How do photosystems I and II help plants produce ATP and NADPH?

Photosystems I and II are essential components of the light reactions in photosynthesis, working together to convert light energy into chemical energy in the form of ATP and NADPH.12

NADPH Production

In photosystem I, light energy excites electrons in the pigment P${}_{700}$, which are then transferred through a series of carriers to ferredoxin. These electrons are ultimately used to reduce NADP${}^{+}$ to NADPH, a high-energy electron donor required for the subsequent conversion of carbon dioxide into carbohydrates.13

ATP Production

The production of ATP, or photophosphorylation, relies on a hydrogen ion (proton) gradient established across the thylakoid membrane. This gradient is created by:2
* The oxidation of water in photosystem II, which releases protons into the inner thylakoid space.2
* The transfer of electrons through the electron-transport chain, which pumps additional protons into the thylakoid.23

As protons flow back out of the thylakoid through an ATP-ase complex, the stored potential energy drives the synthesis of ATP from adenosine diphosphate (ADP) and inorganic phosphate.23