Fungi include, among others things, moulds, yeasts, and higher fungi. The cell membranes of all fungus are eukaryotic and contain sterols but not peptidoglycan. Their cell walls are made of cellulose, the same substance that plants use to construct their structures. Most fungi are aerobic chemoheterotrophs, meaning they require organic food. A large number of fungus are also saprophytes, which obtain their food by consuming decaying organic matter from the soil and water. In the histology lab, fungi stains continue to be an essential diagnostic tool for locating pathogenic bacteria.