Electron pathway |
Electrons follow a circular or cyclic pathway, returning to the same chlorophyll molecule |
Electrons follow a linear pathway, moving from water to NADP+ |
Destination of electrons |
Electrons return to Photosystem I |
Electrons move between both Photosystem II and Photosystem I |
Production of ATP |
ATP is produced during cyclic electron flow |
ATP is produced during both Photosystem II and Photosystem I electron transport |
Production of NADPH |
No NADPH is produced |
NADPH is produced in non-cyclic photophosphorylation |
Oxygen evolution |
Lower or absent in cyclic |
Oxygen is evolved as a byproduct of water splitting in Photosystem II |
Role in carbon fixation |
Does not directly contribute to carbon fixation |
Provides NADPH that are crucial for the reduction of carbon dioxide during the Calvin Cycle |
Energy source |
Uses light energy absorbed by Photosystem I chlorophyll |
Utilizes light energy absorbed by both Photosystem II and Photosystem I chlorophylls |
Occur in |
· Common in certain bacteria
· Some photosynthetic algae |
· Plants
· Algae
· Cyanobacteria |