Final answer:
Omitting the decolorizer from a Gram stain procedure will result in both Gram-positive and Gram-negative cells appearing purple, as the decolorization step that differentiates between the two types of cells is skipped. Option 4 is the correct answer.
Step-by-step explanation:
If a microbiologist omitted the decolorizer from a Gram-stained smear, all cells in the smear would be purple. The decolorizing step is crucial in the Gram staining procedure because it serves to differentiate between Gram-positive and Gram-negative bacteria based on the properties of their cell walls. Specifically, the decolorizer, which is typically alcohol, selectively removes the primary stain (crystal violet) from only the Gram-negative cells due to the structural differences in their cell walls.
Gram-positive bacteria have a thick peptidoglycan layer that retains the crystal violet stain, while the Gram-negative bacteria have a thinner peptidoglycan layer and an additional outer membrane that allow the crystal violet stain to be washed away during the decolorization step. Without the decolorizer, the differentiation step is bypassed, resulting in both Gram-positive and Gram-negative cells retaining the purple color of the crystal violet dye. Hence, the expected outcome when omitting the decolorizer is that both types of cells will remain stained with crystal violet, making them appear purple.