Gram-positive bacterial cell wall, artwork. The horizontal layers include a plasma membrane (blue) containing transmembrane proteins (green, yellow and purple). Above this is a thick peptidoglycan layer (purple rods) that is held together by teichoic acids (red rods) and lipoteichoic acids (green rods). This is termed a Gram-positive cell wall because the thick layer of peptidoglycan retains the Gram stain that helps identify microbial life.