Multiple Choice
The Gram stain works because of differences in the ________ of bacteria.
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7. Prokaryotic Cell Structures & Functions
Gram-Positive vs. Gram-Negative Cell Walls
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After the Gram staining procedure, Gram-positive cells appear ______.
A
pink
B
green
C
colorless
D
purple
Verified step by step guidance1
Understand the purpose of Gram staining: it differentiates bacteria into Gram-positive and Gram-negative based on the structure of their cell walls.
Recall that Gram-positive bacteria have a thick peptidoglycan layer which retains the crystal violet-iodine complex during the staining process.
During the decolorization step, Gram-positive cells resist losing the crystal violet stain because of their thick peptidoglycan, while Gram-negative cells lose it.
After applying the counterstain (usually safranin), Gram-negative cells appear pink, but Gram-positive cells remain the color of the crystal violet stain.
Therefore, Gram-positive cells appear purple after the Gram staining procedure.
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