AQA A Level Biology复习笔记5.1.4 Using the Products of the Light Dependent Reaction

The Two Stages of Photosynthesis


  • 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


Exam Tip

Remember, the whole purpose of the light-dependent reactions is to produce ATP and reduced NADP, which are then used to complete the process of photosynthesis through the light-independent reactions.