Photosystem I operates with the functions of producing NADPH, the reduced form of NADP(Fd + NADH + 2 NADP + H = Fd + NAD + 2 NADPH.)[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2944534/#:~:text=It%20was%20found%20that%20the,%2B%20NAD%2B%20%2B%202%20NADPH.], at the end of the photosynthetic reaction through electron transfer, and of providing energy to a [https://chem.libretexts.org/Bookshelves/General_Chemistry/Book%3A_Structure_and_Reactivity_in_Organic_Biological_and_Inorganic_Chemistry_(Schaller)/V%3A__Reactivity_in_Organic_Biological_and_Inorganic_Chemistry_3/09%3A_Photosynthesis/9.06%3A_Adding_a_Proton_Pump-_Cytochrome_b6f_Complex proton pump] and eventually ATP, for instance in cyclic electron transport.