Microbiology BIOD 171 Module 2 Exam Microbial
Growth Metabolism Genetics Control Actual Exam
2026/2027 – Portage Learning – Complete
Questions and Answers with Detailed Rationales –
Pass Guaranteed – A+ Graded
==================================================
PART A: Microbial Growth Requirements & Bacterial Reproduction
(12 Questions)
Q1: A bacterial culture isolated from a hot spring in Yellowstone National Park grows
optimally at 75°C but cannot grow below 60°C. How should this organism be classified?
A. Psychrophile
B. Mesophile
C. Thermophile [CORRECT]
D. Facultative psychrophile
Correct Answer: C
Rationale: Thermophiles grow optimally between 50-80°C, matching the hot spring
habitat and 75°C optimum described. Psychrophiles (A) prefer cold (<15°C), while
mesophiles (B) prefer moderate temperatures (20-45°C) like human pathogens.
"Facultative psychrophile" (D) is not standard terminology; psychrophiles are typically
,obligate. Portage Tip: Remember temperature ranges—psychro (cold), meso (middle),
thermo (heat), hyperthermo (extreme heat >80°C).
Q2 (Generation Time Math): Escherichia coli has a generation time of 20 minutes under
optimal conditions. If a culture starts with 5 × 10³ cells/mL, how many cells will be
present after 2 hours of exponential growth?
A. 5 × 10⁴ cells/mL
B. 1.6 × 10⁵ cells/mL
C. 3.2 × 10⁵ cells/mL [CORRECT]
D. 6.4 × 10⁶ cells/mL
Correct Answer: C
Rationale: Formula: Nt = N0 × 2ⁿ where n = total time ÷ generation time = 120 min ÷ 20
min = 6 generations. Calculation: 5 × 10³ × 2⁶ = 5 × 10³ × 64 = 320 × 10³ = 3.2 × 10⁵
cells/mL. Option A represents only 3.3 generations (1 log increase). Option D incorrectly
calculates 2⁷ (7 generations). Portage Tip: Always calculate n first, then apply the
exponent before multiplying by initial population.
Q3 (SATA): Which of the following microorganisms would be classified as obligate
anaerobes? (Select all that apply.)
A. Clostridium botulinum [CORRECT]
B. Mycobacterium tuberculosis
C. Bacteroides fragilis [CORRECT]
D. Staphylococcus aureus
E. Clostridium tetani [CORRECT]
F. Pseudomonas aeruginosa
, Correct Answer: A, C, E
Rationale: Obligate anaerobes cannot grow in oxygen and include Clostridium species
(A, E) and Bacteroides (C), which lack superoxide dismutase and catalase. M.
tuberculosis (B) and P. aeruginosa (F) are obligate aerobes requiring oxygen. S. aureus
(D) is a facultative anaerobe capable of fermentative or respiratory metabolism. Portage
Tip: Remember Clostridia (tetani, botulinum, perfringens) are classic obligate anaerobes
found in soil and anaerobic wounds.
Q4: During which phase of the bacterial growth curve are cells most susceptible to
antibiotics that target cell wall synthesis (such as penicillin)?
A. Lag phase
B. Log (exponential) phase [CORRECT]
C. Stationary phase
D. Death phase
Correct Answer: B
Rationale: The log phase is characterized by rapid binary fission and active
peptidoglycan synthesis, making cells most vulnerable to beta-lactam antibiotics that
inhibit cell wall formation. Lag phase (A) involves metabolic preparation without
division; stationary phase (C) involves slowed metabolism and spore formation; death
phase (D) involves cell lysis but antibiotics are less effective against dormant cells.
Portage Tip: "Log = susceptible, Stationary = resistant" is the rule for antibiotic
susceptibility testing.
Q5: A bacterium isolated from a lemon juice factory (pH 2.5) grows optimally at pH 3.0
but cannot grow above pH 6.0. This organism is best described as:
A. Neutrophile
Growth Metabolism Genetics Control Actual Exam
2026/2027 – Portage Learning – Complete
Questions and Answers with Detailed Rationales –
Pass Guaranteed – A+ Graded
==================================================
PART A: Microbial Growth Requirements & Bacterial Reproduction
(12 Questions)
Q1: A bacterial culture isolated from a hot spring in Yellowstone National Park grows
optimally at 75°C but cannot grow below 60°C. How should this organism be classified?
A. Psychrophile
B. Mesophile
C. Thermophile [CORRECT]
D. Facultative psychrophile
Correct Answer: C
Rationale: Thermophiles grow optimally between 50-80°C, matching the hot spring
habitat and 75°C optimum described. Psychrophiles (A) prefer cold (<15°C), while
mesophiles (B) prefer moderate temperatures (20-45°C) like human pathogens.
"Facultative psychrophile" (D) is not standard terminology; psychrophiles are typically
,obligate. Portage Tip: Remember temperature ranges—psychro (cold), meso (middle),
thermo (heat), hyperthermo (extreme heat >80°C).
Q2 (Generation Time Math): Escherichia coli has a generation time of 20 minutes under
optimal conditions. If a culture starts with 5 × 10³ cells/mL, how many cells will be
present after 2 hours of exponential growth?
A. 5 × 10⁴ cells/mL
B. 1.6 × 10⁵ cells/mL
C. 3.2 × 10⁵ cells/mL [CORRECT]
D. 6.4 × 10⁶ cells/mL
Correct Answer: C
Rationale: Formula: Nt = N0 × 2ⁿ where n = total time ÷ generation time = 120 min ÷ 20
min = 6 generations. Calculation: 5 × 10³ × 2⁶ = 5 × 10³ × 64 = 320 × 10³ = 3.2 × 10⁵
cells/mL. Option A represents only 3.3 generations (1 log increase). Option D incorrectly
calculates 2⁷ (7 generations). Portage Tip: Always calculate n first, then apply the
exponent before multiplying by initial population.
Q3 (SATA): Which of the following microorganisms would be classified as obligate
anaerobes? (Select all that apply.)
A. Clostridium botulinum [CORRECT]
B. Mycobacterium tuberculosis
C. Bacteroides fragilis [CORRECT]
D. Staphylococcus aureus
E. Clostridium tetani [CORRECT]
F. Pseudomonas aeruginosa
, Correct Answer: A, C, E
Rationale: Obligate anaerobes cannot grow in oxygen and include Clostridium species
(A, E) and Bacteroides (C), which lack superoxide dismutase and catalase. M.
tuberculosis (B) and P. aeruginosa (F) are obligate aerobes requiring oxygen. S. aureus
(D) is a facultative anaerobe capable of fermentative or respiratory metabolism. Portage
Tip: Remember Clostridia (tetani, botulinum, perfringens) are classic obligate anaerobes
found in soil and anaerobic wounds.
Q4: During which phase of the bacterial growth curve are cells most susceptible to
antibiotics that target cell wall synthesis (such as penicillin)?
A. Lag phase
B. Log (exponential) phase [CORRECT]
C. Stationary phase
D. Death phase
Correct Answer: B
Rationale: The log phase is characterized by rapid binary fission and active
peptidoglycan synthesis, making cells most vulnerable to beta-lactam antibiotics that
inhibit cell wall formation. Lag phase (A) involves metabolic preparation without
division; stationary phase (C) involves slowed metabolism and spore formation; death
phase (D) involves cell lysis but antibiotics are less effective against dormant cells.
Portage Tip: "Log = susceptible, Stationary = resistant" is the rule for antibiotic
susceptibility testing.
Q5: A bacterium isolated from a lemon juice factory (pH 2.5) grows optimally at pH 3.0
but cannot grow above pH 6.0. This organism is best described as:
A. Neutrophile
