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    So the unit 4 exam is looming and the photosynthesis and respiration section still terrifies me. I'm getting there with respiration but photosynthesis still remains a mystery.

    Can anyone explain light dependant etc in a way I might understand? I'm also a little worried because all my revision guides talk about the cyclic and non cyclic light dependant stage; I haven't been taught this in class, nor is it on the spec... I'm finding it hard to teach myself because I don't know what the heck it's on about!!

    Help meeeeeee thanks
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    (Original post by killerjane)
    So the unit 4 exam is looming and the photosynthesis and respiration section still terrifies me. I'm getting there with respiration but photosynthesis still remains a mystery.

    Can anyone explain light dependant etc in a way I might understand? I'm also a little worried because all my revision guides talk about the cyclic and non cyclic light dependant stage; I haven't been taught this in class, nor is it on the spec... I'm finding it hard to teach myself because I don't know what the heck it's on about!!

    Help meeeeeee thanks

    Okay heres a quick summary:

    Basically a chlorophyll molecule (which is part of photosystem II; but i believe we dont need to know this) absorbs light; this excites an electron within the chlorophyll molecule to a higher energy level. The electron then passes along the electron transport chain; as it does this energy is released because each electron carrier molecule is at an energy level below the previous one hence energy is released via the redox reactions which are occuring as the electrons are passing; the electrons then reach photosystem I (im not sure if we need to know this either); a chlorophyll molecule within this photosystem then absorbs light and the electrons are excited to an even higher energy level before they are finally transferred to an NADP molecule along with a H+ producing reduced NADP. The energy released at the electron transport chain is used to synthesis ATP from ADP and P... and also note that photolysis is occuring.

    This is non-cyclic.

    the cyclic stage is basically when the photosystem I absorbs light and when the electron is excites; is returns to photosystem I instead of being transferred to a NADP molecule. This is normally done to maintain the balance between ATP and reduced NADP because this method only results in the production of ATP and no reduced NADP.

    Hope this helps...
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    Thank you! Very clear explanation!! So your not sure if we need to know about the photosystems? As I said before, it's not mentioned in the spec!
    Is this an explanation of the light dependant reaction? Is the independant one just the calvin cycle?
    Thaaaaanks
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    (Original post by killerjane)
    Thank you! Very clear explanation!! So your not sure if we need to know about the photosystems? As I said before, it's not mentioned in the spec!
    Is this an explanation of the light dependant reaction? Is the independant one just the calvin cycle?
    Thaaaaanks
    lol yay glad it made sense!

    well if your with AQA i havent seen the photosystems mentioned on markschemes however they have been mentioned in questions; anyway i think you'd have to know about them in order to understand the light dependent reaction fully.

    and yes this is the LDR; the light indepedent one is just the calvin cycle which requires the ATP and reduced NADP from the light depedent reaction.
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    (Original post by AdotK)
    Okay heres a quick summary:

    Basically a chlorophyll molecule (which is part of photosystem II; but i believe we dont need to know this) absorbs light; this excites an electron within the chlorophyll molecule to a higher energy level. The electron then passes along the electron transport chain; as it does this energy is released because each electron carrier molecule is at an energy level below the previous one hence energy is released via the redox reactions which are occuring as the electrons are passing; the electrons then reach photosystem I (im not sure if we need to know this either); a chlorophyll molecule within this photosystem then absorbs light and the electrons are excited to an even higher energy level before they are finally transferred to an NADP molecule along with a H+ producing reduced NADP. The energy released at the electron transport chain is used to synthesis ATP from ADP and P... and also note that photolysis is occuring.

    This is non-cyclic.

    the cyclic stage is basically when the photosystem I absorbs light and when the electron is excites; is returns to photosystem I instead of being transferred to a NADP molecule. This is normally done to maintain the balance between ATP and reduced NADP because this method only results in the production of ATP and no reduced NADP.

    Hope this helps...
    Very good, if you need a diagram, wikipedia has a good one here for non-cyclic, but you don't need to know all of the names of the molecules, just basically where ADP->ATP takes place and NADP->reduced NADP occurs, as well as the splitting of water.

    and here is a good one for cyclic
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    how is the second part of the isa theory paper..any suggestion on topics that i shuld revise??please help...
 
 
 
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