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BIOD 171 Module 5 Actual Exam 2026/2027 |
Essential Microbiology | Portage Learning |
Questions and Verified Answers | Pass
Guaranteed - A+ Graded
Section 1: Microbial Growth Requirements
Questions 1-8
Question 1 An organism that requires oxygen for growth but at lower concentrations than
atmospheric (2-10%) is called:
A. Obligate aerobe
B. Facultative anaerobe
C. Microaerophile [CORRECT]
D. Aerotolerant anaerobe
Correct Answer: C
Rationale: Microaerophiles require oxygen for metabolism but cannot tolerate atmospheric
concentrations (21%). They grow best at 2-10% oxygen, often found in environments like the
intestinal mucosa or soil microenvironments. Obligate aerobes (A) require full atmospheric
oxygen. Facultative anaerobes (B) can grow with or without oxygen but prefer it when available.
Aerotolerant anaerobes (D) do not use oxygen for metabolism but can tolerate its presence
through protective enzymes like superoxide dismutase.
Question 2 An organism that can grow in the presence or absence of oxygen but uses aerobic
respiration when oxygen is available is called:
A. Obligate aerobe
B. Facultative anaerobe [CORRECT]
C. Obligate anaerobe
D. Microaerophile
Correct Answer: B
,2
Rationale: Facultative anaerobes are metabolically flexible, switching between aerobic
respiration (with oxygen) and fermentation or anaerobic respiration (without oxygen). They grow
better with oxygen because aerobic respiration yields more ATP (36-38 ATP) compared to
fermentation (2 ATP). Examples include E. coli and Staphylococcus. Obligate aerobes (A) cannot
grow without oxygen. Obligate anaerobes (C) are killed by oxygen. Microaerophiles (D) require
reduced oxygen concentrations.
Question 3 Bacteria that thrive in high salt concentrations (15-30% NaCl) are called:
A. Acidophiles
B. Halophiles [CORRECT]
C. Thermophiles
D. Osmotolerant
Correct Answer: B
Rationale: Halophiles (salt-loving) require high salt concentrations for growth and structural
integrity, often found in salt lakes, evaporating ponds, and salted foods. Extreme halophiles like
Halobacterium require 15-30% NaCl. Acidophiles (A) thrive in acidic pH. Thermophiles (C)
thrive in high temperatures. Osmotolerant organisms (D) can survive osmotic stress but do not
require high salt for growth.
Question 4 An organism that grows optimally at human body temperature (37°C) would be
classified as:
A. Psychrophile
B. Mesophile [CORRECT]
C. Thermophile
D. Hyperthermophile
Correct Answer: B
Rationale: Mesophiles grow optimally at moderate temperatures (20-45°C), with most human
pathogens being mesophiles that grow best at 37°C. Their enzymes function optimally at these
temperatures. Psychrophiles (A) grow best below 15°C (cold environments). Thermophiles (C)
prefer 45-80°C (hot springs, compost). Hyperthermophiles (D) grow above 80°C (hydrothermal
vents).
Question 5 Which of the following correctly describes an obligate anaerobe?
, 3
A. Requires oxygen for growth and cannot grow without it
B. Can grow with or without oxygen but grows better with oxygen
C. Cannot grow in the presence of oxygen and may be killed by it [CORRECT]
D. Requires low concentrations of oxygen (2-10%) for growth
Correct Answer: C
Rationale: Obligate anaerobes lack superoxide dismutase (SOD), catalase, and peroxidase
enzymes that detoxify oxygen radicals (superoxide, hydrogen peroxide). Oxygen is toxic to
them, and they must be cultured in oxygen-free environments or reducing media. Clostridium
botulinum is a classic example. Option A describes obligate aerobes, B describes facultative
anaerobes, and D describes microaerophiles.
Question 6 Organisms that use carbon dioxide (CO₂) as their sole carbon source are called:
A. Heterotrophs
B. Autotrophs [CORRECT]
C. Chemotrophs
D. Organotrophs
Correct Answer: B
Rationale: Autotrophs ("self-feeders") fix CO₂ into organic compounds via Calvin cycle or other
carbon fixation pathways. They do not require organic carbon sources. Heterotrophs (A) require
organic carbon compounds. Chemotrophs (C) refers to energy source (chemical compounds), not
carbon source. Organotrophs (D) use organic compounds as electron donors.
Question 7 Nitrogen-fixing bacteria are important in microbiology because they:
A. Convert atmospheric N₂ to ammonia [CORRECT]
B. Convert ammonia to nitrate
C. Convert nitrate to nitrogen gas
D. Synthesize amino acids from carbohydrates
Correct Answer: A
Rationale: Nitrogen fixation is the biological conversion of atmospheric N₂ (unusable by most
organisms) into ammonia (NH₃), which can be incorporated into amino acids and nucleotides.
This process requires nitrogenase enzyme and is energetically expensive (16 ATP per N₂).
Examples include Rhizobium (symbiotic) and Azotobacter (free-living). Nitrification (B) is done
by nitrifying bacteria. Denitrification (C) converts nitrate to N₂.
BIOD 171 Module 5 Actual Exam 2026/2027 |
Essential Microbiology | Portage Learning |
Questions and Verified Answers | Pass
Guaranteed - A+ Graded
Section 1: Microbial Growth Requirements
Questions 1-8
Question 1 An organism that requires oxygen for growth but at lower concentrations than
atmospheric (2-10%) is called:
A. Obligate aerobe
B. Facultative anaerobe
C. Microaerophile [CORRECT]
D. Aerotolerant anaerobe
Correct Answer: C
Rationale: Microaerophiles require oxygen for metabolism but cannot tolerate atmospheric
concentrations (21%). They grow best at 2-10% oxygen, often found in environments like the
intestinal mucosa or soil microenvironments. Obligate aerobes (A) require full atmospheric
oxygen. Facultative anaerobes (B) can grow with or without oxygen but prefer it when available.
Aerotolerant anaerobes (D) do not use oxygen for metabolism but can tolerate its presence
through protective enzymes like superoxide dismutase.
Question 2 An organism that can grow in the presence or absence of oxygen but uses aerobic
respiration when oxygen is available is called:
A. Obligate aerobe
B. Facultative anaerobe [CORRECT]
C. Obligate anaerobe
D. Microaerophile
Correct Answer: B
,2
Rationale: Facultative anaerobes are metabolically flexible, switching between aerobic
respiration (with oxygen) and fermentation or anaerobic respiration (without oxygen). They grow
better with oxygen because aerobic respiration yields more ATP (36-38 ATP) compared to
fermentation (2 ATP). Examples include E. coli and Staphylococcus. Obligate aerobes (A) cannot
grow without oxygen. Obligate anaerobes (C) are killed by oxygen. Microaerophiles (D) require
reduced oxygen concentrations.
Question 3 Bacteria that thrive in high salt concentrations (15-30% NaCl) are called:
A. Acidophiles
B. Halophiles [CORRECT]
C. Thermophiles
D. Osmotolerant
Correct Answer: B
Rationale: Halophiles (salt-loving) require high salt concentrations for growth and structural
integrity, often found in salt lakes, evaporating ponds, and salted foods. Extreme halophiles like
Halobacterium require 15-30% NaCl. Acidophiles (A) thrive in acidic pH. Thermophiles (C)
thrive in high temperatures. Osmotolerant organisms (D) can survive osmotic stress but do not
require high salt for growth.
Question 4 An organism that grows optimally at human body temperature (37°C) would be
classified as:
A. Psychrophile
B. Mesophile [CORRECT]
C. Thermophile
D. Hyperthermophile
Correct Answer: B
Rationale: Mesophiles grow optimally at moderate temperatures (20-45°C), with most human
pathogens being mesophiles that grow best at 37°C. Their enzymes function optimally at these
temperatures. Psychrophiles (A) grow best below 15°C (cold environments). Thermophiles (C)
prefer 45-80°C (hot springs, compost). Hyperthermophiles (D) grow above 80°C (hydrothermal
vents).
Question 5 Which of the following correctly describes an obligate anaerobe?
, 3
A. Requires oxygen for growth and cannot grow without it
B. Can grow with or without oxygen but grows better with oxygen
C. Cannot grow in the presence of oxygen and may be killed by it [CORRECT]
D. Requires low concentrations of oxygen (2-10%) for growth
Correct Answer: C
Rationale: Obligate anaerobes lack superoxide dismutase (SOD), catalase, and peroxidase
enzymes that detoxify oxygen radicals (superoxide, hydrogen peroxide). Oxygen is toxic to
them, and they must be cultured in oxygen-free environments or reducing media. Clostridium
botulinum is a classic example. Option A describes obligate aerobes, B describes facultative
anaerobes, and D describes microaerophiles.
Question 6 Organisms that use carbon dioxide (CO₂) as their sole carbon source are called:
A. Heterotrophs
B. Autotrophs [CORRECT]
C. Chemotrophs
D. Organotrophs
Correct Answer: B
Rationale: Autotrophs ("self-feeders") fix CO₂ into organic compounds via Calvin cycle or other
carbon fixation pathways. They do not require organic carbon sources. Heterotrophs (A) require
organic carbon compounds. Chemotrophs (C) refers to energy source (chemical compounds), not
carbon source. Organotrophs (D) use organic compounds as electron donors.
Question 7 Nitrogen-fixing bacteria are important in microbiology because they:
A. Convert atmospheric N₂ to ammonia [CORRECT]
B. Convert ammonia to nitrate
C. Convert nitrate to nitrogen gas
D. Synthesize amino acids from carbohydrates
Correct Answer: A
Rationale: Nitrogen fixation is the biological conversion of atmospheric N₂ (unusable by most
organisms) into ammonia (NH₃), which can be incorporated into amino acids and nucleotides.
This process requires nitrogenase enzyme and is energetically expensive (16 ATP per N₂).
Examples include Rhizobium (symbiotic) and Azotobacter (free-living). Nitrification (B) is done
by nitrifying bacteria. Denitrification (C) converts nitrate to N₂.
