What are the two components to a photosystem?

A photosystem comprises:_
1. several (>10 or >11) protein subunits, providing a scaffold for a series of cofactors.
2.The latter can be pigments (like chlorophyll, pheophytin, carotenoids), quinones or iron-sulfur clusters. Because chlorophyll a can only absorb light of a narrow wavelength, it works with the antenna pigments to gain energy from a larger part of the spectrum.
3.The pigments absorb light of various wavelengths and pass along their gained energy to the reaction center chlorophyll. When the energy reaches the chlorophyll a, it releases two electrons into an electron transport chain.

Photosystem II (PSII) works with photosystem I (PSI)  and two series of enzymatic reactions.
PSII is made up of  chlorophyll that absorb the solar energy with a peak at 680 so the reaction center is called the P680. It captures photons and uses the energy to extract electrons from water molecules.
PSI receives the electrons via a transport chain across the thykaloid membrane from PSII.

PSI is thought to be the older system and it resembles that used by the green sulfur bacteria & heliobacteria.
At PSI core are two chlorophylls known as P700 for its peak absorption wavelength. This is surrounded by the antenna array and all is held together by protein structures.
http://www.hpc.unm.edu/~aroberts/main/psi.htm

Evolution of the tandem use of two photocenters is possibly a case of symbiotic merging or some other mechanism of lateral genetic transference between species. Photosynthetic purple bacteria and green non-sulfur bacteria have a PSII-like system still. Green sulfer bacteria are PSI users. Cyanobacteria use the two systems in tandem. So it seems the two systems evolved separately from a common ancestor because they have important similarities then they were rejoined in a synergistic system.
http://books.google.com/books?id=bRWd5bGhXM4C&pg=PA262&lpg=PA262&dq=photosystem+evolution&source=web&ots=fgswELJoKW&sig=E4eGOZ_iSiG5aNkFdfkg1wZm5GI&hl=en&sa=X&oi=book_result&resnum=5&ct=result#PPA260,M1

antenna complex

which directs photon to reaction center

and reaction center
which uses the photon