The light reactions take place in the thylakoid membrane of the chloroplast. Light activates the system using antenna complexes to collect the light and transfers that energy into the reaction center. Chemical reactions from the reaction center stores some of this chemical energy by transferring electrons to an electron acceptor molecule (NADP+, or nicotinamide adenine dinucleotide phosphate becomes the reduced form, NADPH). This causes the reaction center to become oxidized.
These reaction centers work in sync with each other, and are called Photosystems I and II in a Z-scheme.
Photosystem II (PSII) is a system that absorbs red light at 680nm. PSII is a strong oxidant, which can split water molecules into oxygen, protons and electrons with the cofactor manganese: 2 water --> oxygen + 4 protons + 4 electrons.
The electrons get fed into the system for ATP synthesis via the electron carriers, pheophytin and 2 plastoquinones, while the protons are left in the thylakoid lumen, providing a more acidic environment in comparison to the stroma.
Photosystem I (PSI) absorbs far-red light at wavelengths that are greater than 680nm. PSI is a strong reductant, which can reduce NADP+ to NADPH from the electron transfer that was generated from light. PSI transfers the electrons to ferredoxin, a electron carrier, which can then transfer the electrons over to ferredoxin-NADP reductase, a membrane associated flavoprotein, which reduces NADP+ to NADPH.
Cytochrome b6f complex is a multi-subunit protein complex, which helps shuffle electrons over from PSII to PSI, as well as increase the amount of protons in the thylakoid lumen. From the plastoquinone, electrons are transmitted to the cytochrome b6f complex. These electrons are then cycled through the complex either by the noncyclic/linear process, or through the Q-cycle. This causes oxidation of the 2 plastoquinones that had been previously reduced in the system, as well as transporting the electrons over to the electron carrier plastocyanin. Plastocyanin will then transfer the electrons to PSI.
ATP (adenosine triphosphate) synthesis is generated by the transmembrane protein, ATP Synthase. The energy required to generate ATP is created during the electron transfer chain: the protons that are sequestered in the thylakoid lumen. The protons are actively transported out of the thylakoid lumen by ATP Synthase, which causes a complementation change to its structure and synthesizes ADP (adenosine diphosphate) + inorganic phosphate to ATP.