The conversion of light energy into the free energy of organic compounds is the quintessence of photosynthesis. The primary process is the absorption of light by the antenna complexes and its transfer to the reaction center (RC) where photochemical energy storage take places. These are the most important proteins that catalyze the conversion of light energy into chemical energy and are known as type-I and type-II RCs. Type-I RCs use iron-sulfur clusters and are exemplified by photosystem I (PSI), found in plants, eukaryotic algae, and cyanobacteria. This complex catalyses the light-driven electron transfer from reduced plastocyanin to oxidized ferredoxin.