Often the time of influence of the open system on the environment or the environment on the system may be of such lengthy duration or of such minimal nature as to limit its need to be considered. In 1927 Ludwig von Bertalanffy first proposed that the human organism should be treated as an open system. Any system taken in a large enough context can be considered a closed system. It is often more appropriate to consider a system as a subsystem of some larger system which must interact in some way with the larger system. Taking the larger system into account is unnecessary for understanding the operation of the subsystem.
All systems are both subsystems of larger systems and composed of subsystems at the same time.
These provide a means of understanding some general characteristics of systems. These systems are arranged in what is considered an evolutionary hierarchy. This is a system in which a positive influence from one element to another provides a negative influence in return to the first element. I get positive things from you and provide you a negative return in response. Essentially I subsist on you.