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    (Original post by SKK94)
    A species are a group of individuals that have similar similar characteristics and can breed to produce fertile offspring.

    Reproductive isolation is when individuals of a species cannot breed with each other.
    This may be due to a change in structure of reproductive organs, not allowing for sexuag,l reproduction.
    It could also be because individuals in a population were geographically separated, and with time, developed different reproductive cycles or courtship behaviours that do not let them to breed with each other.
    Reproductive isolation is a way that different species are formed.


    Ohhh angel again... hehe thank uuuuu
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    (Original post by Sravya)
    Could someone explain DNA transcription/ translation..including what happens with the exons and the introns..and what is post transcriptional change?
    Eeeep, I could go through DNA transcription/translation but I'm still clueless about the other bit! I'll read through the official textbook and then let you know?

    Heres translation and transcription for now:
    Transcription:
    · Transcription starts when RNA polymerase attaches to the DNA double-helix at the beginning of a gene
    · The hydrogen bonds between the two strands in the gene break, separating the strands, the DNA molecule uncoils at the point
    · One of the strands is then used as a template to make an mRNA copy, the DNA strand is called the antisense strand
    · The RNA polymerase lines up free RNA nucleotides alongside the template strand. Complementary base pairing means that the mRNA strand ends up being a reverse copy of the DNA template strand
    · Once the RNA nucleotides have paired up with their complementary bases on the DNA strand they’re joined together, forming an mRNA molecule
    · The RNA polymerase moves along the DNA, separating the strands and assembling the mRNA strand
    · The hydrogen bonds between the uncoiled strands of DNA re-form once the RNA polymerase has passed by and strands coil back into the double-helix
    · When RNA polymerase reaches a stop codon, it stops making the mRNA and detaches from the DNA
    · The mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm, where translation can take place.

    Translation:
    · The mRNA attaches itself to a ribosome and tRNA molecules carry amino acids to the ribosome
    · A tRNA molecule, with an anticodon that’s complementary to the first codon on the mRNA, attaches itself to the mRNA by complementary base pairing
    · A second tRNA molecule attaches itself to the next codon on the mRNA in the same way
    · The two amino acids attached to the tRNA molecules are joined by a peptide bond.
    · The first tRNA molecule moves away, leaving its amino acid behind
    · A third tRNA molecule binds to the next codon on the mRNA. Its amino acid binds to the first two and second tRNA molecule moves away
    · This process continues, producing a chain of linked amino acids (a polypeptide chain), until theres a stop codon on the mRNA molecule
    · The polypeptide chain (protein) moves away from the ribosome
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    (Original post by Sravya)
    Wha are the argumens against global warming? In terms of why CO2 and Methane dont contribute?
    It depends on the context of the question, but mainly it will have something to do with the data records not going back far enough, how the ways of measuring climate change/CO2 concentrations are not reliable, extrapolating data is not always reliable, or possibly about how some scientists are biased for whatever reason.
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    (Original post by nukethemaly)
    Eeeep, I could go through DNA transcription/translation but I'm still clueless about the other bit! I'll read through the official textbook and then let you know?

    Heres translation and transcription for now:
    Transcription:
    · Transcription starts when RNA polymerase attaches to the DNA double-helix at the beginning of a gene
    · The hydrogen bonds between the two strands in the gene break, separating the strands, the DNA molecule uncoils at the point
    · One of the strands is then used as a template to make an mRNA copy, the DNA strand is called the antisense strand
    · The RNA polymerase lines up free RNA nucleotides alongside the template strand. Complementary base pairing means that the mRNA strand ends up being a reverse copy of the DNA template strand
    · Once the RNA nucleotides have paired up with their complementary bases on the DNA strand they’re joined together, forming an mRNA molecule
    · The RNA polymerase moves along the DNA, separating the strands and assembling the mRNA strand
    · The hydrogen bonds between the uncoiled strands of DNA re-form once the RNA polymerase has passed by and strands coil back into the double-helix
    · When RNA polymerase reaches a stop codon, it stops making the mRNA and detaches from the DNA
    · The mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm, where translation can take place.

    Translation:
    · The mRNA attaches itself to a ribosome and tRNA molecules carry amino acids to the ribosome
    · A tRNA molecule, with an anticodon that’s complementary to the first codon on the mRNA, attaches itself to the mRNA by complementary base pairing
    · A second tRNA molecule attaches itself to the next codon on the mRNA in the same way
    · The two amino acids attached to the tRNA molecules are joined by a peptide bond.
    · The first tRNA molecule moves away, leaving its amino acid behind
    · A third tRNA molecule binds to the next codon on the mRNA. Its amino acid binds to the first two and second tRNA molecule moves away
    · This process continues, producing a chain of linked amino acids (a polypeptide chain), until theres a stop codon on the mRNA molecule
    · The polypeptide chain (protein) moves away from the ribosome
    Thats really good thanks! from what I understand from Post transcriptional change is that. There intros (the parts that dont code for DNA) are spliced out which leaves the extons so you get a strand of mRNA. the exons are joined together in different orders to form different mRNA strands. This means that more than on amino acid sequence can form more than one protein..

    (Original post by Brad0440)
    It depends on the context of the question, but mainly it will have something to do with the data records not going back far enough, how the ways of measuring climate change/CO2 concentrations are not reliable, extrapolating data is not always reliable, or possibly about how some scientists are biased for whatever reason.
    Thats great thanks!!
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    what do you guys need in this module? I need an A to get into uni :L i sat it in jan and got a C. When i did it in jan i just learnt all the different mark scheme answers.. perhaps that was my downfall.. just been learning the CGP guide and doing past papers again..hope it works :L
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    (Original post by Sravya)
    Thats really good thanks! from what I understand from Post transcriptional change is that. There intros (the parts that dont code for DNA) are spliced out which leaves the extons so you get a strand of mRNA. the exons are joined together in different orders to form different mRNA strands. This means that more than on amino acid sequence can form more than one protein..
    The order of the exons doesn't change, but the number does. For example, if there were three exons in the pre-mRNA strand; 1,2 and 3, they could join together as 123, 12, 13 or 23, but NOT as 312 or 32 etc. Not sure if you meant this, but better safe than sorry.
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    What is the basic outline of the specific human response?

    from what i understand
    it is just the phagocyte activates the T cell.
    This is a specific reaction as the antigen has to be complementary to the T cell.
    Once activated the T cell splits into T helper cells and T memory cells and T killer cells.
    The t cells activate the B cells.
    This is again specific as the antigen on the T cell has to form an antigen- antibody complex.
    Once the B cell meets the complementary antigen it differentiates into plasma cells which screte antibodies.
    and memory cells.

    Then the antibodies bind to the bacteria and label them for the macrophage to engulf them via endocytosis.
    Once inside a vaculoe in the machrophage. The macrophage secretes lysosomes which fuse onto the antigen in the vacule and destroy them
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    (Original post by Brad0440)
    The order of the exons doesn't change, but the number does. For example, if there were three exons in the pre-mRNA strand; 1,2 and 3, they could join together as 123, 12, 13 or 23, but NOT as 312 or 32 etc. Not sure if you meant this, but better safe than sorry.
    Thanks!
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    If two organisms can interbreed to produce a hybrid, which is not fertile, are these two organisms of the same species? If not, why?
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    well, i'm gonna fail. :/ i'm resitting from january and i appear to have forgotten everything. so any tips to cramming??
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    (Original post by Brad0440)
    Also, I don't know how useful this is but I've attached some of my revision posters for this exam...
    this is so cute
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    (Original post by nukethemaly)
    Also if its not too much to ask would you mind making something similar for the antibiotics effectiveness experiment?
    I just remembered I had these notes (used them for unit 6 )

    Check out page 13 for the antibiotics experiment
    Attached Images
  1. File Type: pdf A2 Bio Practical Notes .pdf (895.3 KB, 561 views)
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    (Original post by Satta101)
    If two organisms can interbreed to produce a hybrid, which is not fertile, are these two organisms of the same species? If not, why?
    They are NOT a species, because for two individuals to be a species, they must be able to reproduce to make a viable, FERTILE offspring.
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    (Original post by Satta101)
    If two organisms can interbreed to produce a hybrid, which is not fertile, are these two organisms of the same species? If not, why?
    well the definition of species is :

    individuals which can interbreed to produce fertile offspring

    so i guess they are not the same species?
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    (Original post by bhapps)
    well, i'm gonna fail. :/ i'm resitting from january and i appear to have forgotten everything. so any tips to cramming??
    CGP book and do all of the past papers again!
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    If anyone is having trouble understanding this spec point: Explain how one gene can give rise to more than one protein through post-transcriptional changes to messenger RNA

    then I suggest watching this video: http://www.youtube.com/watch?v=zABxAG2u6Dk
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    In the syllabus it says we need to know about the storing of hydrogen in a fuel by combining it with carbon dioxide and realeaseing oxygen into the atmosphere..what does that mean?
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    (Original post by Sravya)
    In the syllabus it says we need to know about the storing of hydrogen in a fuel by combining it with carbon dioxide and realeaseing oxygen into the atmosphere..what does that mean?

    basically hydrogen + carbon dioxide makes glucose



    which is the fuel part




    and to get that hydrogen, water is split by photolysis



    and oxygen is released

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    (Original post by confusedgirl22)
    basically hydrogen + carbon dioxide makes glucose



    which is the fuel part




    and to get that hydrogen, water is split by photolysis



    and oxygen is released

    Thanks a billion
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    (Original post by Sravya)
    In the syllabus it says we need to know about the storing of hydrogen in a fuel by combining it with carbon dioxide and realeaseing oxygen into the atmosphere..what does that mean?
    Its basically about the hydrogen being combined with carbon dioxide to produce glucose (the fuel) during photosynthesis and releasing oxygen as a waste product.

    If I'm wrong, correct me?
 
 
 
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