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AQA BIOL2 Biology Unit 2 Exam - 26th May 2011 watch

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    (Original post by emmaf)
    ah ok, but do we need to know the method (injecting animals etc)?
    You need to know the concept behind it which is that antigen binds to the antibody...
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    How do trees pass on alleles? Meiosis or Mitosis? and how?
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    (Original post by ScienceGeek3)
    Go for it
    Function of the cell wall and chloroplasts?
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    PLEASE SOMEBODY help me!

    Show the results of density gradient centrifugation for 3 replications of E.coli beginning with 14N and then transferred to 15N and the opposite way round.

    Can someone explain how to do this - i really don't understand 14N and 15N :/ apart from the fact that 14N is lighter.
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    (Original post by angel1992)
    im basically asking if different alleles give different polypeptide chains, and if they do how can they be for the same gene because one gene codes for one polypeptide chain doesnt it?
    Oh I see, erm well yeah a gene contains the coded information for making polypeptides, so yes, I would assume different forms of a gene go on to make different of polypeptide chains :confused:
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    (Original post by Master S P)
    How do trees pass on alleles? Meiosis or Mitosis? and how?
    Depends on the type of tree. Some will need male/female seeds (meiosis), others can reproduce themselves (mitosis.)
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    (Original post by ksimmi25)
    PLEASE SOMEBODY help me!

    Show the results of density gradient centrifugation for 3 replications of E.coli beginning with 14N and then transferred to 15N and the opposite way round.

    Can someone explain how to do this - i really don't understand 14N and 15N :/ apart from the fact that 14N is lighter.
    Isn't this unit one? :confused:
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    (Original post by emmaf)
    Can someone simply explain immunological response as a way of comparing the relationship between species please? :]
    Basically:

    Animal A's blood (serum) is injected into animal B who produces antibodies at a quick rate.

    The antibodies made by animal B will be specific to the antigens on animal A's somatic (body) cells.

    These are then extracted and mixed with animals C, D, E etc. If the antigen of animal C's cells are similar to that of animal A's , antibodies will bind to them and form a precipitate.

    The more precipitate formed, the more similar the animal's antigens are to animal A's and so the more similar the species are.


    This is my understanding, although don't hold me to it :')
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    (Original post by liviaaa)
    Function of the cell wall and chloroplasts?
    Cell wall provides mechanical strength to the plant and prevent the bursting of the cell due to osmotic pressure..

    Chloroplasts are used in the process of photosynthesis as they contain thylakoids which contain the green photosynthetic pigment cholorophyll. They are also used for maximum light absorption!

    How does the strutcture of starch differ from that of cellulose?
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    (Original post by liviaaa)
    Yes I did, think it went quite well, but didn't like the essay Q that much! Thanks

    --

    Okay..

    2 factors affecting transpiration rates, and how they affect the rate? (4 marks)
    Temperature - increase in kinetic energy increases rate, water pulled up faster? Im not sure how to word this . cohesion tension theory?

    Air movement - the more air movement there is, the more dispersed the humid layer gets so it lowers the water potential in the air. High water potential near stomata? mesophyl layer? Concentration gradient? ?
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    (Original post by Aimo_1)
    You gonna be able to get the question paper for this one?
    i could....but i aint gnna upload or anything after some idiots tried gettin rude
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    (Original post by EffKayy)
    Temperature - increase in kinetic energy increases rate, water pulled up faster? Im not sure how to word this . cohesion tension theory?

    Air movement - the more air movement there is, the more dispersed the humid layer gets so it lowers the water potential in the air. High water potential near stomata? mesophyl layer? Concentration gradient? ?
    For temperature, we were told to write that an increase in temperature increases the kinetic energy of water molecules and so they move faster consequently increasing the rate of evaporation of water from the leaves thus increasing the rate of transpiration..
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    (Original post by ScienceGeek3)
    Cell wall provides mechanical strength to the plant and prevent the bursting of the cell due to osmotic pressure..

    Chloroplasts are used in the process of photosynthesis as they contain thylakoids which contain the green photosynthetic pigment cholorophyll. They are also used for maximum light absorption!

    How does the strutcture of starch differ from that of cellulose?
    Starch is made from a-glucose, cellulose is b-glucose. Cellulose is always long straight unbranches molecules, where as strach can be highly branches (amylopectin.) Starch may also be in a helix shape (amylose) but not cellulose. Starch's glycosidic bonds are the same way around, however in cellulose the bonds rotate by 180 degrees.

    Influence of selective breeding, on genetic diversity?
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    Can anyone summarise all they know about oxygen dissociation curves. It covers like 1 page in my textbook but there have been Qs on it every exam paper
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    (Original post by ScienceGeek3)
    Oh I see, erm well yeah a gene contains the coded information for making polypeptides, so yes, I would assume different forms of a gene go on to make different of polypeptide chains :confused:
    so wouldnt that mean that different alleles are different genes or maybe the differences are so small that they can be classed as the same gne

    ohh so maybe its different versions of the sameish polypeptide chain???
    so say if you had 200 amino acids for a chain and one amino was different the polypeptide chain type would still be the same in this case, just this slight variation give slight difference to the one characteristic?

    overall techincally genes code for one polypeptide chain, but that one polypeptide chain can have many different forms which involve that change of an amino acid which makes a subtle difference on the chain but its still the same chain

    analogy, think of it like a row of maltesers and then you replace it with a square malteser its still the same row just the slight difference
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    (Original post by EffKayy)
    Temperature - increase in kinetic energy increases rate, water pulled up faster? Im not sure how to word this . cohesion tension theory?

    Air movement - the more air movement there is, the more dispersed the humid layer gets so it lowers the water potential in the air. High water potential near stomata? mesophyl layer? Concentration gradient? ?
    Ermm: Temperature increases the rate of transpiration, as the water molecules have more kinetic energy so move away from the leaf faster. This maintains a high concentration gradient, so the rate increases. I think.

    Yeah high water potential is right with the air movement (small water potential gradient). ^
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    (Original post by liviaaa)
    Isn't this unit one? :confused:
    Nope, definetly unit 2 - all to do with semi conservative replication and stuff but I just can't get my head around the drawings and particularly this type of question so really need help!!! :/
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    (Original post by liviaaa)
    Starch is made from a-glucose, cellulose is b-glucose. Cellulose is always long straight unbranches molecules, where as strach can be highly branches (amylopectin.) Starch may also be in a helix shape (amylose) but not cellulose. Starch's glycosidic bonds are the same way around, however in cellulose the bonds rotate by 180 degrees.

    Influence of selective breeding, on genetic diversity?
    Selective breeding reduces genetic diversity as only organisms with desirable characteristics are made to breed and therefore reduces the number of alleles present amongst the organisms.

    Why is courtship behaviour necessary?
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    (Original post by nasira372)
    Can anyone summarise all they know about oxygen dissociation curves. It covers like 1 page in my textbook but there have been Qs on it every exam paper
    Lungs have a high partial pressure of oxygen. In the lungs haemogolbin has a high affinity for oxygen due to the high partial pressure, so the haemoglobin is saturated with oxygen.

    In the respiring tissues, there's a low patial pressure of oxygen. Therefore haemoglobin has a low affinity for oxygen, and unloads the oxygen. The respiration also produces carbon dioxide, which increases the H+ content in the cells, so oxygen is more readily unloaded.

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    In mammals after fertilisation, cells divide by mitosis. Suggest how these cells develop into different tissues.
 
 
 
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