Final answer:
In the photosystem I reaction center, light energy is transferred to a special chlorophyll a called P700.
Step-by-step explanation:
In the photosystem I reaction center, light energy captured by pigment molecules is passed to a special reaction center chlorophyll a called P700. This is different from photosystem II, where the special chlorophyll a is known as P680. Within photosystem I, the electron necessary to replace the excited electron comes from the chloroplast electron transport chain.