Using the Products of the Light-Dependent Reaction
- Photosynthesis occurs in two stages: the light-dependent stage, which takes place in the thylakoids, and the light-independent stage, which takes place in the stroma
- During the light-dependent stage of photosynthesis:
- Reduced NADP is produced when hydrogen ions combine with the carrier molecule NADP using electrons from the photolysis of water
- ATP is produced from ADP and Pi by ATP synthase in a process called photophosphorylation (ADP + Pi → ATP)
- Photophosphorylation uses the proton (H+) gradient generated by the photolysis of water
- Energy from ATP and hydrogen from reduced NADP are passed from the light-dependent stage to the light-independent stage of photosynthesis
- The energy and hydrogen are used during the light-independent reactions (known collectively as the Calvin cycle) to produce complex organic molecules, including (but not limited to) carbohydrates, such as:
- Starch (for storage)
- Sucrose (for translocation around the plant)
- Cellulose (for making cell walls)
Photosynthesis occurs in two, closely-linked stages: the light-dependent stage, which takes place in the thylakoids, and the light-independent stage, which takes place in the stroma
Examiner Tip
Remember, the whole purpose of the light-dependent stage is to produce ATP and reduced NADP, which are then used to complete the process of photosynthesis through the light-independent stage.
