· Light energy is converted to chemical energy in the form of ATP.
· Consist of cyclic photophosphorylation involving only photosystem I and
non-cyclic photophosphorylation involving both photosystems II and I.
· Light energy captured by pigments/light harvesting complexes passed to
special chlorophyll a, causing excitation of electrons to
higher energy level, which is subsequently captured by primary electron acceptor.
· For cyclic photophosphorylation, excited electrons are returned back to
special chlorophyll a (final electron acceptor), after passing down chain of electron carriers and proton pumps.
· For non-cyclic photophosphorylation, Photosystem I receives replacement of
electrons from photosystem II,
· photosystem II receives replacement of electrons from photolysis of water with
production of oxygen as byproduct.
· Excited electrons are passed along a chain of electron carriers of progressively
lower energy level/electron transport chain, energy released used by proton pumps to
pump H+ from stroma into thylakoid space.
· Creating a proton gradient across thylakoid membrane.
· ATP synthase harness proton gradient/proton motive force to generate ATP as
H+ diffuse back into stroma via ATP synthase.
· Chemiosmosis couples energy released from passage of electrons down
electron transport chain to active transport of H+ from stroma into thylakoid space
via proton pumps.
· For non-cyclic photophosphorylation, NADP reductase combines electrons with H+
and NADP+ (final electron acceptor) to form NADPH for use in Calvin cycle.