QUESTIONS AND CORRECT VERIFIED ANSWERS
FOR BIOL 271 MICROBIOLOGY EXAM 2026
1. Which scientist is credited with disproving spontaneous generation through the swan-
neck flask experiment?
A. Robert Koch
B. Louis Pasteur
C. Joseph Lister
D. Edward Jenner
Correct Answer: B
Explanation: Louis Pasteur's swan-neck flask experiment demonstrated that
microorganisms come from existing microorganisms rather than arising spontaneously.
Koch established germ theory, Jenner developed vaccination, and Lister pioneered
antiseptic surgery.
2. Which structure is primarily responsible for bacterial motility?
A. Capsule
B. Pili
C. Flagellum
D. Ribosome
Correct Answer: C
Explanation: Flagella provide motility through rotational movement. Capsules aid in
protection, pili assist in attachment and conjugation, and ribosomes are involved in
protein synthesis.
3. Which bacterial cell wall component is unique to Gram-positive bacteria?
A. Lipopolysaccharide
B. Outer membrane
C. Teichoic acid
D. Porin proteins
Correct Answer: C
Explanation: Teichoic acids are found only in Gram-positive cell walls. Gram-negative
bacteria possess lipopolysaccharides, porins, and an outer membrane.
4. During Gram staining, Gram-positive bacteria appear purple because they:
A. Absorb safranin strongly
B. Retain the crystal violet-iodine complex
C. Possess an outer membrane
D. Produce endospores
, Correct Answer: B
Explanation: Thick peptidoglycan layers in Gram-positive bacteria retain the crystal
violet-iodine complex after alcohol decolorization.
5. Which microbial growth phase is characterized by rapid cell division?
A. Lag phase
B. Death phase
C. Log phase
D. Stationary phase
Correct Answer: C
Explanation: The log (exponential) phase is marked by maximum growth and cell
division. Lag phase involves adaptation, stationary phase balances growth and death,
and death phase involves declining populations.
6. Which enzyme synthesizes DNA during bacterial replication?
A. DNA ligase
B. DNA polymerase III
C. Helicase
D. Primase
Correct Answer: B
Explanation: DNA polymerase III is the primary enzyme responsible for DNA synthesis
in bacteria. Helicase unwinds DNA, primase synthesizes RNA primers, and ligase joins
DNA fragments.
7. A microbiologist discovers a bacterium lacking a cell wall. Which antibiotic would likely
be ineffective?
A. Tetracycline
B. Penicillin
C. Chloramphenicol
D. Streptomycin
Correct Answer: B
Explanation: Penicillin targets peptidoglycan synthesis in bacterial cell walls. Without a
cell wall, the bacterium would be resistant to penicillin's mechanism of action.
8. Which type of microorganism is classified as a prokaryote?
A. Protozoan
B. Fungus
C. Bacterium
, D. Alga
Correct Answer: C
Explanation: Bacteria are prokaryotes because they lack a membrane-bound nucleus and
organelles. Protozoa, fungi, and algae are eukaryotic organisms.
9. What is the primary function of bacterial capsules?
A. ATP production
B. Protein synthesis
C. Protection against phagocytosis
D. DNA replication
Correct Answer: C
Explanation: Capsules protect bacteria from immune defenses such as phagocytosis and
help with adherence to surfaces.
10. Which process allows bacteria to exchange genetic material through direct contact?
A. Transformation
B. Transduction
C. Conjugation
D. Binary fission
Correct Answer: C
Explanation: Conjugation involves transfer of DNA via a pilus between bacterial cells.
Transformation involves uptake of naked DNA, while transduction uses bacteriophages.
11. Which structure is found in both prokaryotic and eukaryotic cells?
A. Nucleus
B. Mitochondrion
C. Ribosome
D. Golgi apparatus
Correct Answer: C
Explanation: Ribosomes are present in all cells and are responsible for protein synthesis.
12. Which type of media supports the growth of most microorganisms?
A. Differential media
B. Selective media
C. General-purpose media
D. Enrichment media
Correct Answer: C
FOR BIOL 271 MICROBIOLOGY EXAM 2026
1. Which scientist is credited with disproving spontaneous generation through the swan-
neck flask experiment?
A. Robert Koch
B. Louis Pasteur
C. Joseph Lister
D. Edward Jenner
Correct Answer: B
Explanation: Louis Pasteur's swan-neck flask experiment demonstrated that
microorganisms come from existing microorganisms rather than arising spontaneously.
Koch established germ theory, Jenner developed vaccination, and Lister pioneered
antiseptic surgery.
2. Which structure is primarily responsible for bacterial motility?
A. Capsule
B. Pili
C. Flagellum
D. Ribosome
Correct Answer: C
Explanation: Flagella provide motility through rotational movement. Capsules aid in
protection, pili assist in attachment and conjugation, and ribosomes are involved in
protein synthesis.
3. Which bacterial cell wall component is unique to Gram-positive bacteria?
A. Lipopolysaccharide
B. Outer membrane
C. Teichoic acid
D. Porin proteins
Correct Answer: C
Explanation: Teichoic acids are found only in Gram-positive cell walls. Gram-negative
bacteria possess lipopolysaccharides, porins, and an outer membrane.
4. During Gram staining, Gram-positive bacteria appear purple because they:
A. Absorb safranin strongly
B. Retain the crystal violet-iodine complex
C. Possess an outer membrane
D. Produce endospores
, Correct Answer: B
Explanation: Thick peptidoglycan layers in Gram-positive bacteria retain the crystal
violet-iodine complex after alcohol decolorization.
5. Which microbial growth phase is characterized by rapid cell division?
A. Lag phase
B. Death phase
C. Log phase
D. Stationary phase
Correct Answer: C
Explanation: The log (exponential) phase is marked by maximum growth and cell
division. Lag phase involves adaptation, stationary phase balances growth and death,
and death phase involves declining populations.
6. Which enzyme synthesizes DNA during bacterial replication?
A. DNA ligase
B. DNA polymerase III
C. Helicase
D. Primase
Correct Answer: B
Explanation: DNA polymerase III is the primary enzyme responsible for DNA synthesis
in bacteria. Helicase unwinds DNA, primase synthesizes RNA primers, and ligase joins
DNA fragments.
7. A microbiologist discovers a bacterium lacking a cell wall. Which antibiotic would likely
be ineffective?
A. Tetracycline
B. Penicillin
C. Chloramphenicol
D. Streptomycin
Correct Answer: B
Explanation: Penicillin targets peptidoglycan synthesis in bacterial cell walls. Without a
cell wall, the bacterium would be resistant to penicillin's mechanism of action.
8. Which type of microorganism is classified as a prokaryote?
A. Protozoan
B. Fungus
C. Bacterium
, D. Alga
Correct Answer: C
Explanation: Bacteria are prokaryotes because they lack a membrane-bound nucleus and
organelles. Protozoa, fungi, and algae are eukaryotic organisms.
9. What is the primary function of bacterial capsules?
A. ATP production
B. Protein synthesis
C. Protection against phagocytosis
D. DNA replication
Correct Answer: C
Explanation: Capsules protect bacteria from immune defenses such as phagocytosis and
help with adherence to surfaces.
10. Which process allows bacteria to exchange genetic material through direct contact?
A. Transformation
B. Transduction
C. Conjugation
D. Binary fission
Correct Answer: C
Explanation: Conjugation involves transfer of DNA via a pilus between bacterial cells.
Transformation involves uptake of naked DNA, while transduction uses bacteriophages.
11. Which structure is found in both prokaryotic and eukaryotic cells?
A. Nucleus
B. Mitochondrion
C. Ribosome
D. Golgi apparatus
Correct Answer: C
Explanation: Ribosomes are present in all cells and are responsible for protein synthesis.
12. Which type of media supports the growth of most microorganisms?
A. Differential media
B. Selective media
C. General-purpose media
D. Enrichment media
Correct Answer: C
