Multiple Choice
Which two types of acids are characteristic components of the Gram-positive cell wall, in addition to peptidoglycan?
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7. Prokaryotic Cell Structures & Functions
Gram-Positive Cell Walls
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Upon completion of the Gram stain, Gram-positive cells will appear:
A
green
B
purple
C
pink
D
colorless
Verified step by step guidance1
Understand the principle behind the Gram stain: it differentiates bacteria based on the structure of their cell walls, specifically the thickness of the peptidoglycan layer.
Recall that Gram-positive bacteria have a thick peptidoglycan layer which retains the crystal violet-iodine complex during the staining process.
Recognize that after the decolorization step with alcohol or acetone, Gram-positive cells remain purple because the thick peptidoglycan traps the crystal violet dye.
Contrast this with Gram-negative bacteria, which have a thinner peptidoglycan layer and do not retain the crystal violet, instead taking up the counterstain (usually safranin) and appearing pink.
Therefore, conclude that upon completion of the Gram stain, Gram-positive cells will appear purple.
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