Please explain this diagram.

Dear student, There are two phases of photosynthesis- light reactions and dark reactions. Light reaction:- As the name suggests, this reaction takes place in the presence of light. Light energy is absorbed by chlorophyll molecules and is utilized for splitting water molecules into hydrogen and oxygen. Additionally in this phase, assimilatory power in the form of ATP and NADPH2 are produced. Light reactions occur in the membranes of thylakoids. Dark reactions – This reaction does not require direct light and occurs in the stroma of chloroplasts. During this phase, ATP and NADPH2 (formed during light reactions) are utilized for the reduction of CO2 to carbohydrates (food). Regards