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OCR 2010 A2 Biology Unit 2 - Control, Genome and Environment watch

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    (Original post by Tinkerbelle ♥)
    Can someone go through meiosis and meiosis 2 for me.. in like real simple terms. As simple as possible just so I can get my head round it then I can work through textbook on it. I just can't seem to get my head around chromosome numbers and stuff

    okay so meiosis is when the cells in the reproductive organs divide to produce gametes. because body cells have a diploid (2) number of chromosomes (1 from mum and 1 from dad), gametes need to be haploid so when the haploid sperm fuses with haploid egg you get a zygote with a diploid number of chromosomes...

    before meisois you have interphase -> DNA unravels and replicates so you have 2 copies of each chromosome in a cell (each copy called a chromatid). this looks like an X shape: / and \ are the sister chromatids

    prophase 1: a) chromosomes condense
    b) homologous chromosomes pair up to form bivalents
    crossing over occurs on various points of the bivalent at chiasmata
    c) centrioles move to opp poles, forming the spindle
    d) nuclear envelope breaks donw


    metaphase 1: a) bivalents line up along equator by attaching to the spindle fibres by their centromeres

    anaphase 1: a) spindle contracts, pulling the bivalents apart to opp ends. (one chromosome goes into each end of the cell)

    telophase 1: a) nuclear envelop reforms
    b) cytoplasm divides by cytokinesis to produce 2 haploid daughter cells

    meiosis 2: this has the same process as meiosis 1 but because the daughter cells are haploid they have half the number of chromosomes. so in anaphase, instead of a bivalent separating, its the chromosome that separates; the centromere divides taking each chromatid to opposite ends. then in telophase, you end up with 4 haploid daughter cells

    is that any clearer?
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    (Original post by zoop)
    Hey if anyone could answer this it would be a HUGE help!!

    Compare and contrast the action of synapses and neuromuscular junctions

    Can't find it in my textbook or rev guide!
    neuromuscular junctions:
    ALWAYS acetylcholine neurotransmitter others are various
    always nicotinic cholinergic receptors others are various
    postsynaptic membrane has clefts for AChE (acetylcholinesterase) others are variuos
    postsynapse is muscle rather than another neurone
    have more receptors on post synaptic membrane
    muscle always contracts when stimulated - neurone not necessarily depolarised enough


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    Could someone please help with the specification point 'Explain that conservation is a dynamic process involving management and reclamation
    the textbook is too waffly on this! thankss
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    -double post lag.
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    (Original post by mikey_g)
    Could someone please help with the specification point 'Explain that conservation is a dynamic process involving management and reclamation
    the textbook is too waffly on this! thankss
    The easiest way to think of it:

    -Ecosystems are dynamic, e.g one change affects another such as pred-prey relationships

    -This means conservation methods must be dynamic, i.e. as changes take place in the ecosystem the conservation methods need to be changed to ensure that they aid the ecosystem and have minimal negative impacts

    -Conservation involves reclamation of ecosystems: retaking and repairing lost or damaged ecosystems so that they may be used once more.

    -It also involves management, to ensure that resources can be taken sustainably (i.e. can be harvested year on year) and it doesnt reduce the needs of people to obtain resources in the future.

    Hope that helps.

    Can people tell me what kinda answer they would write for: Explanation of genetic drift causing large changes in small populations.


    Would you just say that chance factors of passing on certain alleles are increased because there is only a small gene pool resulting in large swings of alleles with some alleles possibly being eradicated from the population?
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    my teacher gave us a good website to help with genetics, forgot about it til now

    http://learn.genetics.utah.edu/

    hope it helps somebody
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    (Original post by Falcon91)
    The easiest way to think of it:

    -Ecosystems are dynamic, e.g one change affects another such as pred-prey relationships

    -This means conservation methods must be dynamic, i.e. as changes take place in the ecosystem the conservation methods need to be changed to ensure that they aid the ecosystem and have minimal negative impacts

    -Conservation involves reclamation of ecosystems: retaking and repairing lost or damaged ecosystems so that they may be used once more.

    -It also involves management, to ensure that resources can be taken sustainably (i.e. can be harvested year on year) and it doesnt reduce the needs of people to obtain resources in the future.

    Hope that helps.

    Can people tell me what kinda answer they would write for: Explanation of genetic drift causing large changes in small populations.


    Would you just say that chance factors of passing on certain alleles are increased because there is only a small gene pool resulting in large swings of alleles with some alleles possibly being eradicated from the population?

    I'd say that... There is a larger chance for genetic drift to happen in smaller populations, because mating is more by chance, whereas in large populations, this mating by chance evens out to not have a bigger overall affect. By chance, Allele A is selected for more than allele a due to the smaller chance of random mating occuring. This increases the frequency of the allele in the population, and could lead to speciation, or the loss of some other alleles from the small gene pool.
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    I've been revising Module 2 today and I think I'll be revising until the actual exam at this rate!!

    Has anyone got revision notes on Module 3? Ecosystems is so boring :/
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    (Original post by skatealexia)
    I'd say that... There is a larger chance for genetic drift to happen in smaller populations, because mating is more by chance, whereas in large populations, this mating by chance evens out to not have a bigger overall affect. By chance, Allele A is selected for more than allele a due to the smaller chance of random mating occuring. This increases the frequency of the allele in the population, and could lead to speciation, or the loss of some other alleles from the small gene pool.
    Thanks alexia.
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    Can someone explain body plans in simple terms please??
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    can someone please elaborate on this point?

    (g)
    state that cyclic AMP activates proteins by altering their three-dimensional structure;


    thankieess
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    (Original post by Archen)
    can someone please elaborate on this point?

    (g)
    state that cyclic AMP activates proteins by altering their three-dimensional structure;


    thankieess
    Basically, when proteins are produced not all of them are immediately usable by their molecules/substrate as the sites are not at the fully correct shape. So when cyclic AMP binds, it allows the tertiary structure to become a better fit for its complementary molecules and thus allowing the protein to be 'activated' for use.
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    (Original post by student92)
    Engineering golden rice

    1) 2 genes from a dafodil and 1 gene from a bacterium - Urwinia Udovara are inserted into a Ti plasmid
    2) Plasmid is taken up by the bacterium - Agrobacterium Tumefacien
    3) Gene is introduced to rice embryos
    4) Gene is transcribed and translated in the endosperm - which produces a protein that synthesises a beta-carotene giving the endosperm a yellow/orange colour, hence golden rice.
    Thanks !! Your a Star!
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    hi hope revesion is good-
    i need some help with biotechnology section. . .

    so basiclly there is two ways to replicate dna?
    PCR and using BACs? ????
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    There seem to be more people using this one, so I'll post this here too:

    (origionally posted on the OFFICIAL OCR A2 Biology - F215 thread)

    OK. I don't know if I am being particularly dense, but here goes. (Thins is using page 63 of the heimemann A2 revise biology book)

    Animal cloning - The first method described (superovulation and surrogacy) involves fertilising lots of eggs from one female with lots of different sperm from a desirable male. Now to me, this is not actually true cloning, as no two gametes are genetically identical due to variation during meiosis (bivalents and random assortment and all that jazz). So these are not genetic copies of the maternal specimen. Therefore not clones. Am I being thick, and missing something, or is this actually correct?
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    not sure but i think:
    Just one sperm is needed to fertilise the egg. . . then division begins. . Scientists divide theses dividing cells (stem cells???) into say two to produces two bundle of dividing cells that will grow to two genetically identical organisms
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    Oh yeah... that would make more sense... it's just not worded particularly clearly in the book... Thanks!
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    no promblem,
    yeah i know alot of things is a bit unclear in the text book! do you think you can help me with my question?
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    (Original post by Fabz2k9)
    hi hope revesion is good-
    i need some help with biotechnology section. . .

    so basiclly there is two ways to replicate dna?
    PCR and using BACs? ????
    Yes, I believe thats right, thats the only ways my memory brings anyways . Because the bacs have individual sheared sections, and they are clonised so they grow and multiply the same individual parts of DNA, and PCR is artificial DNA replication.. so I'd say so .
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    Argggh, please help, I was revising epistasis, but I don't understand the difference between 'recessive epistasis' and 'genes working in a complementary fashion'

    In the OCR (purple) biology textbook page 133 Q4 it asks if the whole 'agouti mice/white mice/black mice' thing is an example of recessive epistasis or complementary gene action or both???????????????
 
 
 
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