Bacterial Cell Envelopes and What the Gram Stain Reveals · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Why the stain splits bacteria in two

Science · Microbiology · ages 18-19
Name ______________________   Date ____________

  1. Which wall belongs to a Gram positive cell?

    • Thin wall plus outer membrane
    • No wall at all
    • Thick peptidoglycan coat

  2. What is the order of the four stain steps?

    • Iodine, safranin, crystal violet, decolorizer
    • Crystal violet, iodine, decolorizer, safranin
    • Decolorizer, crystal violet, safranin, iodine

  3. The decolorizer step is the critical moment where the two groups diverge.

    Circle one:   True   False

  4. Why do Gram negative cells resist some antibiotics?

    • They grow too fast for drugs
    • They digest every drug
    • Their outer membrane blocks drug entry

  5. The decolorizer runs too long. What happens?

    • Negatives stay purple
    • Positives turn pink
    • All cells turn purple

  6. A growing cell cannot cross link its wall. What happens?

    • It stops staining entirely
    • Water rushes in and it bursts
    • It builds a second membrane

  7. How does the stain result help choose treatment?

    • Pink cells warn of an outer membrane barrier
    • Purple cells always need stronger drugs
    • Colour alone picks the exact drug

  8. A new drug is large and water fearing. Which cells will it struggle to enter?

    • Gram positive cells
    • Both groups equally
    • Gram negative cells
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Why the stain splits bacteria in two W1-mt_Q5zM0oO3Vu-s1

  1. Thick peptidoglycan coat · Gram positive cells wear a thick peptidoglycan coat.
  2. Crystal violet, iodine, decolorizer, safranin · Crystal violet first, iodine to lock it, decolorizer, then safranin.
  3. True · That wash keeps purple in thick walls and rinses it from thin ones.
  4. Their outer membrane blocks drug entry · The outer membrane is a barrier to many large drugs.
  5. Positives turn pink · Over washing strips dye even from thick walls.
  6. Water rushes in and it bursts · Without cross links the wall weakens and water bursts the cell.
  7. Pink cells warn of an outer membrane barrier · A pink result predicts the barrier that blocks some antibiotics.
  8. Gram negative cells · The outer membrane barrier predicts poor entry into Gram negative cells.
Worksheet · LightMySky