Using the Products of the Light-Dependent Reaction (OCR A Level Biology): Revision Note

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 P_i by ATP synthase in a process called photophosphorylation (ADP + P_i → 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