Chapter 25 - Bacteria, Archaea, and Viruses - 25.1 - Bacteria and Archaea Are the Two Primary Divisions of Life - 25.1 Recap - Learning Outcomes - Page 533: 2

Gram staining was used as a method of classifying bacteria. After a dye was applied, the cell walls of bacteria react depending on their composition. Gram-positive bacteria have a thick peptidoglycan cell wall that appears blue or purple. Gram-negative bacteria have a thin peptidoglycan layer that appears pink or red by picking up the counterstain.

Gram staining was used as a method of classifying bacteria. After a dye was applied, the cell walls of bacteria react depending on their composition. Gram-positive bacteria have a thick peptidoglycan cell wall that appears blue or purple. Gram-negative bacteria have a thin peptidoglycan layer that appears pink or red by picking up the counterstain.