During this electrochemical reaction, the electrons passthrough
the outer circuit to generate electricity .It is interesting
to note that the catalytic four-electron reduction of oxygen to
water could take place at an enzyme electrode in a neutral
solution. Due to the selective reactivity of the enzymes at each
electrode, no cross reaction occurs between the anode and
cathode. In general the Bio batteries could be classified into
many types based on fuel containment, fuel and catalyst
sources, origin of the catalytic enzymes and the method of
electron transfer between reaction site and electrode