PORTAGE LEARNING
Microbiology — BIOL 271 / BIOL 271
BIOL 271 Module 4: Growth Media & Cultivation 2026/2027
Comprehensive Question Bank
Module 4 Review
Question 1
Which of the following is a chemoheterotroph?
A. Plants
B. Algae
C. Fungi
D. Sulfur bacteria
Correct Answer C. Fungi
Rationale:
Fungi obtain both energy and carbon from organic compounds, making them chemoheterotrophs.
Question 2
Why is chocolate agar enriched?
A. It contains antibiotics to kill unwanted bacteria
B. Lysed RBCs release growth factors for fastidious organisms
C. It contains high salt concentration
D. It contains lactose and a pH indicator
Correct Answer B. Lysed RBCs release growth factors for fastidious organisms
Rationale:
Heating lyses red blood cells, releasing hemin (X factor) and NAD (V factor), which are essential for
the growth of fastidious organisms like Haemophilus influenzae.
, Question 3
Is MacConkey selective?
A. Yes
B. No
C. Only for Gram-positive bacteria
D. Only for fastidious organisms
Correct Answer A. Yes
Rationale:
MacConkey agar is selective because it contains crystal violet and bile salts that inhibit Gram-positive
bacteria, allowing Gram-negative organisms to grow.
Question 4
What is a pure culture?
A. A culture containing multiple microorganisms
B. A culture containing only one microorganism
C. A culture grown in liquid media
D. A culture that is free of contaminants
Correct Answer B. A culture containing only one microorganism
Rationale:
A pure culture contains a single microbial species, enabling accurate study of its properties without
interference from other organisms.
Question 5
What color are lactose fermenters on MacConkey?
A. White
B. Yellow
C. Pink/red
D. Green
Correct Answer C. Pink/red
Rationale:
Lactose fermenters produce acid, lowering the pH and turning the neutral red indicator pink/red (e.g.,
E. coli, Klebsiella).
, Question 6
What is LB broth?
A. A selective medium for Gram-negative bacteria
B. A nutrient-rich liquid media that grows many types of bacteria
C. A differential medium for lactose fermenters
D. A solid medium used for fungal culture
Correct Answer B. A nutrient-rich liquid media that grows many types of bacteria
Rationale:
LB broth (Lysogeny Broth) is a rich, non-selective liquid medium that supports the growth of many
different microbial species, making it a staple in molecular biology.
Question 7
What is alpha hemolysis?
A. Complete RBC lysis producing a clear zone
B. Partial RBC lysis producing a greenish-brown color
C. No RBC lysis
D. Lysis of white blood cells only
Correct Answer B. Partial RBC lysis producing a greenish-brown color
Rationale:
Alpha hemolysis results in a green/brown zone around colonies due to the partial breakdown of
hemoglobin to methemoglobin, characteristic of organisms like Streptococcus pneumoniae.
Question 8
What type of bacteria does CNA select for?
A. Gram-negative bacteria
B. Gram-positive bacteria
C. Fungi
D. Viruses
Correct Answer B. Gram-positive bacteria
Rationale:
CNA agar contains colistin and nalidixic acid, which inhibit Gram-negative bacteria, allowing Gram-
positive organisms to grow selectively.
Microbiology — BIOL 271 / BIOL 271
BIOL 271 Module 4: Growth Media & Cultivation 2026/2027
Comprehensive Question Bank
Module 4 Review
Question 1
Which of the following is a chemoheterotroph?
A. Plants
B. Algae
C. Fungi
D. Sulfur bacteria
Correct Answer C. Fungi
Rationale:
Fungi obtain both energy and carbon from organic compounds, making them chemoheterotrophs.
Question 2
Why is chocolate agar enriched?
A. It contains antibiotics to kill unwanted bacteria
B. Lysed RBCs release growth factors for fastidious organisms
C. It contains high salt concentration
D. It contains lactose and a pH indicator
Correct Answer B. Lysed RBCs release growth factors for fastidious organisms
Rationale:
Heating lyses red blood cells, releasing hemin (X factor) and NAD (V factor), which are essential for
the growth of fastidious organisms like Haemophilus influenzae.
, Question 3
Is MacConkey selective?
A. Yes
B. No
C. Only for Gram-positive bacteria
D. Only for fastidious organisms
Correct Answer A. Yes
Rationale:
MacConkey agar is selective because it contains crystal violet and bile salts that inhibit Gram-positive
bacteria, allowing Gram-negative organisms to grow.
Question 4
What is a pure culture?
A. A culture containing multiple microorganisms
B. A culture containing only one microorganism
C. A culture grown in liquid media
D. A culture that is free of contaminants
Correct Answer B. A culture containing only one microorganism
Rationale:
A pure culture contains a single microbial species, enabling accurate study of its properties without
interference from other organisms.
Question 5
What color are lactose fermenters on MacConkey?
A. White
B. Yellow
C. Pink/red
D. Green
Correct Answer C. Pink/red
Rationale:
Lactose fermenters produce acid, lowering the pH and turning the neutral red indicator pink/red (e.g.,
E. coli, Klebsiella).
, Question 6
What is LB broth?
A. A selective medium for Gram-negative bacteria
B. A nutrient-rich liquid media that grows many types of bacteria
C. A differential medium for lactose fermenters
D. A solid medium used for fungal culture
Correct Answer B. A nutrient-rich liquid media that grows many types of bacteria
Rationale:
LB broth (Lysogeny Broth) is a rich, non-selective liquid medium that supports the growth of many
different microbial species, making it a staple in molecular biology.
Question 7
What is alpha hemolysis?
A. Complete RBC lysis producing a clear zone
B. Partial RBC lysis producing a greenish-brown color
C. No RBC lysis
D. Lysis of white blood cells only
Correct Answer B. Partial RBC lysis producing a greenish-brown color
Rationale:
Alpha hemolysis results in a green/brown zone around colonies due to the partial breakdown of
hemoglobin to methemoglobin, characteristic of organisms like Streptococcus pneumoniae.
Question 8
What type of bacteria does CNA select for?
A. Gram-negative bacteria
B. Gram-positive bacteria
C. Fungi
D. Viruses
Correct Answer B. Gram-positive bacteria
Rationale:
CNA agar contains colistin and nalidixic acid, which inhibit Gram-negative bacteria, allowing Gram-
positive organisms to grow selectively.
