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AQA A2 Biol4 January 2012 pre- exam discussion

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    (Original post by AmbitiousMedic)
    :eek: Okay I'm officially worried about what this exam is going to throw at us...
    Well I'm sure 7/8 questions will be totally unrelated to what we have learnt =/ The last question on the paper is usually the one that actually tests your knowledge.
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    (Original post by craig12)
    Well I'm sure 7/8 questions will be totally unrelated to what we have learnt =/ The last question on the paper is usually the one that actually tests your knowledge.
    It's mainly HSW so not much you can actually revise for that, but I think going through past papers and becoming aware of what types of experiments/questions they usually draw upon would be useful. The last ones are the longer ones, I think these shouldn't be too bad because there is only a handful of topics that you can actually spin out for that many marks and so if you're confident with those topics it shouldn't be too much of a problem..
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    (Original post by barzy_j)
    Is ADP 'used' in the electron transport chain? I did a question we got given and it was one of those respiration experiments about isolating a mitochondria. It basically said the levels of O2 dropped once ADP was added. A mark was for saying ADP is used in the electron transport chain. I can't figure how its used in the chain itself? The only time it comes in is where energy is released from the stalked particles. Anyone?
    When electrons are passed down the electron carriers, energy is lost at each stage; this energy is used to combine ADP and Pi to form ATP. Also the chemiosmosis thing (ATP synthase )
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    (Original post by barzy_j)
    Is ADP 'used' in the electron transport chain? I did a question we got given and it was one of those respiration experiments about isolating a mitochondria. It basically said the levels of O2 dropped once ADP was added. A mark was for saying ADP is used in the electron transport chain. I can't figure how its used in the chain itself? The only time it comes in is where energy is released from the stalked particles. Anyone?
    All I can think of is ADP being combined with the inorganic phosphate to produce ATP. This happens as a result of the hydrogen ions diffusing back in to the matrix through ATPase which provides energy for the synthesis of ATP. I guess from there you say, only then can the oxygen combine with those protons (and electrons) to produce water, therefore being used up.
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    I think there will be lots of respiration in this paper. I really hope so - I just can't cope with shrimps AQA..
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    (Original post by barzy_j)
    True, see this is what confuses me. The energy released from the carriers is used to pump hydrogen across by active transport right? or just released as heat of course. It's not used to produce ATP is it? The only time I thought that ATP was produced is after the protons diffuse back (chemiosmosis).

    And going back to the exam question, shall I just ignore it? ADP isnt used in the electron transport chain really? I stupidly thought it might carry the electrons down it but that just happens in redox reactions.
    The pumping and subsequent diffusion of H+ ions is all sort of part of the ETC. The energy released as the electrons pass down the chain is not directly used to combine ADP + Pi but ADP is still used up as a result of this because the energy is used to move H+ ions which then move back again, causing ATP synthase to combine ADP + Pi.

    For the purposes of the question, I would consider the whole process, including H+ pumping and diffusion, to be part of the ETC.
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    (Original post by PatrickD)
    The pumping and subsequent diffusion of H+ ions is all sort of part of the ETC. The energy released as the electrons pass down the chain is not directly used to combine ADP + Pi but ADP is still used up as a result of this because the energy is used to move H+ ions which then move back again, causing ATP synthase to combine ADP + Pi.

    For the purposes of the question, I would consider the whole process, including H+ pumping and diffusion, to be part of the ETC.
    This seems correct
    How are you revising for this? I've pretty much done but still not confident at all
    Stupid HSW
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    (Original post by barzy_j)
    True, see this is what confuses me. The energy released from the carriers is used to pump hydrogen across by active transport right? or just released as heat of course. It's not used to produce ATP is it? The only time I thought that ATP was produced is after the protons diffuse back (chemiosmosis).

    And going back to the exam question, shall I just ignore it? ADP isnt used in the electron transport chain really? I stupidly thought it might carry the electrons down it but that just happens in redox reactions.
    I can see what's confusing you because ADP doesn't directly drive the electron transport chain. But ATP is also produced, like someone has already said above, when electrons release energy as they're passed along the chain.
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    (Original post by PatrickD)
    The pumping and subsequent diffusion of H+ ions is all sort of part of the ETC. The energy released as the electrons pass down the chain is not directly used to combine ADP + Pi but ADP is still used up as a result of this because the energy is used to move H+ ions which then move back again, causing ATP synthase to combine ADP + Pi.

    For the purposes of the question, I would consider the whole process, including H+ pumping and diffusion, to be part of the ETC.
    In my textbook it says that ATP synthesis is also a direct result of the energy released from electrons being passed down the chain. It's like two different things (the pumping of hydrogen ions producing ATP and the energy from electrons producing ATP) happening at the same time
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    (Original post by barzy_j)
    But energy released from carriers chain is only used to make ATP directly in photosynthesis right, not on the inner membrane of a mitochondria.
    hmm, I'm not quite sure, because up until now I've thought of it as two different processes happening in the electron transport chain. Reduced NAD and FAD releasing their protons which are involved in the pumping and ATPase etc and then releasing their electrons which are passed along the chain, releasing enough energy to also stimulate the synthesis of ATP. All of this happens on the inner membrane of the mitochondria, right?

    edit: never mind, looks like I was wrong
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    (Original post by barzy_j)
    I think your book might be summarising it a little too much. I have a text book that says the same but it's not the case. When it says the energy released goes towards making ATP, it's actually talking about all the steps in which protons are pumped and what not. So don't get confused, it never happens DIRECTLY - that's only in photosynthesis.
    Okay thank you!
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    (Original post by juliewho)
    Fantastic, thanks a lot. We seem to have raced through this unit and missed out a lot of the smaller details.



    Unfortunately the question was the other way round, the advantages of natural over artificial, but thanks anyway Adds to my list of pro's/con's!
    no problem
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    (Original post by EffKayy)
    This seems correct
    How are you revising for this? I've pretty much done but still not confident at all
    Stupid HSW
    NGL, I haven't even started. (Well, technically I wrote the definition of 'ecostystem' on Christmas Eve and quickly gave up). I still have three weeks though and I'm planning on starting revision for both biology and physics today; I only did one week of revision last year so hopefully I'll be okay. I always leave things to the last minute though! :eek3:

    (Original post by barzy_j)
    Thanks, that actually makes it a bit better. I'm beginning to think too much and think of the whole thing as separate steps but it's really the same step.
    No problem. You're right in thinking it's a separate step (so if a question asked you to outline the ETC you'd definitely include it as a separte point/couple of points) but in terms of the three main steps in respiration (glycolysis, Krebs cycle [and link reaction], and ETC), it comes under the ETC.
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    anyone got any idea why the grade boundaries are so low? did a paper today and was shocked you only need 39/75 for an A*?
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    (Original post by Patchey1000)
    anyone got any idea why the grade boundaries are so low? did a paper today and was shocked you only need 39/75 for an A*?
    That would be for Jan 2010? But grade boundaries have been consistently rising year on year. So I'd say an A* would be in the 50s this time.
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    Was 57 for jun 11, 52 for jan 11, i guess it will be around 57-60 this time. To be fair i did worse on the papers with lower boundaries so it is fairly accurate
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    (Original post by ps3g4m3r)
    Was 57 for jun 11, 52 for jan 11, i guess it will be around 57-60 this time. To be fair i did worse on the papers with lower boundaries so it is fairly accurate
    How do you know what the grade boundaries are going to be without even seeing the paper...awk
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    (Original post by EffKayy)
    How do you know what the grade boundaries are going to be without even seeing the paper...awk
    he said he'll 'guess it will be around 57-60 this time'

    lolololol
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    (Original post by James A)
    he said he'll 'guess it will be around 57-60 this time'

    lolololol
    Before sitting the paper?
    Wow. Extraordinary
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    (Original post by EffKayy)
    Before sitting the paper?
    Wow. Extraordinary
    yeah if you can guess what topics came up by looking at previous papers, then you can estimate it definetly

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