Electron Flow in Photosynthesis

Z scheme

Explains synergistic function of photosystems

Ferredoxin

Receives excited electrons in the Z scheme

NADP+

Receives excited electrons after Ferredoxin

PC

Replaces electrons in Photosystem I's reaction center

680nm

Wavelength used by PS II's reaction center (P680)

700nm

Wavelength used by PS I's reaction center (P700)

Noncyclic electron flow

Linear transfer of electrons from water to NADP+

Cyclic electron flow

Recycles electrons, drives photophosphorylation

Green algae and land plants

Where cyclic electron flow occurs

Photosystem I

Transfers excited electrons to the electron transport chain in cyclic electron flow

Oxygenic photosynthesis

Critical for evolution due to oxygen release

O2

Almost nonexistent before water oxidation

Ozone layer

Critical for protection from solar radiation

Final e- acceptor in ETCs

Enables generation of significantly more ATP

Both photosystems run at maximum rates

Outcome when both 680nm and 700nm light are available

Linear fashion

Reason for noncyclic electron flow's name

As-needed basis

Occurrence frequency of cyclic electron flow