P 680 replaces its electrons by extracting them from a water molecule. As electrons move along the chain ATP is formed. P 700 becomes oxidized. Electrons go from the reaction center to the electron acceptor downhill back to the reaction center. ATP is generated in this process.
Carbon is available as carbon dioxide.
A reaction pathway known as the Calvin or Calvin-Benson Cycle and is like the Krebs Cycle because by the end of each turn of the cycle, the starting compound has been regenerated. It is a food and forms in the grana. PGAL is also usable directly as a building material and can form chlorophyll, NADP, or Ribulose 5-P or any of the enzymes taking part in carbon dioxide fixation. More PGAL is usually manufactured than needed - the bulk is available for export to nonphotosynthesizing cells of the plant. PGAL is too reactive to be exported as such but is transformed into sugars such as sucrose, glucose, or fructose.