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    (Original post by amberee)
    yeah only those with the beneficial allele survive and are able to pass on their genes (which have the beneficial allele) and those that don't can't adapt to the environment so they die out because they are outcompeted

    I hope that's right anyway. One of the topics I need more work on ^__^
    Thanks
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    (Original post by Satta101)
    I've seen a question on the Jan 2011 paper, "Describe how the organisms that cause TB are taken up by macrophages", on the mark scheme is mentions the point of 'labelling of bacteria by B lymphocytes/cells', what does this mean?
    B cells label the bacteria as foreign objects and this allows phagocytes to engulf the bacteria. Basically they can recognise the bacteria they need to kill a lot easier.
    I hated that question :unimpressed:
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    (Original post by Volltorb)
    Its actually active artificial immunity, the vaccine can involve either: weakened virus/bacteria (so its harmless); toxin that's been altered into an harmless form; or an actual part of the pathogen containing the antigen (non self) that leads to specific immunity.
    Oops, grave mistake there! Thanks for pointing out; I'll edit it.
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    (Original post by SKK94)
    Vaccinations are a form of artificial active immunity, where the weakened form of a pathogen is injected into the body (the antigens still function though).
    Cells of the immune system can bind to the antigens (provided they have the specific shape on their receptors) and specific antibodies can be made.
    I think in this case, the humoral response occurs( eventually resulting in B memory cells and B effector cells):
    - The B memory cells are able to 'remember' the pathogen - in case of secondary infection
    - The B effector cells become Plasma cells, which then produce the required antibodies.
    Thank you

    I know some questions in unit 4 are quite unpredictable and there're so much to be absorbed... but shall we all predict what topic will be asked this time?
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    Did anyone take this in January? Possibly the worst paper I've ever seen, pure dirt
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    (Original post by murtz14)
    Did anyone take this in January? Possibly the worst paper I've ever seen, pure dirt
    Nope. We did it after in class though as practice, highest mark was a C. It was a horrible horrible paper! Hope we get a decent one next week (YN)
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    (Original post by murtz14)
    Did anyone take this in January? Possibly the worst paper I've ever seen, pure dirt
    I did! I got a C , the smartest person in my class got a D but I know of someone who got an A!
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    An organism consumes 3000kJ of energy.
    - 1000kJ is lost in respiration
    - 2500kJ is lost in excretion
    - 500kJ is laid down as new tissue
    Is GPP = 3000 and NPP = 500 ?? Are the units kJ/m2/year ?
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    This is a synoptic paper right?
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    (Original post by nukethemaly)
    This is a synoptic paper right?
    Not exactly.
    There could be questions on core principles though, from unit 1 and 2, especially for the ecology or DNA chapters

    Edit: I JUST saw a question on mitosis and plant tissues [June 2011]
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    (Original post by SKK94)
    Not exactly.
    There could be questions on core principles though, from unit 1 and 2, especially for the ecology or DNA chapters

    Edit: I JUST saw a question on mitosis and plant tissues [June 2011]
    Hahah, so it is a synoptic paper, because I remember reading somewhere in the examiner report that it is
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    can anyone explain me the difference between hypothesis, observation, prediction and theory?

    Sample question
    Q. The student thought that the behavious and distribution of the woodlice was being influenced by an abiotic factor. Was this:
    a.hypothesis
    b.observation
    c.prediction
    d.theory?

    I was wondering how manipulating the above question would change it to each of the four options as well.
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    I've been doing a few past papers and noticed quite a lot of AS stuff is coming up.

    What AS stuff have you guys revised (besides the questions that have already come up?)
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    (Original post by abananapeel)
    can anyone explain me the difference between hypothesis, observation, prediction and theory?

    Sample question
    Q. The student thought that the behavious and distribution of the woodlice was being influenced by an abiotic factor. Was this:
    a.hypothesis
    b.observation
    c.prediction
    d.theory?

    I was wondering how manipulating the above question would change it to each of the four options as well.
    Hypothesis: The student thought that the behaviours and distribution of the woodlice was being influenced by an abiotic factor.
    Observation: The student noticed that shaded areas of the garden contained more woodlice.
    Prediction: The student predicted that shaded areas of the garden would contain more woodlice
    Theory: Having recorded the temperature and light levels in different areas of the garden and magically managing to control all biotic factors, the student concluded that the behaviours and distribution of the woodlice was being influenced by an abiotic factor.


    Hypothesis is a loose theory, often made before the experiment that doesn't have much evidence behind it.
    Observation is what you hear/smell/taste/see when an experiment is being carried out.
    Prediction is what you think is going to happen.
    Theory is why the result of the experiment happened having investigated it well.

    Hope that helped
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    (Original post by Helena Kennedy)
    I've been doing a few past papers and noticed quite a lot of AS stuff is coming up.

    What AS stuff have you guys revised (besides the questions that have already come up?)
    Cellulose structure came up in a past paper which I had completely forgot about, so revising starch and cellulose
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    Go over transcription/translation, seems to come up in almost every topic grrr. Last years exams asked for a lot of AS knowledge so beware


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    RNA - What do we need to know about this exactly please?

    &

    Wth is a Cistron? Are they Intons & Extrons? :L
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    (Original post by amberee)
    B cells label the bacteria as foreign objects and this allows phagocytes to engulf the bacteria. Basically they can recognise the bacteria they need to kill a lot easier.
    I hated that question :unimpressed:

    just to confirm, it s both B cells and macrophages that can label the antigen in order to genertae specific antibodies , right? or not....?
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    (Original post by Trinitybabe)
    just to confirm, it s both B cells and macrophages that can label the antigen in order to genertae specific antibodies , right? or not....?
    Yep that's correct
    the difference is that activated T helper cells bind to the B cell APC, and to the macrophage T helper cell binds IN ORDER TO produce clones of active T helper cells and clone of T memory cells
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    (Original post by Volltorb)
    Stimulated B cells> B effector cells> Plasma cells> antibodies.
    The B cells (indirectly) lead to antibodies being produced, these antibodies bind to specific antigens on the bacteria (labelling them). this labeling, therefore allows macrophages and other phagocytes to identity them more quickly.
    ok i m confused now does 'labelling' implies that only the antibodies synthetised by b cells aggregate to their matching antigens , making a complex easier to be detected and engulfed by phagocyte?.....
 
 
 
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