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    EDIT: TO AVOID ANY CONFUSION/PARANOIA I WANT TO LET YOU GUYS KNOW THAT WE ARE DISCUSSING THE EDEXCEL IAL EXAM ON 21ST


    Greetings, people of the internet.I haven't found any threads for the upcoming unit 1 bio exam so thought I should start one on my own..

    How's revision with you guys?How exactly are you preparing for the exam?

    I'm doing past papers right now and I'm going through the notes I made earlier this year...

    Feel free to ask any questions you have in mind <3
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    Do you have any mindmaps you'd like to share?
    That would be really useful
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    Yah ny summarized notes?
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    not gonna start revision until tuesday after economics
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    I can type out summarized points if you can be more specific about what you need,problem is that I don't have a camera I can use at the moment :C
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    Guys :C anyone here?
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    Judging from the last Bio Unit 3 exam, I don't expect this paper to be a breeze. I'm really nervous for this next one :s Past Papers are the only thing I find useful for Bio. I find its good to study from the mark scheme just to see exactly what they're looking for.
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    Does anyone know what the experiment question might be on?
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    (Original post by Alnassenigzig)
    I can type out summarized points if you can be more specific about what you need,problem is that I don't have a camera I can use at the moment :C
    tz k, u dnt hv to go thru all d trouble to type it.. thanx nwy...
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    Are the experiments usually the same format as unit 3 experiments ?can anyone give me papers that have experimental questions ?
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    I just started on Saturday...did 20 chapters so far...


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    Who's doing edexcel? The unit 1 experiments are Daphnia (heart rate and caffeine), Vitamin C contents of juices, Alcohol conc.+ Temperature and their effect on cell membrane permeability & enzymes conc. on the rates of reaction. I've seen enzymes and Daphnia in a lot of the past papers.
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    I have a question, in the messelson and Stahl experiment, why is it that when we grow n15 bacteria in medium with normal n15 nucleotides for TWO generations, why does it only give light and hybrid DNA and not Heavy???.?.
    Can anyone properly explain this whole experiment please
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    (Original post by Fattyma97)
    I have a question, in the messelson and Stahl experiment, why is it that when we grow n15 bacteria in medium with normal n15 nucleotides for TWO generations, why does it only give light and hybrid DNA and not Heavy???.?.
    Can anyone properly explain this whole experiment please
    Posted from TSR Mobile

    Meselson and Stahl's experiment first involved growing E.coli bacteria on a medium with only 15N.

    I am going to guess that you understand why we are using nitrogen isotopes? Anyway, this is so they can grow and reproduce by making DNA, proteins, etc.

    Growing the bacteria on only 15N meant that all of their DNA was dense/ heavy.

    After they allowed the bacteria to grow for a few generations, they moved these bacteria to a medium with 14N.

    After allowing them to grow on this medium for a generation, they tested the DNA and saw that it was hybrid DNA. This is because the DNA molecules of the bacteria now had 1 heavy strand and 1 light strand.

    The bacteria were then allowed to reproduce for another generation. The DNA was then tested and shown to be hybrid and light. Half of the DNA molecules had all light strands, and half had one heavy and one light strand.

    This is experiment was carried out to confirm that DNA replicates semiconservatively.This is when the DNA unzips and each strand acts as a template for new nucleotides to pair up with its bases.

    This experiment disproved the other ideas of how DNA replicates (conservative and dispersive).

    You can do some further research on the internet if you're interested in knowing more details to help get the ideas into your head! .. I often find that extra reading on the net can help! Youtube videos have been a life saver to me too!

    I hope that explanation is okay and not too waffley haha.. Good luck!
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    (Original post by Vetstudent2014)
    Meselson and Stahl's experiment first involved growing E.coli bacteria on a medium with only 15N.

    I am going to guess that you understand why we are using nitrogen isotopes? Anyway, this is so they can grow and reproduce by making DNA, proteins, etc.

    Growing the bacteria on only 15N meant that all of their DNA was dense/ heavy.

    After they allowed the bacteria to grow for a few generations, they moved these bacteria to a medium with 14N.

    After allowing them to grow on this medium for a generation, they tested the DNA and saw that it was hybrid DNA. This is because the DNA molecules of the bacteria now had 1 heavy strand and 1 light strand.

    The bacteria were then allowed to reproduce for another generation. The DNA was then tested and shown to be hybrid and light. Half of the DNA molecules had all light strands, and half had one heavy and one light strand.

    This is experiment was carried out to confirm that DNA replicates semiconservatively.This is when the DNA unzips and each strand acts as a template for new nucleotides to pair up with its bases.

    This experiment disproved the other ideas of how DNA replicates (conservative and dispersive).

    You can do some further research on the internet if you're interested in knowing more details to help get the ideas into your head! .. I often find that extra reading on the net can help! Youtube videos have been a life saver to me too!

    I hope that explanation is okay and not too waffley haha.. Good luck!
    Woah! Gee,that was helpful,I couldn't find the explanation in the revision guide sufficient for me..thanks
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    No problem.. happy to help! Plus, it gets the ideas stuck in my head too!
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    thanks for that
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    I'm taking this exam! Starting to panic a little :/ I really hate the exam layout they always ask stupid questions and it's so full of data interpretation - there's barely any actual biology! Anyway good luck everyone
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    Thanks for the explanation! Appreciate it. Has anyone finished studying unit 1?
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    Can you help me please with my igcse biology external?
    Im not THAT ready ask me hard questions
 
 
 

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