Light harvesting in green plants:

Sunlight is absorbed through chlorophyll molecules.  Chlorophyll is a porphyrin in that nitrogen atoms are coordinated to a magnesium ion example for it is a magnesium porphyrin.  This difference with a heme in that the nitrogen atoms are synchronized to an iron atom to built an iron porphyrin.  Green plants hold two kinds of chlorophyll molecules, chlorophyll a and chlorophyll b, which differ slightly in structure and in the wavelength of light they can absorb. While light is trapped through chlorophyll  molecules  straightly,  various  accessory  pigments  also  exist  which absorb  light and pass the excitation  energy  on to chlorophyll  molecules.  Therefore the carotenoids are important accessory pigments in green plants whilst phycobilins are accessory pigments in photosynthetic bacteria. This pigment absorbs light at wavelengths different from in which of chlorophyll and so act together to maximize the light harvested.

When a chlorophyll molecule is excited through a quantum of light (a photon), an electron is excited to a higher energy orbital. The excited chlorophyll can cross on its extra energy to a neighboring chlorophyll molecule by exciton transfer (also called resonance energy transfer)   and   so   return   to   the   unexcited   state. In the other words, the high-energy electron itself should be passed on with the chlorophyll taking up a low-energy electron from another source.

The capture   of solar energy occurs in the photosystems.   Every photosystem consists of antenna complex and photosynthetic reaction middle.  The antenna complex is composed of various hundred chlorophyll molecules and accessory pigments clustered together in the thylakoid membrane. While a chlorophyll  molecule  in the antenna  complex  absorbs  light and is excited and  the energy  is passed  through exciton  transfer that is from molecule  to molecule,  and is at last channeled  to two special  chlorophyll  molecules  in the photosynthetic  reaction center. A reaction center passes on the energy as a high-energy electron to a chain of electron carriers in the thylakoid membrane.