Question

In photophosphorylation, under the circumstances when NADP is no longer available as acceptor the electrons are passed to (1) cytochrome-f (2) plastocyanin (3) cytochrome B6 (4) quinone

Answer 1

CytochromeB6 i guess as in cyclic Photophosphorylation

Answer 2

Answer:

In photophosphorylation, when NADP isn't available to be reduced, the electrons are passed to Cytochrome B₆

Explanation:

As we have already studied, photophosphorylation is the process of conversion of ADP to ATP in the presence of sunlight, i.e., by using solar energy.  

Now, in the electron transport pathway, the electron passes from the primary electron acceptor to ferredoxin. In some systems, upon high yield, there is no more NADP left, and instead, there's only NADP⁺, which can't be reduced. In the presence of NADP⁺, which can’t be reduced, the electron-carrying ferredoxin returns to PS I through cytochrome b₆, f, plastoquinone, and then,  plastocyanin. Because this involves only PS I, this is a cyclic process, i.e., the electron emitted returns to the source.

Thus, in the absence of NADP, the reduced ferredoxin transfers its electron first to cytochrome b₆.

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