Using the Products of the Light Dependent Reaction (AQA A Level Biology)

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The Two Stages of Photosynthesis

  • Photosynthesis occurs in two stages:
    • The light-dependent stage, which takes place in the thylakoids
    • The light-independent stage, which takes place in the stroma

Summary of the light-dependent stage 

  • Reduced NADP is produced when hydrogen ions combine with the carrier molecule NADP using electrons from the photolysis of water
  • ATP is produced  in a process called photophosphorylation 
    • 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

Summary of the light independent stage

  • The energy and hydrogen (from the light dependent stage) are used
  • This takes place in reactions known collectively as the Calvin cycle
  • Complex organic molecules are produced, including (but not limited to) carbohydrates, such as:
    • Starch (for storage)
    • Sucrose (for translocation around the plant)
    • Cellulose (for making cell walls)

The two stages of photosynthesis, downloadable AS & A Level Biology revision notes

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

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Lára

Author: Lára

Expertise: Biology Lead

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.