Photosynthesis occurs in two stages: Light Reaction (Photochemical Phase) in the thylakoid membranes, producing ATP, NADPH, and O₂, and Dark Reaction (Calvin Cycle) in the stroma, where ATP and NADPH are used to fix CO₂ into glucose. All the stages are well-explained in the NCERT Class 11 Biology Chapter 11 Notes Photosynthesis in Higher Plants.