SME
Microbiology
Microbial structure
Use this for “Which cells have an outer membrane with LPS, and which stain purple?”
Sort
Gram-positive, Gram-negative or both?
Tap a card, then tap its group.
Compare each feature with the two walls drawn on the bins.
Assumptions
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Crystal violet stains every cell; iodine locks it into the peptidoglycan; alcohol then washes it out of a thin wall.
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Safranin, the counterstain, turns the washed-out cells pink.
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Every bacterium has a plasma membrane and 70S ribosomes, whatever its wall.
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Shape alone does not tell the stain: cocci and bacilli can be either.
Topic check
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