Microbiology Lab Practical 1 (Pearson
Education Edition) Questions and
Answers 100% Pass
What is the purpose of staining bacterial cells?
✔✔ To increase contrast and make the cells visible under a microscope.
What is the primary dye used in Gram staining?
✔✔ Crystal violet.
Why is iodine used in Gram staining?
✔✔ It acts as a mordant to form a complex with the crystal violet, making it adhere better to the
bacterial cell walls.
What color do Gram-positive bacteria appear after staining?
✔✔ Purple.
What color do Gram-negative bacteria appear after staining?
✔✔ Pink or red.
1
,Why is heat fixation performed before staining a bacterial smear?
✔✔ To kill the bacteria and fix them to the slide.
What is the main difference between Gram-positive and Gram-negative bacterial cell walls?
✔✔ Gram-positive bacteria have a thick peptidoglycan layer, while Gram-negative bacteria have
a thin peptidoglycan layer and an outer membrane.
What is the purpose of using safranin in the Gram stain procedure?
✔✔ It is a counterstain that colors Gram-negative bacteria pink.
What is the shape of cocci bacteria?
✔✔ Spherical.
What is the shape of bacilli bacteria?
✔✔ Rod-shaped.
What is the function of the condenser on a microscope?
2
,✔✔ To focus light onto the specimen.
Why is oil immersion used with the 100x objective lens?
✔✔ To reduce light refraction and increase resolution.
What is the purpose of the aseptic technique in microbiology?
✔✔ To prevent contamination of cultures and the environment.
What is the proper way to sterilize an inoculating loop?
✔✔ By holding it in the flame of a Bunsen burner until it glows red.
What is the function of the decolorizer in Gram staining?
✔✔ To remove the primary stain from Gram-negative cells.
What is the typical magnification achieved with a compound light microscope?
✔✔ Up to 1000x.
Why is it important to label agar plates on the bottom rather than the lid?
3
, ✔✔ To ensure the label remains with the sample even if the lid is misplaced.
What is a pure culture?
✔✔ A culture containing only one type of microorganism.
What is the significance of the zone of inhibition in an antibiotic susceptibility test?
✔✔ It indicates the effectiveness of the antibiotic against the tested microorganism.
What is the purpose of streaking for isolation on an agar plate?
✔✔ To obtain isolated colonies of bacteria.
How can you differentiate between a bacterial colony and a fungal colony on an agar plate?
✔✔ Bacterial colonies are usually smooth and shiny, while fungal colonies are often fuzzy or
powdery.
What is the purpose of using a selective medium in microbiology?
✔✔ To allow the growth of specific microorganisms while inhibiting others.
4
Education Edition) Questions and
Answers 100% Pass
What is the purpose of staining bacterial cells?
✔✔ To increase contrast and make the cells visible under a microscope.
What is the primary dye used in Gram staining?
✔✔ Crystal violet.
Why is iodine used in Gram staining?
✔✔ It acts as a mordant to form a complex with the crystal violet, making it adhere better to the
bacterial cell walls.
What color do Gram-positive bacteria appear after staining?
✔✔ Purple.
What color do Gram-negative bacteria appear after staining?
✔✔ Pink or red.
1
,Why is heat fixation performed before staining a bacterial smear?
✔✔ To kill the bacteria and fix them to the slide.
What is the main difference between Gram-positive and Gram-negative bacterial cell walls?
✔✔ Gram-positive bacteria have a thick peptidoglycan layer, while Gram-negative bacteria have
a thin peptidoglycan layer and an outer membrane.
What is the purpose of using safranin in the Gram stain procedure?
✔✔ It is a counterstain that colors Gram-negative bacteria pink.
What is the shape of cocci bacteria?
✔✔ Spherical.
What is the shape of bacilli bacteria?
✔✔ Rod-shaped.
What is the function of the condenser on a microscope?
2
,✔✔ To focus light onto the specimen.
Why is oil immersion used with the 100x objective lens?
✔✔ To reduce light refraction and increase resolution.
What is the purpose of the aseptic technique in microbiology?
✔✔ To prevent contamination of cultures and the environment.
What is the proper way to sterilize an inoculating loop?
✔✔ By holding it in the flame of a Bunsen burner until it glows red.
What is the function of the decolorizer in Gram staining?
✔✔ To remove the primary stain from Gram-negative cells.
What is the typical magnification achieved with a compound light microscope?
✔✔ Up to 1000x.
Why is it important to label agar plates on the bottom rather than the lid?
3
, ✔✔ To ensure the label remains with the sample even if the lid is misplaced.
What is a pure culture?
✔✔ A culture containing only one type of microorganism.
What is the significance of the zone of inhibition in an antibiotic susceptibility test?
✔✔ It indicates the effectiveness of the antibiotic against the tested microorganism.
What is the purpose of streaking for isolation on an agar plate?
✔✔ To obtain isolated colonies of bacteria.
How can you differentiate between a bacterial colony and a fungal colony on an agar plate?
✔✔ Bacterial colonies are usually smooth and shiny, while fungal colonies are often fuzzy or
powdery.
What is the purpose of using a selective medium in microbiology?
✔✔ To allow the growth of specific microorganisms while inhibiting others.
4
