This paper deals with a generic approach for the analysis of interconnected biological systems. The equilibrium points as well as the asymptotic behaviour of these systems are investigated from a qualitative point of view. In particular, a new generic approach is used to show that a series of Continuously Stirred Tank Reactors (CSTRs) can exhibit multiple steady state profiles, for any non-monotonic kinetics. This multiplicity property disappears when the number of reactors becomes sufficiently large (for a given total volume). These results are to be taken in account when CSTRs in series are used to approximate a Piston Flow Reactor (PFR).