Theoretical example. a. Theoretical model presented by . All reactions were modelled as having reversible mass-action kinetics with rate constants equal to one. b. The seven elementary modes of the system, taking X0, X1 and X2 as external metabolites. Since all reactions in the system are reversible, all elementary modes are reversible as well. The direction of blue arrows therefore only refers to a conventional positive direction for elementary mode fluxes; a negative elementary mode flux means that the mode is running in the opposite direction. c. Variations of elementary mode fluxes for concentrations of X0 ranging from 0 to 5, while X1 and X2 have constant concentrations of 4 and 3 respectively.