The adaptation of plants to a perpetually changing environment is approached as an optimisation strategy dictated by the thermodynamic demand for minimal entropy production, in a general effort of interpreting the behaviour of living systems in the frame of the Thermodynamics of Irreversible Processes in Open Systems. Therefore, it is necessary to create a bridge between the theoretical concepts and the phenomenological behaviour of the living system, which in this case is the photosynthetic apparatus. This bridging is succeeded through the J-K-B Trilogy, where the fluorescence kinetics, analysed according to the Theory of Energy Fluxes in Biomembranes, lead to the determination of a constellation of structural and functional parameters that quantify the system behaviour.