A. Staphylococcus aureus
B. Corynebacterium diphtheriae
C. Mycobacterium tuberculosis
D. Bordetella pertussis
Correct Answer: C
Explanation: The Mantoux test, also known as the PPD (Purified Protein Derivative) test,
screens for Mycobacterium tuberculosis infection. It relies on a Type IV delayed-type
hypersensitivity reaction, where an induration at the injection site indicates prior exposure
