Several deterministic models will be presented to illustrate the special types of mechanisms that regulate and control cell metabolism. Stochastic analysis can be used to investigate such highly nonlinear deterministic dynamical systems that typically operate far from equilibrium. Examples will be given that show how specific biological system properties depend on the natural stochasticity inherent in diffusion processes and in the making and breaking of chemical bonds. On many different space and time scales, evolution has selected stochastic mechanisms for accomplishing specific biological functions. Finding, characterizing, and explaining these mechanisms requires cooperative research by biologists and stochastic analysts. The tasks are daunting because biology is really hard.