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

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    (Original post by ScienceGeek3)
    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?
    For species recoginition.
    To find a fertile partner.
    To create a bond to raise a "baby" .

    Definition of tissues.
    Definition of an organ.
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    Q4 Jun 2009,

    Why is the Mass of DNA in the sperm cell a quarter of the mass of DNA in prophase?
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    (Original post by angel1992)
    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
    But the only issue is that the slight difference in the polypeptide chain could for instance cause a change in shape of an enzymes active site, which would mean the substrate of complementary shape can no longer bind and therefore the enzyme would be disfunctional..
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    (Original post by emmaf)
    In mammals after fertilisation, cells divide by mitosis. Suggest how these cells develop into different tissues.
    By cell differentiation, so only certain genes are switched "on". Not sure how much detail we need to know about that?
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    Expecting a HUGE 6 mark at least question on movement of water in plants...dont think its come up yet....know your apoplastic and symplastic pathways! and cohesion tension for good measure
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    (Original post by liviaaa)
    For species recoginition.
    To find a fertile partner.
    To create a bond to raise a "baby" .

    Definition of tissues.
    Definition of an organ.
    A tissue is a group of similar cells working together to perform a specific function.
    An organ is a combination of tissues co-ordinated to perform a variety of functions however they often have one predominant function

    Explain how gas is exchanged in insects.
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    (Original post by Aimo_1)
    Q4 Jun 2009,

    Why is the Mass of DNA in the sperm cell a quarter of the mass of DNA in prophase?
    During prophase, the DNA has just doubled. Therefore the original cell was half of this. So, a gamete sperm cell is half teh original, so a quater of the doubled DNA. Hope that makes sense.
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    In meisosist he amount of chromosomes are halved so why is there meiosis 1 and meiosis 2?

    Originally two homologous chromosomes >>> 1 chromosome in each daughter cell (Meiosis 1)

    why not stop there? :confused:
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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
    If the curve shifts to the right, haemoglobin has a lower affinity for oxygen, it favours unloading oxygen and becomes saturated at higher partial pressures of oxygen. This shift usually happens when there is an increase in carbon dioxide concentration (during exercise) to keep up with the demands for oxygen by quickly respiring cells.

    If the curve shifts to the left, heamoglobin has a higher affinity for oxygen, it favours loading oxygen and becomes saturated at lower partial pressures of oxygen. This shift usually happens in the heamoglobin of organisms at very high or very low altitudes where there isn't a lot of oxygen.

    Fetal heamoglobin has a dissociation curve to the left so it has a high affinity for oxygen, favours loading and becomes saturated at lower partial pressures of oxygen. This is important because there isn't a lot of oxygen in the mother's blood (because the mother uses up most of the oxygen).

    "Normal" heamoglobin loads oxygen when partial pressure is high (e.g. in the lungs) and unloads when partial pressure is low (e.g. in tissues)
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    (Original post by liviaaa)
    During prophase, the DNA has just doubled. Therefore the original cell was half of this. So, a gamete sperm cell is half teh original, so a quater of the doubled DNA. Hope that makes sense.
    the actualy dna doubles at the interphase along with protein synthesis, not prophase, prophase is where the chromosomes widen and the nuclear envelope disappears , i think.
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    (Original post by liviaaa)
    During prophase, the DNA has just doubled. Therefore the original cell was half of this. So, a gamete sperm cell is half teh original, so a quater of the doubled DNA. Hope that makes sense.
    Thanks, how has it doubled btw? Just after DNA Replication?
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    (Original post by liviaaa)
    By cell differentiation, so only certain genes are switched "on". Not sure how much detail we need to know about that?
    It's a two mark question from the chapter 12 assessment in the Nelson Thornes book... i just don't have the mark scheme :[
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    (Original post by ScienceGeek3)
    A tissue is a group of similar cells working together to perform a specific function.
    An organ is a combination of tissues co-ordinated to perform a variety of functions however they often have one predominant function

    Explain how gas is exchanged in insects.
    -Air enters through spiracles
    -Diffuses down a concentration gradient down trachea and then tracheoles
    -Many tracheoles, large surface area
    -Respiration maintains conc. gradient
    -Tracheles carry air close to every cell in the insect - short diffusion pathway

    Name the blood vessels entering and leaving the liver and kidneys.
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    (Original post by Aimo_1)
    Thanks, how has it doubled btw? Just after DNA Replication?
    During S phase of interphase, when the DNA replicates (doubles)
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    (Original post by ScienceGeek3)
    But the only issue is that the slight difference in the polypeptide chain could for instance cause a change in shape of an enzymes active site, which would mean the substrate of complementary shape can no longer bind and therefore the enzyme would be disfunctional..
    yh that is true, but then how would you suggest alleles are part of the same gene because alleles have slightly different polypeptide chains, yet they are part of the same gene, this must mean that the change that creates the allele will give that allele abiltiy to product a different colour yet it would still be the same gene

    overall would it be easier to say the defintion of a gene is that it codes for a particular charcetristic to prevent confusion?
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    (Original post by James A)
    the actualy dna doubles at the interphase along with protein synthesis, not prophase, prophase is where the chromosomes widen and the nuclear envelope disappears , i think.
    That's why I said just doubled. As interphase is before prophase.
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    (Original post by liviaaa)
    During S phase of interphase, when the DNA replicates (doubles)
    Thank's so much, so whenever it's referring to mass of DNA think about replication?

    I'm assuming mass of DNA halves in Telophase because of the cell splitting into two
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    (Original post by ScienceGeek3)
    But the only issue is that the slight difference in the polypeptide chain could for instance cause a change in shape of an enzymes active site, which would mean the substrate of complementary shape can no longer bind and therefore the enzyme would be disfunctional..
    also in the example you gave, an allele would therefore not be produced would it
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    (Original post by liviaaa)
    -Air enters through spiracles
    -Diffuses down a concentration gradient down trachea and then tracheoles
    -Many tracheoles, large surface area
    -Respiration maintains conc. gradient
    -Tracheles carry air close to every cell in the insect - short diffusion pathway

    Name the blood vessels entering and leaving the liver and kidneys.
    Wow, I've never seen a question like that, we need to know specific names of vessels?
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    (Original post by ScienceGeek3)
    Wow, I've never seen a question like that, we need to know specific names of vessels?
    The spec says "Names are required only of the cronary arteries and of blood vessels entering and leaving the heart, liver and kidneys."

    It was the first Q on one of the previous papers?

    Liver - Hepatic Vein/Artery and Hepatic Portal Vein

    Kidneys - Renal Vein / Artery
 
 
 
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