Question

multiple choice question
in this image, cells are illustrated as they would appear after each step of the gram stain procedure. which of the following statements is false?

• safranin is used as the counterstain to color cells that were decolorized.
• all cells appear purple after the first step because crystal violet is a simple stain.
• gram positive cells remain purple throughout the procedure.
• application of iodine results in the loss of color from gram negative cells.

Explanation:

1. Safranin is indeed the counterstain used to color Gram-negative cells that were decolorized, so this statement is true.
2. Crystal violet is a simple stain that dyes all bacterial cells purple in the first step of the Gram stain, so this statement is true.
3. Gram-positive cells have a thick peptidoglycan layer that retains the crystal violet-iodine complex through decolorization, staying purple throughout the procedure, so this statement is true.
4. Iodine acts as a mordant, forming a stable complex with crystal violet in all cells; color loss in Gram-negative cells occurs during the decolorization step (not iodine application), making this statement false.

Answer:

D. Application of iodine results in the loss of color from Gram negative cells.