Multiple Choice
The outcome of the Gram stain is based on differences in the cell's _______.
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7. Prokaryotic Cell Structures & Functions
Gram-Positive vs. Gram-Negative Cell Walls
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During the Gram stain procedure, which type of cells decolorize when the alcohol is applied?
A
Gram-positive cells
B
Neither Gram-positive nor Gram-negative cells
C
Gram-negative cells
D
Both Gram-positive and Gram-negative cells
Verified step by step guidance1
Understand the purpose of the Gram stain procedure: it differentiates bacterial cells into Gram-positive and Gram-negative based on their cell wall structure.
Recall that during the Gram stain, crystal violet dye initially stains all cells purple, and then iodine is applied to form a crystal violet-iodine complex inside the cells.
When alcohol (decolorizer) is applied, it interacts differently with the cell walls: Gram-positive cells have a thick peptidoglycan layer that retains the crystal violet-iodine complex, so they remain purple.
Gram-negative cells have a thinner peptidoglycan layer and an outer membrane; the alcohol disrupts the outer membrane and washes out the crystal violet-iodine complex, causing these cells to lose the purple color (decolorize).
Therefore, the cells that decolorize upon alcohol application are the Gram-negative cells.
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