  Reaction systems are discrete dynamical systems that model biochemical
processes in living cells using finite sets of reactants, inhibitors, and
products. We investigate the computational complexity of a comprehensive set of
problems related to the existence of fixed points and attractors in two
constrained classes of reaction systems, in which either reactants or
inhibitors are disallowed. These problems have biological relevance and have
been extensively studied in the unconstrained case; however, they remain
unexplored in the context of reactantless or inhibitorless systems.
Interestingly, we demonstrate that although the absence of reactants or
inhibitors simplifies the system's dynamics, it does not always lead to a
reduction in the complexity of the considered problems.
