Interdependence of Photosynthetic Reactions (DP IB Biology)

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