  In green plants, chlorophyll-a and chlorophyll-b are the predominant pigments
bound to light-harvesting proteins. While the individual characteristics of
these chlorophylls are well understood, the advantages of their coexistence
remain unclear. In this study, we establish a method to simulate excitation
energy transfer within the entire photosystem II supercomplex by employing
network analysis integrated with quantum dynamic calculations. We then
investigate the effects of the coexistence of chlorophyll-a and chlorophyll-b
by comparing various chlorophyll compositions. Our results reveal that the
natural chlorophyll composition allows the excited energy to preferentially
flow through specific domains that act as safety valves, preventing downstream
overflow. Our findings suggest that the light-harvesting proteins in a
photosystem II supercomplex achieve evolutionary advantages with the natural
chlorophyll-a/b ratio, capturing light energy efficiently and safely across
various light intensities. Using our framework, one can better understand how
green plants harvest light energy and adapt to changing environmental
conditions.
