Answer:
Photosystem II electron flow would stop.
Photosystem I electron flow would probably slow down but not stop.
Explanation:
In photosystem II, electron flow is exclusively dependent on pheophytin which transfers electron from the excited reaction-center P680, to cytochrome b₆f complex and then the electrons are transferred to photosystem I via plastocyanin. Any inhibitor of electron passage through pheophytin will thus, ultimately stop electron flow through Photosystem II.
However, in the case of Photosystem I, even if electron flow through pheophytin is inhibited, it has an alternate pathway for electron flow known as the cyclic electron flow. In cyclic electron flow, electrons passing through its reaction-center P700 does not continue to NADP⁺, but is recycled back through cytochrome b₆f complex to plastocyanin and back to P700. Thus, electrons can continue flowing but at a probably slower rate since no new electrons are coming from Photosystem II.
An inhibitor of electron passage through pheophytin would affect electron flow through each of the two photosystems -
In this photosystem, electron flow is completely dependent on pheophytin so if an inhibitor of electron passage through pheophytin there would be no other way for electrons to move and all the electron acceptors in PS II would be reduced very quickly and stop electron flow.
If there is an inhibitor of electron passage through pheophytin there is another path for electron called cyclic electron flow, therefore, the supply of an electron from PS II would be blocked but with the operation of the cyclic pathway some electrons can flow through PS I
Learn more about photosystem:
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