  Aspects of cell metabolism are modeled by ordinary differential equations
describing the change of intracellular chemical concentrations. There is a
correspondence between this dynamical system and a complex network. As in the
classic Erd\H{o}s--R\'enyi model, the reaction network can evolve by the
iterative addition of edges to the underlying graph. In the biochemical
context, each added reaction implies a metabolic mutation. In this work it is
shown that modifications to the graph topology by gradually adding mutations
lead here too to the formation of a giant connected component, i.e., to a
percolation--like phase transition. It triggers an abrupt change in the
functionality of the corresponding network. This percolation is mapped into a
bifurcation in the intracellular dynamics. It acts as a shortcut in biological
evolution, so that the most probable metabolic state for the cell is suddenly
switched from cellular stagnation to exponential growth.
