TECHNOLOGY FOCUS - POLYMERS - Preferred Fuel Cell: The fuel cell further comprises an anode redox polymer disposed on the anode for transducing a current between the anode and the anode enzyme, and a cathode redox polymer which is disposed on the cathode for transducing a current between the cathode and the cathode enzyme. The anode and cathode redox polymers have redox potential of at least +0.1 volts, respectively.    TECHNOLOGY FOCUS - BIOLOGY - Preferred Cathode: The cathode electroreduces oxygen in the presence of cathode enzyme which is laccase, cytochrome C peroxidase, or peroxidase. The cathode comprises a microporous membrane which has an outer layer having hydrophobic surface and an inner layer having an hydrophilic surface. The cathode enzyme is disposed on the inner layer of the microporous membrane.Preferred Anode: The anode electroxidizes at least one of sugar, alcohol or carboxylic acid in a biological system. The anode enzyme is oxidase or dehydrogenase. The anode enzyme is immobilized within an inorganic matrix which comprises redox functional groups and conductive particles distributed in the matrix. The anode enzyme is a thermostable enzyme.Preferred Fuel Cell: The fuel cell further comprises an additional enzymes proximally disposed to anode and is capable of breaking down at least one of starch or cellulose into sugar, alcohol or carboxylic acid.Preferred Process: The fuel cell is coupled to a storage device for storing electric power generated from the fuel cell. The fuel cell is inserted into biological systems such as animal, human, plant or plant residue. A biochemical in the system is electroxidized at anode and oxygen at cathode is electroreduced. The biological fluid which is venous or arterial blood is pumped through the fuel cell. EXAMPLE - An anode was formed by high surface area graphite fiber/carbon black electrode using polypropylene or polytetrafluoroethylene as binder. An anode redox polymer and an anode enzyme were disposed on the anode. A cathode was formed from oxygen or hydrogen peroxide permeable porous membrane. A cathode redox polymer and a cathode enzyme were disposed on the cathode. A fuel cell was obtained. An optional non-fouling coating was formed on the portions of electrodes of the fuel cell. The non-fouling coating containing hydrogel prevented penetration of macromolecules such as proteins into the electrodes. Anode redox polymer had redox potential of -0.65 to +0.05 V and cathode redox polymer had redox potential of +0.3 to +0.7 V. The enzymes of anode and cathode electrolysis layer catalyzed an electrochemical reaction of anode reductant and cathode oxidant, respectively. Different enzymes were provided in the anode and cathode electrolysis layer for e.g. laccase and cyctochrome C oxidase on the cathode for electroreduction of oxygen, peroxidase on the cathode for electroreduction of hydrogen peroxide, oxidase and dehydrogenase on the anode for electroxidation of glucose, lactate and other biochemicals, pyranose oxidase on the anode for electroxidation of D-glucose, L-sorbose and D-xylose, and glucose oxidase, oligosaccharide dehydrogenase or pyrroloquinoline quinone glucose dehydrogenase on the anode for electroxidation of glucose. The fuel cell was implanted in a blood vessel of an animal. The electric power generated by fuel cell was used to operate variety of devices such as pacemaker. The generated electric power was stored in storage devices such as capacitive storage element or battery.