BIOD 171 Microbiology Module 4 – Latest Updated 2025–2026 | Cultivation,
Isolation, Identification & Microbial Control
1. Which answer best identifies or explains aseptic technique?
A. a technique that increases microbial contamination
B. practices that minimize contamination of cultures, personnel, and the environment
C. a method for sequencing genomes
D. a staining method only
Answer: B. practices that minimize contamination of cultures, personnel, and the environment
Rationale: Aseptic technique reduces unwanted microbial transfer and protects both cultures and
workers.
2. Which answer best identifies or explains a pure culture?
A. a culture containing a single microbial species or strain
B. a culture with many unrelated species
C. a viral capsid preparation
D. a sterile tube with no cells
Answer: A. a culture containing a single microbial species or strain
Rationale: Pure cultures allow reliable study and identification of one organism.
3. Which answer best identifies or explains an inoculum?
A. a staining mordant
B. a microscope objective
C. microbial material introduced into a culture medium
D. a chemical disinfectant
Answer: C. microbial material introduced into a culture medium
Rationale: The inoculum is the sample of microorganisms used to start a culture.
4. Which answer best identifies or explains a colony?
A. an antibiotic disk
B. a single viral genome
C. a visible mass of microbial cells arising from growth on solid medium, often from one progenitor
cell or cluster
D. a stain precipitate
Answer: C. a visible mass of microbial cells arising from growth on solid medium, often from one
progenitor cell or cluster
Rationale: Colonies on solid media represent localized microbial growth.
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,5. Which answer best identifies or explains a broth medium?
A. a liquid nutrient medium used to cultivate microorganisms
B. a solid medium containing agar only
C. a staining reagent
D. a sterilizing gas
Answer: A. a liquid nutrient medium used to cultivate microorganisms
Rationale: Broth supports microbial growth in liquid suspension.
6. Which answer best identifies or explains agar?
A. a universal nutrient source for every bacterium
B. a polysaccharide commonly used to solidify microbiological media
C. a bacterial toxin
D. a dye used in Gram staining
Answer: B. a polysaccharide commonly used to solidify microbiological media
Rationale: Agar forms a stable gel at incubation temperatures and is generally not metabolized by most
bacteria.
7. Which answer best identifies or explains a general-purpose medium?
A. a medium that selects one group only
B. a medium containing no nutrients
C. a medium designed to support growth of many nonfastidious organisms
D. a stain for endospores
Answer: C. a medium designed to support growth of many nonfastidious organisms
Rationale: General-purpose media supply basic nutrients without intentionally selecting or differentiating
particular groups.
8. Which answer best identifies or explains an enriched medium?
A. a sterilant
B. a general medium supplemented with additional nutrients such as blood or growth factors
C. a medium with no carbon source
D. a medium that contains only inhibitors
Answer: B. a general medium supplemented with additional nutrients such as blood or growth
factors
Rationale: Enriched media support fastidious organisms by providing extra nutrients.
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, 9. Which answer best identifies or explains a selective medium?
A. a completely nutrient-free medium
B. a medium that distinguishes organisms without affecting growth
C. a medium used only to magnify cells
D. a medium containing conditions or chemicals that inhibit some microbes while permitting others to
grow
Answer: D. a medium containing conditions or chemicals that inhibit some microbes while
permitting others to grow
Rationale: Selective media favor growth of particular groups by suppressing competitors.
10. Which answer best identifies or explains a differential medium?
A. a medium that reveals visible differences among organisms based on biochemical traits
B. a stain that fixes cells
C. a medium that always kills Gram-positive bacteria
D. a medium used only for viruses
Answer: A. a medium that reveals visible differences among organisms based on biochemical traits
Rationale: Differential media contain indicators that reveal differences such as fermentation or enzyme
activity.
11. Which answer best identifies or explains MacConkey agar?
A. a selective and differential medium commonly used for Gram-negative enteric bacteria and lactose
fermentation
B. a medium used specifically for fungal spores only
C. a stain for acid-fast cells
D. a universal anaerobic transport medium
Answer: A. a selective and differential medium commonly used for Gram-negative enteric bacteria
and lactose fermentation
Rationale: MacConkey inhibits many Gram-positive organisms and differentiates lactose fermenters by
colony color changes.
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Isolation, Identification & Microbial Control
1. Which answer best identifies or explains aseptic technique?
A. a technique that increases microbial contamination
B. practices that minimize contamination of cultures, personnel, and the environment
C. a method for sequencing genomes
D. a staining method only
Answer: B. practices that minimize contamination of cultures, personnel, and the environment
Rationale: Aseptic technique reduces unwanted microbial transfer and protects both cultures and
workers.
2. Which answer best identifies or explains a pure culture?
A. a culture containing a single microbial species or strain
B. a culture with many unrelated species
C. a viral capsid preparation
D. a sterile tube with no cells
Answer: A. a culture containing a single microbial species or strain
Rationale: Pure cultures allow reliable study and identification of one organism.
3. Which answer best identifies or explains an inoculum?
A. a staining mordant
B. a microscope objective
C. microbial material introduced into a culture medium
D. a chemical disinfectant
Answer: C. microbial material introduced into a culture medium
Rationale: The inoculum is the sample of microorganisms used to start a culture.
4. Which answer best identifies or explains a colony?
A. an antibiotic disk
B. a single viral genome
C. a visible mass of microbial cells arising from growth on solid medium, often from one progenitor
cell or cluster
D. a stain precipitate
Answer: C. a visible mass of microbial cells arising from growth on solid medium, often from one
progenitor cell or cluster
Rationale: Colonies on solid media represent localized microbial growth.
Page 1
,5. Which answer best identifies or explains a broth medium?
A. a liquid nutrient medium used to cultivate microorganisms
B. a solid medium containing agar only
C. a staining reagent
D. a sterilizing gas
Answer: A. a liquid nutrient medium used to cultivate microorganisms
Rationale: Broth supports microbial growth in liquid suspension.
6. Which answer best identifies or explains agar?
A. a universal nutrient source for every bacterium
B. a polysaccharide commonly used to solidify microbiological media
C. a bacterial toxin
D. a dye used in Gram staining
Answer: B. a polysaccharide commonly used to solidify microbiological media
Rationale: Agar forms a stable gel at incubation temperatures and is generally not metabolized by most
bacteria.
7. Which answer best identifies or explains a general-purpose medium?
A. a medium that selects one group only
B. a medium containing no nutrients
C. a medium designed to support growth of many nonfastidious organisms
D. a stain for endospores
Answer: C. a medium designed to support growth of many nonfastidious organisms
Rationale: General-purpose media supply basic nutrients without intentionally selecting or differentiating
particular groups.
8. Which answer best identifies or explains an enriched medium?
A. a sterilant
B. a general medium supplemented with additional nutrients such as blood or growth factors
C. a medium with no carbon source
D. a medium that contains only inhibitors
Answer: B. a general medium supplemented with additional nutrients such as blood or growth
factors
Rationale: Enriched media support fastidious organisms by providing extra nutrients.
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, 9. Which answer best identifies or explains a selective medium?
A. a completely nutrient-free medium
B. a medium that distinguishes organisms without affecting growth
C. a medium used only to magnify cells
D. a medium containing conditions or chemicals that inhibit some microbes while permitting others to
grow
Answer: D. a medium containing conditions or chemicals that inhibit some microbes while
permitting others to grow
Rationale: Selective media favor growth of particular groups by suppressing competitors.
10. Which answer best identifies or explains a differential medium?
A. a medium that reveals visible differences among organisms based on biochemical traits
B. a stain that fixes cells
C. a medium that always kills Gram-positive bacteria
D. a medium used only for viruses
Answer: A. a medium that reveals visible differences among organisms based on biochemical traits
Rationale: Differential media contain indicators that reveal differences such as fermentation or enzyme
activity.
11. Which answer best identifies or explains MacConkey agar?
A. a selective and differential medium commonly used for Gram-negative enteric bacteria and lactose
fermentation
B. a medium used specifically for fungal spores only
C. a stain for acid-fast cells
D. a universal anaerobic transport medium
Answer: A. a selective and differential medium commonly used for Gram-negative enteric bacteria
and lactose fermentation
Rationale: MacConkey inhibits many Gram-positive organisms and differentiates lactose fermenters by
colony color changes.
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