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    (Original post by abananapeel)
    one thing that really confuses me are the terms reliability, validity and accuracy, specially when they come on the same question.

    For example some question says comment on the reliability of (a certain given data set) comment on it's validity.

    How would a data set be accurate, reliable, valid?


    accuracy depends on the appratus u use.
    Reliability depends on how many times u've repeated the experiment and got the same average mean value

    Validity = accuracy plus reliabitily

    for example, u might be given a data or a graph and asked to suggest if the data is valid or not. in that case, u check the variation between the mean values, or the error bars. the more difference is there there less valid it is
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    can somebody please help me some doubts?

    1) What is the difference between the T memory cells produced during T helper activation stage and the T memory cells produced during cell mediated response?

    2) and how are these T memory cells different from B memory cells?
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    (Original post by LABONNO)
    You can get it from the site free exam papers.
    I cant access it.
    Do you think you could link it?
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    hey do we have to know about gram staining?
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    (Original post by CONFUSED19)
    I cant access it.
    Do you think you could link it?
    Which papers are you seeking?
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    (Original post by EstebanK0)
    Which papers are you seeking?
    unit 4 biology january 2013
    the one that happened a few months ago
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    how to calculate the efficiency of energy transfer between trophic levels?
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    (Original post by mycollege)
    how to calculate the efficiency of energy transfer between trophic levels?
    Energy used to make biomass / Total energy taken in (from previous trophic level)
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    (Original post by LABONNO)
    Anyone have the topic test answers of Hodder Edexcel A Level BIOLOGY for A2?
    Where can I get them?
    Go here: http://www.dynamic-learning-student.co.uk/
    Register, Log in, then select your book (Bio for A2)
    I think there are links for the answers; not sure though
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    (Original post by raves)
    hey do we have to know about gram staining?
    Know that gram staining can be used to differentiate between gram-positive and gram-negative bacteria.
    Result with gram-positive: Positive, bacteria appear purple in colour
    Result with gram-negative: Negative, bacteria appear red in colour

    I'm not sure whether we have to know the structural differences between gram-positive and gram-negative though
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    Alright! thank youu
    (Original post by SKK94)
    Know that gram staining can be used to differentiate between gram-positive and gram-negative bacteria.
    Result with gram-positive: Positive, bacteria appear purple in colour
    Result with gram-negative: Negative, bacteria appear red in colour

    I'm not sure whether we have to know the structural differences between gram-positive and gram-negative though
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    (Original post by iwantopas19)
    accuracy depends on the appratus u use.
    Reliability depends on how many times u've repeated the experiment and got the same average mean value

    Validity = accuracy plus reliabitily

    for example, u might be given a data or a graph and asked to suggest if the data is valid or not. in that case, u check the variation between the mean values, or the error bars. the more difference is there there less valid it is
    hmm seems clearer than before, thanks!
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    would someone please explain what is genetic drift and founder effect? when do we use them?
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    (Original post by bubblegummer)
    would someone please explain what is genetic drift and founder effect? when do we use them?
    Genetic drift is when the allele frequency of a particular allele increases or decreases within a gene pool. This may result in the loss of a trait or the spread of a trait within a population. However, genetic drift is not due selection pressures resulting in mutations, creating beneficial alleles etc ( at least to my knowledge )
    Now the founder effect, is when uncommon alleles increase in frequency, or when number of different alleles decrease in frequency, within a new population.
    So, in a way, the founder effect may also cause genetic drift within a population (since allele frequencies get changed)

    We could use these concepts to explain loss of genetic variatoin in a population, or speciation.

    Hope I am right, and hope you understand
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    What is clonal selection??
    I'm finding it hard to put in words
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    (Original post by SKK94)
    Genetic drift is when the allele frequency of a particular allele increases or decreases within a gene pool. This may result in the loss of a trait or the spread of a trait within a population. However, genetic drift is not due selection pressures resulting in mutations, creating beneficial alleles etc ( at least to my knowledge )
    Now the founder effect, is when uncommon alleles increase in frequency, or when number of different alleles decrease in frequency, within a new population.
    So, in a way, the founder effect may also cause genetic drift within a population (since allele frequencies get changed)

    We could use these concepts to explain loss of genetic variatoin in a population, or speciation.

    Hope I am right, and hope you understand
    thank you for explaining!
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    could some explain the correlation value and the critical values... it was asked in jan 2013 paper? question 6cii?
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    well clonal selection is the stage of antibodies and killing of pathogen . B effector cells differntiate to produce plasma cells (at this stage there are more RER and golgi body produced) Plasma cells produce large amount of anitbodies and release into blood.
    correct me if im wrong
    (Original post by SKK94)
    What is clonal selection??
    I'm finding it hard to put in words
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    (Original post by raves)
    well clonal selection is the stage of antibodies and killing of pathogen . B effector cells differntiate to produce plasma cells (at this stage there are more RER and golgi body produced) Plasma cells produce large amount of anitbodies and release into blood.
    correct me if im wrong
    You are right about the process.

    But I thought clonal selection had something to do with the specificity of antibodies to antigens?
    I found this link; it may help understand clonal selection...
    http://www.biology.arizona.edu/immun...ology/09t.html
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    oh right thats much better thanks!
 
 
 
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