* Gram-staining relies on differences in cell wall structure. Bacteria have a thick peptidoglycan layer in their cell walls, which traps the crystal violet stain. This makes them appear purple under the microscope.
* Human cells lack this thick peptidoglycan layer. Instead, they have a cell membrane and a more complex structure called the plasma membrane. This structure allows the crystal violet stain to easily wash away during the decolorization step.
* Gram-negative bacteria also lack a thick peptidoglycan layer. However, they have an outer membrane that prevents the crystal violet stain from being washed away completely. This gives them a pinkish appearance under the microscope.
Therefore, human cells appear colorless after the Gram stain procedure.
Important Note: The Gram stain is primarily used to differentiate between bacterial species, not to identify human cells.
