BIOL 271 Module 4 | Microbiology w/Lab Exam Q&A |
Portage Learning
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.
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, and temperatures above 45°C are typically lethal to most
mesophilic pathogens.
3. The bacterial growth curve phase in which cells are actively dividing at a constant,
maximum rate is the:
,A) Lag phase
B) Log phase
C) Stationary phase
D) Death phase
Correct Answer: Log phase
Rationale: The log (exponential) phase is characterized by rapid, constant cell
division where cells are at their most metabolically active. The generation time is at
its minimum during this phase. The lag phase is for adaptation, stationary phase
sees equal growth and death, and death phase is a decline in viable cells.
4. Obligate anaerobes are unable to grow in the presence of oxygen because they:
A) Require oxygen for growth
B) Use oxygen as a carbon source
C) Lack enzymes to detoxify reactive oxygen species
D) Are killed by low temperatures
Correct Answer: Lack enzymes to detoxify reactive oxygen species
Rationale: Obligate anaerobes lack enzymes such as catalase, superoxide
dismutase, and peroxidase that detoxify reactive oxygen species (ROS) like
superoxide and hydrogen peroxide. These ROS are produced during oxygen
metabolism and are lethal to organisms without protective enzymes.
5. Which type of growth medium contains inhibitors that suppress certain organisms
while allowing others to grow?
A) Universal medium
B) Selective medium
C) Differential medium
D) Enriched medium
,Correct Answer: Selective medium
Rationale: Selective media contain inhibitors such as antibiotics, salts, or dyes that
suppress the growth of unwanted organisms while allowing desired ones to grow.
Universal media support general growth, differential media distinguish based on
metabolic activity, and enriched media contain extra nutrients.
6. Universal growth media supports the growth of most:
A) Fastidious microorganisms
B) Non-fastidious microorganisms
C) Viruses
D) Obligate anaerobes
Correct Answer: Non-fastidious microorganisms
Rationale: Universal media like nutrient agar and tryptic soy agar contain basic
nutrients that support a wide range of non-fastidious bacteria. Fastidious organisms
require additional, specific nutrients found in enriched media.
7. MacConkey agar is both selective and differential. What does it select for?
A) Gram-positive bacteria
B) Gram-negative bacteria
C) Fungi
D) Viruses
Correct Answer: Gram-negative bacteria
Rationale: MacConkey agar contains bile salts and crystal violet, which inhibit the
growth of Gram-positive bacteria, making it selective for Gram-negative organisms. It
is differential because it distinguishes lactose fermenters (pink colonies) from non-
fermenters.
, 8. Blood agar is an example of a:
A) Selective medium
B) Enriched medium
C) Differential medium
D) Both B and C
Correct Answer: Both B and C
Rationale: Blood agar is an enriched medium because it contains blood, providing
additional nutrients for fastidious organisms. It is also a differential medium because
it differentiates bacteria based on hemolytic patterns (alpha, beta, and gamma
hemolysis).
9. Eosin Methylene Blue (EMB) agar is:
A) Only a selective medium
B) Only a differential medium
C) Both selective and differential
D) A universal medium
Correct Answer: Both selective and differential
Rationale: EMB agar is selective for Gram-negative bacteria due to the presence of
eosin and methylene blue dyes that inhibit Gram-positive organisms. It is differential
because lactose fermentation produces color changes in the colonies, distinguishing
fermenters from non-fermenters.
10. Mannitol salt agar (MSA) selects for which group of organisms?
A) Gram-negative bacteria
B) Halophiles
C) Acidophiles
D) Thermophiles
Portage Learning
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.
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, and temperatures above 45°C are typically lethal to most
mesophilic pathogens.
3. The bacterial growth curve phase in which cells are actively dividing at a constant,
maximum rate is the:
,A) Lag phase
B) Log phase
C) Stationary phase
D) Death phase
Correct Answer: Log phase
Rationale: The log (exponential) phase is characterized by rapid, constant cell
division where cells are at their most metabolically active. The generation time is at
its minimum during this phase. The lag phase is for adaptation, stationary phase
sees equal growth and death, and death phase is a decline in viable cells.
4. Obligate anaerobes are unable to grow in the presence of oxygen because they:
A) Require oxygen for growth
B) Use oxygen as a carbon source
C) Lack enzymes to detoxify reactive oxygen species
D) Are killed by low temperatures
Correct Answer: Lack enzymes to detoxify reactive oxygen species
Rationale: Obligate anaerobes lack enzymes such as catalase, superoxide
dismutase, and peroxidase that detoxify reactive oxygen species (ROS) like
superoxide and hydrogen peroxide. These ROS are produced during oxygen
metabolism and are lethal to organisms without protective enzymes.
5. Which type of growth medium contains inhibitors that suppress certain organisms
while allowing others to grow?
A) Universal medium
B) Selective medium
C) Differential medium
D) Enriched medium
,Correct Answer: Selective medium
Rationale: Selective media contain inhibitors such as antibiotics, salts, or dyes that
suppress the growth of unwanted organisms while allowing desired ones to grow.
Universal media support general growth, differential media distinguish based on
metabolic activity, and enriched media contain extra nutrients.
6. Universal growth media supports the growth of most:
A) Fastidious microorganisms
B) Non-fastidious microorganisms
C) Viruses
D) Obligate anaerobes
Correct Answer: Non-fastidious microorganisms
Rationale: Universal media like nutrient agar and tryptic soy agar contain basic
nutrients that support a wide range of non-fastidious bacteria. Fastidious organisms
require additional, specific nutrients found in enriched media.
7. MacConkey agar is both selective and differential. What does it select for?
A) Gram-positive bacteria
B) Gram-negative bacteria
C) Fungi
D) Viruses
Correct Answer: Gram-negative bacteria
Rationale: MacConkey agar contains bile salts and crystal violet, which inhibit the
growth of Gram-positive bacteria, making it selective for Gram-negative organisms. It
is differential because it distinguishes lactose fermenters (pink colonies) from non-
fermenters.
, 8. Blood agar is an example of a:
A) Selective medium
B) Enriched medium
C) Differential medium
D) Both B and C
Correct Answer: Both B and C
Rationale: Blood agar is an enriched medium because it contains blood, providing
additional nutrients for fastidious organisms. It is also a differential medium because
it differentiates bacteria based on hemolytic patterns (alpha, beta, and gamma
hemolysis).
9. Eosin Methylene Blue (EMB) agar is:
A) Only a selective medium
B) Only a differential medium
C) Both selective and differential
D) A universal medium
Correct Answer: Both selective and differential
Rationale: EMB agar is selective for Gram-negative bacteria due to the presence of
eosin and methylene blue dyes that inhibit Gram-positive organisms. It is differential
because lactose fermentation produces color changes in the colonies, distinguishing
fermenters from non-fermenters.
10. Mannitol salt agar (MSA) selects for which group of organisms?
A) Gram-negative bacteria
B) Halophiles
C) Acidophiles
D) Thermophiles
