  Photosynthesis is the primary energy production process of ecosystem.
Throughout the green plants, two different types of chlorophylls, Chl-a and -b,
are bound to the light-harvesting complex for photosystem II. While the
structure and functional characteristics of the two types of chlorophylls have
been well documented as individual, the features of the coexistence has yet to
be understood clearly. Here, we present a principled framework for discerning
and quantifying the chlorophylls' role during the excited energy transfer. Our
approach combines network science and Monte Carlo Markov analysis based on the
Foerster resonance energy transfer rates between all the chlorophyll pairs in
the light-harvesting antennae for photosystem II. We find that the excitation
energy can be rapidly confined to the specific chlorophyll clusters in the
light-harvesting complex, where excess energy dissipation possibly takes place,
only when both chlorophyll species are involved. Comparing to other models with
hypothetical chlorophyll compositions, we show that the light harvesting system
with natural chlorophyll a and b ratio is the most advantageous for the
photosystem II supercomplex to balance the light-harvesting and photoprotection
capabilities.
