Conventional physics deals only with closed systems, i.e. systems which are considered to be isolated from their environment... However, we find syst… - Ludwig von Bertalanffy

We find systems which by their very nature and definition are not closed systems. Every living organism is essentially an open system. It maintains itself in a continuous inflow and outflow, a building up and breaking down of components, never being, so long as it is alive, in a state of chemical and thermodynamic equilibrium but maintained in a so-called steady state which is distinct from the latter.

Our conception is that of a theory about the system in an inertial state... if the organism is a system in an inertial state, as our law expresses it, the metabolic processes generally have to follow the established system; the ever progressing findings must replace the general expression of 'a system in an inertial state' by a more and more detailed knowing about the nature of this system and its chemical, osmotic, fermentive system conditions.

Mechanism... provides us with no grasp of the specific characteristics of organisms, of the organization of organic processes among one another, of organic 'wholeness', of the problem of the origin of organic 'teleology', or of the historical character of organisms... We must therefore try to establish a new standpoint which — as opposed to mechanism — takes account of organic wholeness, but... treats it in a manner which admits of scientific investigation.

If the variables are continuous, this definition [Ashby’s fundamental concept of machine] corresponds to the description of a dynamic system by a set of ordinary differential equations with time as the independent variable. However, such representation by differential equations is too restricted for a theory to include biological systems and calculating machines where discontinuities are ubiquitous.