Question

how does gram staining separate bacteria into two groups?!?!!? please help!

Answer 1

The Gram stain broadly differentiates bacteria based on the composition of their cell wall. The Gram stain gets stuck in the peptidoglycan layer of the cell wall. Some bacteria have a thick peptidoglycan layer, so it can hold a lot of the stain and make the cells appear purple - these bacteria are Gram-positive. Bacteria with thinner cell walls cannot retain the Gram stain as well and so do not appear a deep purple - these bacteria are Gram-negative.

See here: https://en.wikipedia.org/wiki/Gram_staining