mediator and a micro-organism such as yeast, are mixed together in a solution to which is added a substrate such as glucose. This mixture is placed in a sealed chamber to prevent oxygen from entering, thus forcing the micro-organism to undertake anaerobic respiration. An electrode is placed in the solution to act as the anode. In the second chamber of the MFC is another solution and the positively charged cathode. It is the equivalent of the oxygen sink at the end of the electron transport chain, external to the biological cell. The solution is an oxidizing agent that picks up the electrons at the cathode. As with the electron chain in the yeast cell, this could be a variety of molecules such as oxygen, although a more convenient option is a solid oxidizing agent, which requires less volume. Connecting the two electrodes is a wire (or other electrically conductive path). Completing the circuit and connecting the two chambers is a salt bridge or ion-exchange membrane. This last feature allows the protons produced, as described in , to pass from the anode chamber to the cathode chamber. The reduced mediator carries electrons from the cell to the electrode. Here the mediator is oxidized as it deposits the electrons. These then flow across the wire to the second electrode, which acts as an electron sink. From here they pass to an oxidizing material. Also the hydrogen ions/protons are moved from the anode to the cathode via a proton exchange membrane such as Nafion. They will move across to the lower concentration gradient and be combined with the oxygen but to do this they need an electron. This generates current and the hydrogen is used sustaining the concentration gradient. Algal biomass has been observed to give high energy when used as the substrate in microbial fuel cell. See also Biobattery Cable bacteria Dark fermentation Electrohydrogenesis Electromethanogenesis Fermentative hydrogen production Glossary of fuel cell terms Hydrogen hypothesis Hydrogen technologies Photofermentation Bacterial nanowires References Yue P.L. and Lowther K. (1986). Enzymatic Oxidation of C1 compounds in a Biochemical Fuel Cell. The Chemical Engineering Journal, 33B, p 69-77 Further reading External links DIY MFC Kit BioFuel from Microalgae Sustainable and efficient biohydrogen production via electrohydrogenesis – November 2007 Microbial Fuel Cell blog A research-type blog on common techniques used in MFC research. Microbial Fuel Cells This website is originating from a few of the research groups