Metabolism, the sum of all chemical reactions within a living organism, is one of the most fundamental concepts presented in introductory microbiology courses. However, it is often difficult for instructors to effectively translate perfunctory diagrams of glycolysis, the Krebs cycle, and the electron transport chain in a way that is meaningful to students. An understanding of metabolism is integral to the appreciation of microbial life, and it behooves microbiology instructors to place the study of metabolism in a context that facilitates this appreciation. The electrochemical nature of many biological processes may provide an avenue for such an endeavor. Biological fuel cells link respiratory reactions within a microbial cell with reactions that occur in electrochemical cells. The generation of an anodic electrode potential, or flow of electrons, within the biological fuel cell is catalyzed by the oxidative degradation of substrates by microorganisms. This article presents an exercise that describes the construction and testing of a simple biological fuel cell. While this biological fuel cell is not highly efficient or state-of-the-art in its design, it can be constructed and run with materials common to most biological laboratories. The exercise requires students to think in a multidisciplinary way, drawing on their knowledge of biology, chemistry, biochemistry, and physics. This system can serve the dual purpose of demonstrating the potential benefits of microbial life as well as providing context for the study of metabolic pathways. (Contains 3 figures.)