Occurs in two stages:

1) Light dependent reactions (LDR)

- photon hits chlorophyll molecule in PS II and excites electron. Photolysis of H₂O into oxygen, protons and electrons is triggered

- released electrons pass through series of electron carriers before reaching PS I

- at PS I, electrons are excited again by incident photons. They pass through ferredoxin electron carrier

- Electrons can either travel back to plastoquinone, powering proton pump or reach NADP reductase enzyme where NADP+ ions are reduced to NADPH

- Proton gradient powers production of ATP from ATP-ase enzymes in thylakoid membrane

2) Light independent reactions

- rubisco enzymes catalyses the fixing of the CO₂ molecule to the 5-carbon ribulose biphosphate

- decays into two 3- carbon molecules of phosphoglycerate

- ATP from LDR is used to form diphosphoglycerate

- NADPH used to reduce this to GALP

- one molecule of GALP is removed per 3 molecules of CO₂ and the rest are modified into (i) ribulose phosphate and (ii) ribulose biphosphate