,BIOL 271 Module 4 Exam | Microbiology w/ Lab |
Portage Learning | Q & A | 2026/2027 Edition
(PDF)
**1. Which of the following is considered a physical factor affecting microbial growth?**
A) Carbon source
B) Temperature
C) Nitrogen source
D) Oxygen
Correct Answer: Temperature
Rationale: Temperature is a physical factor that directly influences microbial growth by affecting enzyme
activity and membrane fluidity. Carbon, nitrogen, and oxygen are chemical factors that serve as
nutrients or energy sources. Physical factors also include pH and osmotic pressure, which are not
chemical in nature.
**2. Most human pathogens grow best at a temperature of approximately:**
A) 25°C
B) 37°C
C) 45°C
D) 60°C
Correct Answer: 37°C
Rationale: 37°C is normal human body temperature, which is optimal for most human pathogens. This
temperature supports the metabolic and growth requirements of organisms adapted to the human host.
25°C is often used to slow pathogen growth in laboratory settings, and temperatures above 45°C are
typically lethal to most mesophilic pathogens.
,**3. True or False: Researchers may incubate unknown bacterial samples at 25°C to restrict the growth
of pathogenic organisms.**
A) True
B) False
Correct Answer: True
Rationale: Incubating at 25°C (room temperature) rather than 37°C restricts the growth of many human
pathogens because they are adapted to the higher body temperature. This technique helps reduce the
risk of laboratory-acquired infections while still allowing non-pathogenic environmental organisms to
grow.
**4. The bacterial growth curve phase in which cells are adjusting to the environment and not yet
dividing is the:**
A) Log phase
B) Stationary phase
C) Lag phase
D) Death phase
Correct Answer: Lag phase
Rationale: During lag phase, cells are metabolically active but not yet dividing; they synthesize enzymes,
repair damage, and adapt to the new environment. Cell number remains relatively constant during this
phase. The duration of lag phase varies depending on the condition of the cells and the growth medium.
**5. The phase of most rapid cell division in a bacterial growth curve is the:**
A) Lag phase
B) Log (exponential) phase
C) Stationary phase
D) Death phase
, Correct Answer: Log (exponential) phase
Rationale: The log phase is characterized by rapid and constant cell division, with cells dividing at their
maximum rate. During this phase, the population doubles at regular intervals, and microbial metabolism
is most efficient, making it ideal for studying bacterial physiology and performing antibiotic susceptibility
testing.
**6. In the stationary phase of the bacterial growth curve, the rate of cell division is:**
A) Greater than the rate of cell death
B) Less than the rate of cell death
C) Equal to the rate of cell death
D) Zero
Correct Answer: Equal to the rate of cell death
Rationale: In stationary phase, the rate of cell division equals the rate of cell death, resulting in a stable
population size. This occurs when nutrients become depleted and waste products accumulate. Cells in
stationary phase may produce secondary metabolites, sporulate, or become more resistant to
environmental stresses.
**7. Generation time is defined as the time required for a population of cells to:**
A) Double in number
B) Triple in number
C) Increase tenfold
D) Decrease by half
Correct Answer: Double in number
Rationale: Generation time (also called doubling time) is the time required for a population of cells to
double in number during exponential growth. The generation time of E. coli under optimal conditions is
approximately 20 minutes, while some organisms may take hours or days to divide. This parameter is
essential for understanding microbial growth dynamics.
Portage Learning | Q & A | 2026/2027 Edition
(PDF)
**1. Which of the following is considered a physical factor affecting microbial growth?**
A) Carbon source
B) Temperature
C) Nitrogen source
D) Oxygen
Correct Answer: Temperature
Rationale: Temperature is a physical factor that directly influences microbial growth by affecting enzyme
activity and membrane fluidity. Carbon, nitrogen, and oxygen are chemical factors that serve as
nutrients or energy sources. Physical factors also include pH and osmotic pressure, which are not
chemical in nature.
**2. Most human pathogens grow best at a temperature of approximately:**
A) 25°C
B) 37°C
C) 45°C
D) 60°C
Correct Answer: 37°C
Rationale: 37°C is normal human body temperature, which is optimal for most human pathogens. This
temperature supports the metabolic and growth requirements of organisms adapted to the human host.
25°C is often used to slow pathogen growth in laboratory settings, and temperatures above 45°C are
typically lethal to most mesophilic pathogens.
,**3. True or False: Researchers may incubate unknown bacterial samples at 25°C to restrict the growth
of pathogenic organisms.**
A) True
B) False
Correct Answer: True
Rationale: Incubating at 25°C (room temperature) rather than 37°C restricts the growth of many human
pathogens because they are adapted to the higher body temperature. This technique helps reduce the
risk of laboratory-acquired infections while still allowing non-pathogenic environmental organisms to
grow.
**4. The bacterial growth curve phase in which cells are adjusting to the environment and not yet
dividing is the:**
A) Log phase
B) Stationary phase
C) Lag phase
D) Death phase
Correct Answer: Lag phase
Rationale: During lag phase, cells are metabolically active but not yet dividing; they synthesize enzymes,
repair damage, and adapt to the new environment. Cell number remains relatively constant during this
phase. The duration of lag phase varies depending on the condition of the cells and the growth medium.
**5. The phase of most rapid cell division in a bacterial growth curve is the:**
A) Lag phase
B) Log (exponential) phase
C) Stationary phase
D) Death phase
, Correct Answer: Log (exponential) phase
Rationale: The log phase is characterized by rapid and constant cell division, with cells dividing at their
maximum rate. During this phase, the population doubles at regular intervals, and microbial metabolism
is most efficient, making it ideal for studying bacterial physiology and performing antibiotic susceptibility
testing.
**6. In the stationary phase of the bacterial growth curve, the rate of cell division is:**
A) Greater than the rate of cell death
B) Less than the rate of cell death
C) Equal to the rate of cell death
D) Zero
Correct Answer: Equal to the rate of cell death
Rationale: In stationary phase, the rate of cell division equals the rate of cell death, resulting in a stable
population size. This occurs when nutrients become depleted and waste products accumulate. Cells in
stationary phase may produce secondary metabolites, sporulate, or become more resistant to
environmental stresses.
**7. Generation time is defined as the time required for a population of cells to:**
A) Double in number
B) Triple in number
C) Increase tenfold
D) Decrease by half
Correct Answer: Double in number
Rationale: Generation time (also called doubling time) is the time required for a population of cells to
double in number during exponential growth. The generation time of E. coli under optimal conditions is
approximately 20 minutes, while some organisms may take hours or days to divide. This parameter is
essential for understanding microbial growth dynamics.
