Rate curves  of system (2) for the parameters k1 = 8, k2 = 1, k3 = 1, k4 = 1.5. The thick solid line is the rate of the removal of reactant X (sum of the negative terms in ) and the thick dashed line the rate of production (positive term in ). The three crossings indicate the three steady states . The thin lines show the contributions of the three degradation terms separately: quadratic term k2x2 dashed, the effectively cubic term k3 xy solid, and the linear term k4 x dotdashed. The inset shows a zoomed version for x < 2.1.
Wilhelm BMC Systems Biology 2009 3:90 doi:10.1186/1752-0509-3-90