The organism as bioreactor. Interpretation of the reduction law of metabolism in terms of heterogeneous catalysis and fractal structure.

Organisms and bioreactors are open, dissipative systems in steady state. They are functionally equivalent with respect to turnover and kinetics, and structurally analogous with respect to fractal organization and self-similar scaling. As heterogeneous catalytic systems both are governed by interaction of mass transport and reaction. The structural equivalent to turbulence in the reactor, yielding high efficiency, is the fractal folding and branching of the transport systems of the organism. Dimensionally and in terms of fractals, organisms and reactors are therefore area-volume hybrids. The physiological consequence of this is the reduction law of metabolism. Introducing limits into allometric functions describing scale-up of similar organisms yields probability density distributions of their realization.