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1. The photosynthetic electron flow

2. the method through which green plants and some other organisms produce nutrients from carbon dioxide and water using sunlight is known as Photosynthesis . In most cases, the green pigment chlorophyll is used in photosynthesis in plants, which produces oxygen as a by-product .

3. KEY WORDS AND DEFINITIONS  NADPH = Nicotinamide adenine dinucleotide phosphate is an essential electron donor in all organisms, and provides the reducing power for anabolic reactions and redox balance. ATP=  Adenosine triphosphate,  is the principal molecule for storing and transferring energy in cells. PLASTOQUINONES (PQ)=  is an electron carrier that plays an essential role in photosynthesis where it is involved in linear and alternative electron flows PQH 2=  Plastoquinone is reduced when it accepts two electrons from photosystem II and two hydrogen cations (H + ) from the stroma of the chloroplast, thereby forming plastoquinol (PQH 2 ). CYTOCHROME B6F= The cytochrome b6f complex is an enzyme found in the thylakoid membrane in chloroplasts of plants, cyanobacteria, and green algae . It   functions to mediate the transfer of electrons and of energy between the two photosynthetic reaction center complexes. FERREDOXIN= Ferredoxin is a small, iron-containing protein which acts as the electron acceptor associated with Photosystem I in photosynthesis 

4. In photosynthesis, Electrons are transferred sequentially between the two photosystems, with photosystem I acting to generate  Nicotinamide Adenine Dinucleotide Phosphate Hydrogen (NADPH)   and photosystem II acting to generate Adenosine triphosphate  ( ATP). Both photosystems have a variety of pigments that aid in the absorption of light energy as well as a unique pair of chlorophyll molecules at the reaction center. P700 refers to the special pair of photosystem I, and P680 to the unique pair of photosystem II.

5. There are two operating modes for photosynthetic electron flow: linear and cyclic.  On the luminal face of photosystem II (PSII), energy from absorbed photons is utilized in linear electron flow to oxidize water.  The oxidized plastoquinone's (PQ) that diffuse into the membrane get the electrons produced by this action after passing via a succession of electron carriers in PS II.  PQ receives protons from the stroma as it reduces to (PQH 2).  When PQH 2 is oxidized, it releases protons into the lumen by giving electrons to the cytochrome b 6 f ( cyt b 6 f) complex . LINEAR ELECTRON FLOW

6.  After passing via plastocyanin (PC) to photosystem I (PS I) then to ferredoxin (Fdx), and finally participating in the reduction of NADP +, a reaction facilitated by the FNR (ferrodoxin:NADP + reductase), the electrons are subsequently sent to each of these molecules in turn.

7. IN ADDITION TO LINEAR ELECTRON FLOW Three important transmembrane complexes—Photosystem II (PSII), the cytochrome b6f complex (cyt bf), and Photosystem I—transfer electrons from water to NADP in the linear mode (PSI).  The Calvin-Benson-Bassham cycle, which fixes CO2 to generate sugars, uses the resulting NADPH.

8. I n cyclic electron flow (CEF), photosystem I is the area where electrons are recycled.  Because of this, a trans thylakoid proton gradient (pH) is produced, which causes the generation of ATP to occur independently of the production of NADPH, raising the ATP/NADPH ratio in the chloroplast.​

9. CYCLIC ELECTRON FLOW Only PSI and cyt bf are involved in cyclic electron transport. Without generating any net reducing equivalents, it uses electron flow to create an electrochemical proton gradient across the thylakoid membrane. It is assumed that cyclic electron flow serves two main purposes:  (1) ATP production There has been much discussion on the stoichiometry of proton pumping and ATP synthesis, but there is now general agreement that linear electron transport alone most likely does not produce enough ATP to balance the ATP: The Calvin-Benson-Bassham cycle consumes NADPH.

10. Cyclic electron flow is probably responsible for filling the gap. A rapidly light-induced production of ATP occurs at the beginning of illumination of a dark-adapted leaf, which is inextricably linked to the occurrence of a cyclic process. (2) Managing light harvesting: Under intense illumination, cyclic electron flow rises, creating a significant proton gradient necessary for the emergence of nonphotochemical quenching (NPQ) within the antenna, shielding PSII from excessive light.

11. CYCLIC ELECTRON FLOW CONTINUED The mechanism underlying cyclic electron flow is still up for debate. There have been several suggested routes: I Plastoquinone reductase (NDH), a mitochondrial complex I homolog, transfers electrons to plastoquinone. The high rate of cyclic electron flow (>100 s1) and the membrane's low concentration of NDH are incompatible. Furthermore, it is clear that plants deficient in the NDH complex can still undergo cyclic electron transport. NDH may, however, mediate a sizable cyclic flow in the presence of dim light. (ii) A putative ferredoxin-quinone reductase (FQR) is responsible for moving electrons from ferredoxin ( Fd ) to plastoquinone. Despite being expected to be highly prevalent, FQR has never been discovered using biochemical or genetic methods. (iii) In line with earlier findings that ferredoxin is capable of mediating cyclic flow in isolated thylakoids, electrons are transferred from ferredoxin to the  cyt  fb complex and from there to plastoquinone.