BIOL271 / BIOL 271 Module 3:
(Latest Update )
Microbiology | Questions & Answers
| Grade A | 100% Correct - Portage
Learning
Question:
What dyes are used in Gram staining, and how do they work on Gram-positive
cells?
Answer:
Crystal violet and iodine form a stable complex trapped in the thick
peptidoglycan wall.
Question:
What color do Gram-positive bacteria appear after staining?
Answer:
Purple
,Question:
What is the main structural difference in Gram-negative bacteria?
Answer:
They have a thin peptidoglycan layer and an outer membrane made of
lipopolysaccharides (LPS).
Question:
What happens to Gram-negative bacteria during the alcohol decolorization
step?
Answer:
The alcohol removes the crystal violet dye and depletes the color from the
outer membrane.
Question:
Why are Gram-positive bacteria unaffected by the decolorization step?
Answer:
Their thick peptidoglycan wall retains the crystal violet-iodine complex.
,Question:
What dye is used as a counterstain in the Gram stain process?
Answer:
Safranin
Question:
What color do Gram-negative bacteria appear after counterstaining?
Answer:
Pink
Question:
What does the Gram stain differentiate between?
Answer:
Bacteria with thick vs. thin (or absent) peptidoglycan layers.
Question:
What is a differential stain?
Answer:
A stain that uses two or more dyes to separate organisms into subgroups
based on structural differences.
, Question:
Why must cells be fixed to a slide during staining?
Answer:
To prevent the sample from washing off during staining and rinse steps.
Question:
What is the most common fixation method used in Gram staining?
Answer:
Heat fixation
Question:
How is heat fixation performed?
Answer:
The sample is placed on a slide and passed through a flame until all liquid
evaporates.
Question:
What is a disadvantage of fixation (heat or chemical)?
Answer:
It kills the microorganism, so motility cannot be observed.
(Latest Update )
Microbiology | Questions & Answers
| Grade A | 100% Correct - Portage
Learning
Question:
What dyes are used in Gram staining, and how do they work on Gram-positive
cells?
Answer:
Crystal violet and iodine form a stable complex trapped in the thick
peptidoglycan wall.
Question:
What color do Gram-positive bacteria appear after staining?
Answer:
Purple
,Question:
What is the main structural difference in Gram-negative bacteria?
Answer:
They have a thin peptidoglycan layer and an outer membrane made of
lipopolysaccharides (LPS).
Question:
What happens to Gram-negative bacteria during the alcohol decolorization
step?
Answer:
The alcohol removes the crystal violet dye and depletes the color from the
outer membrane.
Question:
Why are Gram-positive bacteria unaffected by the decolorization step?
Answer:
Their thick peptidoglycan wall retains the crystal violet-iodine complex.
,Question:
What dye is used as a counterstain in the Gram stain process?
Answer:
Safranin
Question:
What color do Gram-negative bacteria appear after counterstaining?
Answer:
Pink
Question:
What does the Gram stain differentiate between?
Answer:
Bacteria with thick vs. thin (or absent) peptidoglycan layers.
Question:
What is a differential stain?
Answer:
A stain that uses two or more dyes to separate organisms into subgroups
based on structural differences.
, Question:
Why must cells be fixed to a slide during staining?
Answer:
To prevent the sample from washing off during staining and rinse steps.
Question:
What is the most common fixation method used in Gram staining?
Answer:
Heat fixation
Question:
How is heat fixation performed?
Answer:
The sample is placed on a slide and passed through a flame until all liquid
evaporates.
Question:
What is a disadvantage of fixation (heat or chemical)?
Answer:
It kills the microorganism, so motility cannot be observed.
