Because of the way the reactions are coupled, there exist multiple "fast" timescales (i.e., t c1 and t * s2 ) that characterize the time it takes for the trajectory to reach M ε,δ * . However, the accumulation of s 2 and c 2 will occur in QSS if λ * 1. While it is not possible to get a complete, four-dimensional picture of M ε,δ * , we can look at projections of the manifold on the s 1 -c 2 and s 1 -s 2 phase-planes to visualize the slow/fast dynamics (see Fig. ). Additionally, since both s 2 and c 2 are fast variables, M ε,δ * in the s 2 -c 2 phase-plane is equivalent to the moving intersection of the c 2 and s 2 -nullclines: