In the light reactions of photosynthesis, Photosystem I receives electrons from the ETC after Photosystem II sends them to the ETC. Then, when Photosystem I receives light, the electron becomes excited and passes the electron back to the ETC. This leads me to my question: In the following question, are both $B$ and $E$ correct?

Which of the following are directly associated with photosystem I?

$A)$ harvesting of light energy by ATP

$B)$ receiving electrons from the thylakoid membrane electron transport chain

$C)$ generation of molecular oxygen

$D)$ extraction of hydrogen electrons from the splitting of water

$E)$ passing electrons to the thylakoid membrane electron transport chain

  • $\begingroup$ What research have you done before asking it here? $\endgroup$ Jan 21, 2017 at 17:16
  • $\begingroup$ @another'Homosapien' Looked online and in two biology textbooks $\endgroup$
    – suomynonA
    Jan 21, 2017 at 17:20
  • $\begingroup$ What answer is it, according to you, and why/why not? $\endgroup$ Jan 21, 2017 at 17:40
  • $\begingroup$ @another'Homosapien' Please read my question first before commenting. Thanks. $\endgroup$
    – suomynonA
    Jan 21, 2017 at 17:42
  • $\begingroup$ You are correct as any college level Biology text should comfirm. Was this a "choose one answer only test"? $\endgroup$
    – bpedit
    Jan 21, 2017 at 23:26

1 Answer 1


It appears the author of the question is trying to use "thylakoid electron transport chain" in an overly specific way. The chain from which PS I receives electrons has far more components and is different from the shorter chain to which PS I passes its electrons. But according to my copy of Biology, Campbell & Reece 7th edition, both are called "electron transport chains" and both reside in, or on, the thylakoid membrane. Perhaps the "directly" in the question refers to the fact that PS I's electron is first captured by a "primary receptor" before being passed to ferredixon, the first member of the chain to which PS I passes electrons. But, again according to Campbell, this primary acceptor is considered part of the photosystem.

I used to teach this stuff. I'd toss out the question.


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