Figure 1. A schematic picture of the linear and cyclic electron flow.

Cytochrome b₆f, PS I, plastocyanin and ferredoxin are respectively depicted in orange, red, blue and purple. In linear electron flow (LEF), shown on the left, the different components of the chain are independent entities and the mobile electron carriers, quinones, plastocyanin and ferredoxin, freely shuttle electrons between the membrane-bound complexes and to FNR. On the contrary, in the cyclic electron flow (CEF) mode, supercomplexes are formed, which comprise, among others, cytochrome b₆f and PS I. The formation of these supramolecular edifices is thought to involve the association of the mobile LHCII proteins depicted in green.