But notice that in order for this build up of H plus ions not to occur, these H plus ions must pass to this side. So this, in a way, acts as a sole bridge because if this membrane wasn't here, we'd have a build up of positive charge here and a lack of positive charge here. And then that means our electrons will stop flowing. So to close the circuit, we need this membrane. And so these H plus ions travel from the anode to the cathode. And when they reach this position, they react with the oxygen and the electrons forming water.