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    So I know this isnt chemistry specific, but I'm curious as to whether anyone knows this answer..

    Photolysis of H2O in photosynthesis, how the hell does it happen? It's not in our course, it just says "H2O molecules are split into 2H+ and 1/2 O2 in the presence of photons.

    I'm just curious, tried to do some research but there doesnt seem to be much on it, does anyone actually know how this happens?
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    (Original post by ZachDaniels)
    So I know this isnt chemistry specific, but I'm curious as to whether anyone knows this answer..

    Photolysis of H2O in photosynthesis, how the hell does it happen? It's not in our course, it just says "H2O molecules are split into 2H+ and 1/2 O2 in the presence of photons.

    I'm just curious, tried to do some research but there doesnt seem to be much on it, does anyone actually know how this happens?

    http://www.rsc.org/education/teacher...osynthesis.htm

    5 years ago i couldve explained that
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    I've already read that, it has nothing to do with photolysis... It just states H20 > 2H+ and 1/2 O2...
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    (Original post by ZachDaniels)
    I've already read that, it has nothing to do with photolysis... It just states H20 > 2H+ and 1/2 O2...
    It shouldn't do, O-H bond in water is quite strong to be cleaved by visible light(hv)

    homonuclear diatomic has weaker bonds, ie O-O or Cl-Cl bonds, due to lone pair repulsion that weakens the bonding slightly.
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    Yeah exactly and if it just happens, whats to say that a bottle of water doesn't do it when its exposed to UV light, it doesnt make any sense..

    The OH- ion is too unstable to give off the proton, hence why it's PH 7...

    Gah, it's a mystery to me atm..
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    (Original post by ZachDaniels)
    So I know this isnt chemistry specific, but I'm curious as to whether anyone knows this answer..

    Photolysis of H2O in photosynthesis, how the hell does it happen? It's not in our course, it just says "H2O molecules are split into 2H+ and 1/2 O2 in the presence of photons.

    I'm just curious, tried to do some research but there doesnt seem to be much on it, does anyone actually know how this happens?
    • As excited electrons leave PS II to move along electron transport chain, they must be replaced
    • Light energy splits water into protons, electrons and oxygen(Photolysis)

    thats all ive got in my notes
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    Yeah, its porbably way beyond A-Level work, I'm just curious as to how it actually happens, hence the chemistry section :P

    (Well I posted it in both so...)

    Maybe scientists dont actually know yet?

    Edit (its only wikipedia but it sounds plausible) - Photolysis during photosynthesis occurs in a series of light-driven oxidation events. The energized electron (exciton) of P680 is captured by a primary electron acceptor of the photosynthetic electron transfer chain and thus exits photosystem II. In order to repeat the reaction, the electron in the reaction center needs to be replenished. This occurs by oxidation of water in the case of oxygenic photosynthesis. The electron-deficient reaction center of photosystem II (P680*) is the strongest biological oxidizing agent yet discovered, which allows it to break apart molecules as stable as water.[1]

    The water-splitting reaction is catalyzed by the oxygen evolving complex of photosystem II. This protein-bound inorganic complex contains four manganese ions, plus calcium and chloride ions as cofactors. Two water molecules are complexed by the manganese cluster, which then undergoes a series of four electron removals (oxidations) to replenish the reaction center of photosystem II. At the end of this cycle, free oxygen (O2) is generated and the hydrogen of the water molecules has been converted to four protons released into the thylakoid lumen.
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    ^ so that doesn't actually explain how then. lol
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    (Original post by ZachDaniels)
    Yeah, its porbably way beyond A-Level work, I'm just curious as to how it actually happens, hence the chemistry section :P

    (Well I posted it in both so...)

    Maybe scientists dont actually know yet?
    There's certainly a lot of areas that are open to debate, but the basic principles are reasonably well laid down. The light doesn't directly cleave the O-H bond, but rather knocks an electron off a chlorophyl (via a process that is itself pretty complicated.) The best way to look at what happens next is in terms of an equilibrium:

    2H2O <-> 4H+ 4e- O2

    You drive the equilibrium to the right by replacing the chlorophyll electron that has gone down another absurdly complicated energy transfer chain. In terms of how the water is actually cleaved, the mechanism's not certain, but there's definitely a manganese-based catalyst involved. I'll get a possible mechanism posted up in a bit.

    EDIT: Looks like Wiki beat me to it. :p:

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    Things that make you go hmmmm.

    The fact that its the most powerful biological oxidizing agent yet discovered is crazy..

    I mean we're talking about a substance which is in a thylacoid membrane, in a cloroplast, in a palisade cell, in a leaf...

    I'm amazed.. And I thought botanists were all boring tree huggers...
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    An enzyme catalyses it, thats the most I know apart from the stuff in the book
 
 
 
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