What happen's in photosystem 1?

Photosynthesis converts the light energy from the sun into
chemical energy that is useful for the plants. There are two photosystems acting in
series within the thylakoid membranes of the chloroplast that catalyze the light induced
charge separation: Photosystem I (PSI) and Photosystem
II(PSII). The numbers indicate the order in which the photosystems were discovered.
Under normal conditions, electrons flow from PS II through cytochrome bf to
PSI.

Photosystem I (PSI) optimally absorbs photons of 
wavelength of 700 nm. It is responsible for providing high energy electrons with which
to reduce NADP+ to produce NADPH to be used in the Calvin
cycle.

Once the chlorophyll P700 gets excited, it will
transfer the electron to a set of 4Fe-4S clusters.From these clusters the electron is

transferred to ferredoxin (Fd) a water soluble mobile electron carrier
located in the stroma which contains a 2Fe-2S cluster coordinated to 4 cysteine
residues.  The electron transfer produces a positive charge on the special pair which is
neutralized by the transfer of
an electron from a reduced plastocyanin. The
transfer of electrons is from reduced ferredoxin to NADP +(catalyzed by ferredoxin-NADP
+  reductase which is flavoprotein). This complex contains a tightly
bound
FAD which accepts the electrons one at a time from ferredoxin.  The FADH2 then transfers
a hydride to NADP + to form NADPH.