Below is a set of revision test questions—each with answer choices and an explanation (rationale)—
designed to help you review key concepts found in Benson's Microbiological Applications Laboratory
Manual, 15th Edition by Heidi Smith. You can use these questions to self-assess your understanding of
lab procedures, safety, and the theoretical basis behind common microbiological techniques
Revision Test Questions with Rationale
Question 1: Aseptic Technique
Q: What is the primary purpose of aseptic technique in the microbiology laboratory?
Options:
A) To enhance microbial growth
B) To prevent contamination of samples and the environment
C) To encourage the mixing of different microbial species
D) To expedite the sterilization process
Correct Answer: B
Rationale:
Aseptic technique is essential for keeping samples free of extraneous microorganisms. This minimizes
cross-contamination and ensures that experimental results are accurate and reproducible.
Question 2: Bunsen Burner Use
Q: What is the primary function of the Bunsen burner in microbiology labs?
Options:
A) To sterilize the lab bench surface
B) To generate an updraft that prevents airborne contamination during manipulations
C) To cook samples for microbial analysis
D) To dry culture plates
Correct Answer: B
Rationale:
The flame from a Bunsen burner creates a convection current (updraft) that minimizes the chance of
airborne contaminants settling on sterile instruments or culture media during procedures.
Question 3: Culture Media Characteristics
Q: Which of the following media is both selective and differential for Gram-negative bacteria?
Options:
A) Blood Agar
B) MacConkey Agar
C) Nutrient Agar
D) Sabouraud Dextrose Agar
, Correct Answer: B
Rationale:
MacConkey agar contains bile salts and crystal violet, which inhibit Gram-positive bacteria (selective),
and differentiates between lactose fermenters and non-fermenters (differential), making it ideal for
isolating Gram-negative organisms.
Question 4: Gram Staining Process
Q: During the Gram staining procedure, what is the purpose of applying iodine after crystal violet?
Options:
A) To fix the crystal violet stain inside the cell
B) To decolorize the bacterial cell wall
C) To counterstain the bacteria red
D) To act as a mordant enhancing the stain's retention
Correct Answer: D
Rationale:
Iodine functions as a mordant; it forms a complex with the crystal violet dye that becomes trapped in
the thick peptidoglycan layer of Gram-positive bacteria, ensuring that these cells retain the primary
stain.
Question 5: Sterilization Methods
Q: Which of the following is the most effective method for sterilizing heat-resistant laboratory
equipment?
Options:
A) Autoclaving
B) Dry heat sterilization
C) Filtration
D) Chemical disinfection
Correct Answer: A
Rationale:
Autoclaving uses pressurized steam at around 121°C, which efficiently destroys all microorganisms,
including spores. This method is preferred for sterilizing equipment that can withstand high
temperatures.
Question 6: Inoculation Techniques
Q: When performing a streak plate technique, what is the primary goal?
Options:
A) To create a uniform mixture of bacteria
designed to help you review key concepts found in Benson's Microbiological Applications Laboratory
Manual, 15th Edition by Heidi Smith. You can use these questions to self-assess your understanding of
lab procedures, safety, and the theoretical basis behind common microbiological techniques
Revision Test Questions with Rationale
Question 1: Aseptic Technique
Q: What is the primary purpose of aseptic technique in the microbiology laboratory?
Options:
A) To enhance microbial growth
B) To prevent contamination of samples and the environment
C) To encourage the mixing of different microbial species
D) To expedite the sterilization process
Correct Answer: B
Rationale:
Aseptic technique is essential for keeping samples free of extraneous microorganisms. This minimizes
cross-contamination and ensures that experimental results are accurate and reproducible.
Question 2: Bunsen Burner Use
Q: What is the primary function of the Bunsen burner in microbiology labs?
Options:
A) To sterilize the lab bench surface
B) To generate an updraft that prevents airborne contamination during manipulations
C) To cook samples for microbial analysis
D) To dry culture plates
Correct Answer: B
Rationale:
The flame from a Bunsen burner creates a convection current (updraft) that minimizes the chance of
airborne contaminants settling on sterile instruments or culture media during procedures.
Question 3: Culture Media Characteristics
Q: Which of the following media is both selective and differential for Gram-negative bacteria?
Options:
A) Blood Agar
B) MacConkey Agar
C) Nutrient Agar
D) Sabouraud Dextrose Agar
, Correct Answer: B
Rationale:
MacConkey agar contains bile salts and crystal violet, which inhibit Gram-positive bacteria (selective),
and differentiates between lactose fermenters and non-fermenters (differential), making it ideal for
isolating Gram-negative organisms.
Question 4: Gram Staining Process
Q: During the Gram staining procedure, what is the purpose of applying iodine after crystal violet?
Options:
A) To fix the crystal violet stain inside the cell
B) To decolorize the bacterial cell wall
C) To counterstain the bacteria red
D) To act as a mordant enhancing the stain's retention
Correct Answer: D
Rationale:
Iodine functions as a mordant; it forms a complex with the crystal violet dye that becomes trapped in
the thick peptidoglycan layer of Gram-positive bacteria, ensuring that these cells retain the primary
stain.
Question 5: Sterilization Methods
Q: Which of the following is the most effective method for sterilizing heat-resistant laboratory
equipment?
Options:
A) Autoclaving
B) Dry heat sterilization
C) Filtration
D) Chemical disinfection
Correct Answer: A
Rationale:
Autoclaving uses pressurized steam at around 121°C, which efficiently destroys all microorganisms,
including spores. This method is preferred for sterilizing equipment that can withstand high
temperatures.
Question 6: Inoculation Techniques
Q: When performing a streak plate technique, what is the primary goal?
Options:
A) To create a uniform mixture of bacteria
