Ans. B: Gram positive bacteria The Bacteria (eubacteria), with the exception of the Chlamydias have a semirigid cell wall containing peptidoglycan. Gram negative bacteria's peptidoglycan layer is much thinner than in Gram-positive bacteria In general, the walls of gram positive bacteria have a simpler chemical nature than those of gram negative bacteria. The mycoplasmas are the only bacteria that naturally lack a cell wall. Mycoplasmas maintain a nearly even pressure between the outside environment and the cytoplasm by actively pumping out sodium ions. Their cytoplasmic membranes also contain sterols that most likely provide added strength. All other bacteria have a cell wall Peptidoglycan prevents osmotic lysis. Under the cytoplasmic membrane, bacteria concentrate dissolved nutrients (solute) through active transpo. As a result, the bacterium's cytoplasm is usually hypeonic to its surrounding environment and the net flow of free water is into the bacterium. Without a strong cell wall, the bacterium would burst from the osmotic pressure of the water flowing into the cell.