A photosystem is an aggregate of protein structures in the thylakoid membranes of plants that aids in photosynthesis. It absorbs light energy and transfers electrons onto a reaction center. Thylakoid membranes are found in the plant chloroplasts.
The photosystem consists of carotenoids, chlorophyll I and chlorophyll II molecules that together form an antennae complex. This complex harvests light energy from a broad range of the light spectrum and, through a series of resonance, transfer electrons down the various pigments up to the reaction center. The reaction center then utilizes the energy to activate a series of enzymes, which then perform the actual splitting of water molecules in photosynthesis.