The metabolic versatility of bacteria is a source of learning difficulty for students in classical microbiology courses. To facilitate the learning process, the authors developed an advance organizer. It consists of a set of six diagrams of metabolic pathways describing the basic living requirements of several types of bacteria: energy, carbon sources, and oxidizable substrates that provide electrons for reductive biosyntheses. The students are presented with the six diagrams and at the same time with one problem that must be resolved using solely the set of diagrams, with no access to any textbook. This procedure aims at developing the skills necessary to analyze different (and perhaps more complex) metabolic processes than those represented by the diagrams.