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photosynthesis

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photosynthesis

Postby mark2399 » Fri Nov 28, 2008 3:57 am

hi i have a question about this question i have on my homeowk

which statement regarding events in the functioning of photosystem II is false?
A. Light energy excites electrons in an antenna pigment in a photosynthetic unit
B. The excitation is passes along to a molecule of p680 chlorophyll in the photosynthetic unit
C. The p680 chlorophyll donates a pair of protons to NADPH, which is thus converted to NADP+
D. The electron vacancies in p680 are filled by electrons derived from water.
E. The splitting of water yields molecuar oxygen as a by-product.

I thought it might be D becasue i was looking thoug my textbook and it didn't say it derive from water anywhere. could someone try to help me with this?
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Postby MrMistery » Fri Nov 28, 2008 8:20 pm

the false statement is C. Chlorophyll molecules do not donate protons to anything. P680 donates two electrons to the next acceptor in the chain, plastoquinone. Those electrons travel down through the cytochrome chain to plastocianin to eventually rich P700. P700 can donate electrons to NADP+, converting it to NADPH. The protons in this reaction are taken up from the solution, where they are readily available.
Here is a diagram.
http://www.com.univ-mrs.fr/IRD/atollpol ... es/ps3.jpg
Good luck.
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Re: photosynthesis

Postby pushy » Wed Dec 03, 2008 9:25 am

i think C is false, because p680 donats electrons to pq,where as this pq after giving electron to cytochrome(b6f),it accepts proton from the stroma because it dosent have any metal ion just to neutralise/balance it accept protoh from stroma then through vectorial translocation it gives proton(taken from stroma) to lumen,then in lumen proton motive force create because ph decreases due to addition of protons from stroma............my mail id pushpa.pushy@rediffmail.com :lol:
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