BIOD 171 Module 4 Exam – Microbiology (Portage Learning) (2026) Actual Questions with Verified Answers | Take & Pass the Exam

BIOD 171 Module 4 Exam – Microbiology (Portage Learning) (2026)
Actual Questions with Verified Answers | Take & Pass the Exam

Questions 1–120+


1. A researcher is asked to determine which of two vials contains E. coli and which contains
Salmonella. Knowing both are Gram-negative and only one can ferment lactose, which type of media
would be best suited?
A) Selective media
B) Differential media
C) Enriched media
D) Minimal media
Answer B: Differential media
Rationale: Differential media like MacConkey agar distinguishes lactose fermenters (E. coli, pink colonies)
from non-fermenters (Salmonella, colorless).




2. True or False: Differential media is best suited for distinguishing between two similar species of
bacteria.
A) True
B) False
Answer A: True
Rationale: Differential media contains indicators (e.g., pH dyes) that reveal metabolic differences between
similar organisms, allowing differentiation.




3. What is the primary component of a chromosome?
A) RNA
B) DNA
C) Protein
D) Lipid
Answer B: DNA

,Rationale: DNA carries the genetic information in chromosomes.




4. Which enzyme unwinds DNA during replication?
A) DNA polymerase
B) Helicase
C) Ligase
D) Primase
Answer B: Helicase
Rationale: Helicase breaks hydrogen bonds between DNA strands to unwind the double helix.




5. What is the role of DNA polymerase?
A) Unwinds DNA
B) Synthesizes new DNA
C) Seals nicks
D) Adds RNA primers
Answer B: Synthesizes new DNA
Rationale: DNA polymerase adds nucleotides to the growing DNA strand.




6. What is the function of ligase in DNA replication?
A) Unwinds DNA
B) Joins Okazaki fragments
C) Adds nucleotides
D) Removes primers
Answer B: Joins Okazaki fragments
Rationale: Ligase seals nicks in the lagging strand by joining Okazaki fragments.




7. What are the requirements of a fastidious microbe?
A) Only basic salts
B) Minimal media
C) Enriched media with specific growth factors
D) High salt concentration
Answer C: Enriched media with specific growth factors

,Rationale: Fastidious organisms need extra nutrients (e.g., blood, vitamins) absent in minimal media.




8. True or False: LB agar is classified as a selective, non-differential media.
A) True
B) False
Answer B: False
Rationale: LB agar is non-selective and non-differential; it supports broad bacterial growth without
restriction.




9. The polysaccharide-based hardening agent added to LB media to produce LB agar is derived from
what?
A) Bacterial cell wall
B) Corn starch
C) Seaweed (algae/agarose)
D) Synthetic polymers
Answer C: Seaweed (algae/agarose)
Rationale: Agar is extracted from red algae (seaweed) and solidifies culture media.




10. What is agar used for in microbiology?
A) As a nutrient source for bacteria
B) To inhibit bacterial growth
C) To provide a solid and even substrate for microbial growth
D) As a pH indicator
Answer C: To provide a solid and even substrate for microbial growth
Rationale: Agar is an inert polysaccharide used to solidify liquid media, creating a stable surface for colony
formation.




11. To differentiate E. coli (lactose fermenter) from Salmonella (non-fermenter), the best medium is:
A) Nutrient agar
B) MacConkey agar (differential)
C) Blood agar
D) Mannitol salt agar

, Answer B: MacConkey agar (differential)
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Rationale: MacConkey agar differentiates lactose fermenters (pink colonies) from non-fermenters
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j0 (colorless colonies). j0




12. Columbia CNA agar is most similar to which media?
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A) TSA/TYSAE Agar
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B) MacConkey Agar
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C) Blood Agar (BAP)
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D) EMB Agar
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Answer C: Blood Agar (BAP)
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Rationale: CNA contains blood and antibiotics; like Blood Agar, it is enriched and differential for
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j0 hemolysis.




13. True or False: Chocolate agar gets its brown color from cocoa to produce an enriched media.
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B) False
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Answer B: False j0 j0




Rationale: Chocolate agar contains lysed red blood cells, giving a brown color—cocoa is never added.
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14. Blood agar is classified as: (Select all that apply)
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A) Selective
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B) Enriched
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C) Differential
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D) Inhibitory
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Answer B: Enriched, C: Differential
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Rationale: Blood agar supports fastidious organisms (enriched) and shows hemolysis patterns
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j0 (differential).




15. Match the following hemolytic class with its description: A. Alpha hemolysis B. Beta hemolysis
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