Cyclic and non-cyclic photophosphorylation
Electron in photosystem II are excited by a light photon from a magnesium atom in chlorophyll (photoionisation) and join the electron transport chain.
Electrons travelling down the electron transport chain generate energy through a series of redox reactions.
Electrons are replaced in photosystem II by the photolysis of water to produce oxygen and protons.
Electrons travelling through electron transport chain arrive at photosystem I.
Electrons are excited from photosystem I by light energy.
From here, the electrons have 2 options:
Plant lacking ATP/light has wavelength of 700nm:
Electrons will go through the electron transport chain again
CYCLIC PHOTOPHOSPHORYLATION
Movement of electrons down electron transport chain releases energy that is used to actively transport protons from the stroma to the thylakoid space.
Production of NAPDH/light has wavelength of 680nm:
2 electrons and 2 protons will reduce NADP to NADPH.
Protons flow down a proton gradient via chemiosmosis through ATP synthase to produce ATP from ADP and an inorganic phosphate.
NON-CYCLIC PHOTOPHOSPHORYLATION
Similarities | Differences | |
Non-cyclic | Occur in the thylakoid membrane. Produce ATP through chemiosmosis. Both involve the phosphorylation of ATP as a result of light energy. | Light incident on PS II and PS I Light wavelength is 700nm and 680nm Electrons lost from PS II replaced by photolysis Electrons excited from PS I replaced by electrons from PS II. Electrons lost from PS I combine with NADP and protons to form NADPH. NADPH and ATP produced |
Cyclic | Require light photons for photoionisation to occur. Both processes begin with photoionisation of magnesium ions in chlorophyll. | Light incident on PS I Light wavelength is 680nm Only ATP produced (NO NADPH) Same electron returns to PS I after leaving |