Photosynthesis is considered the most important process in the biosphere. A chain of four complex protein molecules localized in the chloroplasts (Photosystem II (PSII), Photosystem I (PSI), Cytochrome b6f (Cyt.b6f), and ATP synthase), plus several removable proteins, known as Plastoquinone (PQ), Plastocyanin (PC), Cytochrome c6 (Cyt.c6), and Ferredoxin (Fd), recreate or convert the solar energy into a double electron stream, both cyclic and linear. This book proposes the hypothesis that the physiological motif of plastocyanin dimorphism is a hallmark of higher plants. The book will also serve as a methodological guide to photosynthesis, as it offers various methods for the study of proteins.