Before revision:  However, parameter uncertainty is a predominant issue in Systems Biology : the dynamical systems consist of a large number of states and parameters, while measurement data are often very noisy and data points and repetitions are usually few. Hence techniques allowing the analytic computation of parameter vectors where a given system exhibits bistability are desirable. Here we present a new sufficient condition for a large class of mass action networks. This condition takes the form of linear inequality systems. And it is constructive in the sense that solutions to one of the inequality systems determine state and parameter vectors where the underlying mass action systems -- under explicitly stated genericity conditions -- undergo a saddle-node bifurcation  .
After revision:  However, parameter uncertainty is a predominant issue in Systems Biology . And on the other hand switching already arises with the occurrence of a saddle type steady state (characterized by a Jacobian where exactly one Eigenvalue is positive and the remaining eigenvalues have negative real part). Consequently we derive conditions based on linear inequalities that allow the analytic computation of states and parameters where the Jacobian derived from a mass action network has a defective zero eigenvalue so that -- under explicitly stated genericity conditions -- undergo a saddle-node bifurcation .