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In light reaction, plastoquinone facilitates the transfer of electrons from:
In the thylakoid membrane, photoexcited electrons from PS-II (P680) are accepted by pheophytin and passed to Plastoquinone (PQ). Reduced plastoquinol (PQH2) diffuses across the lipid bilayer and transfers electrons to the Cytochrome b6f complex! Mark Option (1) in 5 seconds.
When Photosystem II absorbs red light at 680 nm, electrons in chlorophyll a become excited and jump into an orbit farther from the atomic nucleus. These electrons are picked up by a primary electron acceptor (pheophytin).
From pheophytin, electrons are transferred to plastoquinone (PQ), a mobile lipid-soluble quinone embedded within the thylakoid lipid bilayer. Plastoquinone picks up protons from the stroma to form PQH2.
PQH2 transfers its electrons to the multi-subunit Cytochrome b6f complex while translocating protons across the thylakoid membrane into the lumen, generating a proton gradient.
From Cyt b6f, electrons are carried by Plastocyanin (a copper-containing mobile protein) to PS-I. Thus, Plastoquinone uniquely facilitates electron transfer from PS-II to Cyt b6f complex.
Diagnose every choice: Know exactly why the right option works and why distractors fail.
Factually exact; plastoquinone transfers electrons from the primary acceptor of PS-II down to the Cytochrome b6f complex.
Incorrect; electron transfer from Cytochrome b6f to PS-I is carried out by Plastocyanin (PC), not plastoquinone.
Incorrect; electron transfer from PS-I to NADP+ is mediated by ferredoxin (Fd) and ferredoxin-NADP+ reductase (FNR).
Incorrect; ATP synthase synthesizes ATP driven by the proton motive force (chemiosmosis), not via direct electron transfer from PS-I.
Plastoquinone (PQ) moves electrons from PS-II to Cyt b6f. Plastocyanin (PC) moves electrons from Cyt b6f to PS-I.
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