BIOS 242 MICROBIOLOGY
COMPREHENSIVE FINAL EXAM
QUESTIONS AND ANSWERS
1. Which of the following components is found only in the cell walls of Gram-positive bacteria
and functions in cation transport and cell wall stability?
A. Lipopolysaccharide
B. Mycolic acid
C. Porins
D. Teichoic acids
Answer: D
Conceptual Explanation: Teichoic acids are found in the thick peptidoglycan layer of
Gram-positive bacteria. Lipopolysaccharides and porins are characteristic of Gram-
negative bacteria, while mycolic acid is found in Acid-fast bacteria.
2. During the process of aerobic respiration, which molecule serves as the final electron
acceptor in the electron transport chain?
A. Pyruvate
B. Oxygen (O2)
,C. NAD+
D. Sulfate
Answer: B
Conceptual Explanation: In aerobic respiration, oxygen is the final electron acceptor.
Pyruvate is an intermediate, NAD+ is an electron carrier, and sulfate is used in anaerobic
respiration by specific microbes.
3. Which mechanism of horizontal gene transfer involves the uptake of ‘naked’ DNA from the
surrounding environment by a competent cell?
A. Conjugation
B. Transformation
C. Transduction
D. Transposition
Answer: B
Conceptual Explanation: Transformation is the uptake of naked DNA. Conjugation
requires cell-to-cell contact via a pilus, and transduction involves a bacteriophage vector.
4. A mutation that results in the substitution of one amino acid for another in a protein
sequence is known as a:
A. Missense mutation
B. Silent mutation
, C. Nonsense mutation
D. Frameshift mutation
Answer: A
Conceptual Explanation: A missense mutation changes one amino acid. Silent mutations
do not change the amino acid, nonsense mutations create a premature stop codon, and
frameshift mutations shift the reading frame.
5. Which of the following immunoglobulins is the most abundant in serum and is the only
class capable of crossing the placenta to provide passive immunity to the fetus?
A. IgA
B. IgM
C. IgE
D. IgG
Answer: D
Conceptual Explanation: IgG is the most abundant serum antibody and the only one that
crosses the placenta. IgA is secreted in breast milk and mucosal surfaces, IgM is the first
responder, and IgE mediates allergic reactions.
6. The enzyme reverse transcriptase, found in retroviruses like HIV, performs which of the
following functions?
A. Synthesizes DNA from an RNA template
COMPREHENSIVE FINAL EXAM
QUESTIONS AND ANSWERS
1. Which of the following components is found only in the cell walls of Gram-positive bacteria
and functions in cation transport and cell wall stability?
A. Lipopolysaccharide
B. Mycolic acid
C. Porins
D. Teichoic acids
Answer: D
Conceptual Explanation: Teichoic acids are found in the thick peptidoglycan layer of
Gram-positive bacteria. Lipopolysaccharides and porins are characteristic of Gram-
negative bacteria, while mycolic acid is found in Acid-fast bacteria.
2. During the process of aerobic respiration, which molecule serves as the final electron
acceptor in the electron transport chain?
A. Pyruvate
B. Oxygen (O2)
,C. NAD+
D. Sulfate
Answer: B
Conceptual Explanation: In aerobic respiration, oxygen is the final electron acceptor.
Pyruvate is an intermediate, NAD+ is an electron carrier, and sulfate is used in anaerobic
respiration by specific microbes.
3. Which mechanism of horizontal gene transfer involves the uptake of ‘naked’ DNA from the
surrounding environment by a competent cell?
A. Conjugation
B. Transformation
C. Transduction
D. Transposition
Answer: B
Conceptual Explanation: Transformation is the uptake of naked DNA. Conjugation
requires cell-to-cell contact via a pilus, and transduction involves a bacteriophage vector.
4. A mutation that results in the substitution of one amino acid for another in a protein
sequence is known as a:
A. Missense mutation
B. Silent mutation
, C. Nonsense mutation
D. Frameshift mutation
Answer: A
Conceptual Explanation: A missense mutation changes one amino acid. Silent mutations
do not change the amino acid, nonsense mutations create a premature stop codon, and
frameshift mutations shift the reading frame.
5. Which of the following immunoglobulins is the most abundant in serum and is the only
class capable of crossing the placenta to provide passive immunity to the fetus?
A. IgA
B. IgM
C. IgE
D. IgG
Answer: D
Conceptual Explanation: IgG is the most abundant serum antibody and the only one that
crosses the placenta. IgA is secreted in breast milk and mucosal surfaces, IgM is the first
responder, and IgE mediates allergic reactions.
6. The enzyme reverse transcriptase, found in retroviruses like HIV, performs which of the
following functions?
A. Synthesizes DNA from an RNA template
