DescriptionTwo examples each representing a biological network under oscillating conditions and in equilibrium are studied in the thesis. In the first problem, we recall a new methodology for the simulation and control of large metabolic systems called LIFE (Linear in Flux Expressions) introduced in a recent paper. The second problem focuses on the rhythmic behavior of an organism’s biological system. Circadian rhythms are observed in most organisms on earth and are known to play a major role in successful adaptation to the 24-h cycling environment. Circadian phenotypes are characterized by a free-running period that is observed in constant conditions and an entrained phase that is observed in light-dark conditions. The relationship between the free-running period and phase of entrainment is of interest. Our analyses support the view that the circadian period of an organism is not the only predictor of the entrained phase.