CIE A Level Biology (9700) 2019-2021

Revision Notes

13.1.6 Photophosphorylation

Types of Photophosphorylation

  • The thylakoid membrane is the site of the light-dependent stage of photosynthesis
  • During the light-dependent stage of photosynthesis:
    • Light energy is used to breakdown water (photolysis) to produce hydrogen ions, electrons and oxygen in the thylakoid lumen
    • A proton gradient is formed due to the photolysis of water resulting in a high concentration of hydrogen ions in the thylakoid lumen
    • Electrons travel through an electron transport chain of proteins within the membrane
    • Reduced NADP (NADPH) is produced when hydrogen ions in the stroma and electrons from the electron transport chain combine with the carrier molecule NADP
    • ATP is produced during a process known as photophosphorylation (ADP + Pi → ATP) using the proton gradient between the thylakoid lumen and stroma to drive the enzyme ATP synthase
  • The photophosphorylation of ADP to ATP can be cyclic or non-cyclic, depending on the pattern of electron flow in photosystem I or photosystem II or both
    • In cyclic photophosphorylation, only photosystem I is involved
    • In non-cyclic photophosphorylation, both photosystem I and photosystem II are involved
  • Photosystems are collections of photosynthetic pigments that absorb light energy and transfer the energy onto electrons, each photosystem contains a primary pigment
    • Photosystem II has a primary pigment that absorbs light at a wavelength of 680 nm and is therefore called P680
    • Photosystem II is at the beginning of the electron transport chain and is where the photolysis of water takes place
    • Photosystem I has a primary pigment that absorbs light at a wavelength of 700 nm and is therefore called P700
    • Photosystem I is in the middle of the electron transport chain
  • The energy carried by the ATP is then used during the light-independent reactions of photosynthesis


Alistair graduated from Oxford University in 2014 with a degree in Biological Sciences. He has taught GCSE/IGCSE Biology, as well as Biology and Environmental Systems & Societies for the International Baccalaureate Diploma Programme. While teaching in Oxford, Alistair completed his MA Education as Head of Department for Environmental Systems and Societies.

Join Save My Exams

Download all our Revision Notes as PDFs

Try a Free Sample of our revision notes as a printable PDF.

Join Now
Go to Top