Cycles such as a Rankine cycle, Calvin cycle, etc. play important roles. They consist of a set of specific processes and exhibit specific functions by this whole set of processes.
Two methods to examine those specific functions graphically are presented based on thermodynamics. The first method is to trace the ratio of the exergy gained to the energy gained by the circulating substance. The second method is to display release and acceptance of heat-equivalent as well as work-equivalent energies. Those methods reveals that loops have three important features; work (or work-equivalent energy) integration, creation of specific fields, and functions to purify a target component and to reduce wastes. All of these features are keys to create a sustainable society.