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First exams 2025

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Interdependence of Photosynthetic Reactions (HL) (HL IB Biology)

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Interdependence of Photosynthetic Reactions

  • The light dependent reaction and light independent reaction are interdependent
  • This means that one cannot occur without the other
    • Products from the light dependent reaction (reduced NADP and ATP) are directly used in the Calvin cycle to produce carbohydrates
      • This means that in low light intensity, the products are produced at a slower rate which limits the conversion of GP to TP
    • Once the reduced NADP has been oxidised in the Calvin cycle, NADP is returned to the light dependent stage to accept electrons at the end of the electron transport chain
      • In high light intensity, the light dependent reactions occur more quickly, providing more reduced NADP and ATP to drive the Calvin cycle
      • However, if NADP is not returned to the light dependent stage quickly enough, then the process will be restricted
  • Carbon dioxide, in the form of hydrogen carbonate ions (HCO3-), accepts protons from photosystem II when water is split during photolysis
    • Hydrogen carbonate also plays an important role in the functioning of the electron transport chain
  • A lack of carbon dioxide (and thus hydrogen carbonate) will not only prevent carbon fixation from occurring but also prevent photosystem II from functioning

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Ruth

Author: Ruth

Expertise: Biology

Ruth graduated from Sheffield University with a degree in Biology and went on to teach Science in London whilst also completing an MA in innovation in Education. She gained 10 years of teaching experience across the 3 key science disciplines and physical education. Ruth decided to set up a tutoring business to support students in her local area. Ruth has worked with several exam boards and loves to use her experience to produce educational materials which make the mark schemes accessible to all students.