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    Can anybody clarify this for me:

    Why does interbreeding two organisms with different numbers of chromosomes produce infertile offspring?

    I know that having an uneven number of chromosomes means homologous pairs can't form so meiosis can't occur.
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    (Original post by HeyThereHarry)
    Can anybody clarify this for me:

    Why does interbreeding two organisms with different numbers of chromosomes produce infertile offspring?

    I know that having an uneven number of chromosomes means homologous pairs can't form so meiosis can't occur.
    As you quite rightly say, meiosis cannot occur when bivalents are unable to form. This is because some of the chromosomes will be unable to pair up and thus the separation of homologous chromosomes at Anaphase I cannot happen (as some didn't pair up in the first place).

    Don't doubt yourself, you understand it!
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    (Original post by TheLegalDealer)
    NMJ only has acetylcholine as the neurotransmitter while S has acetylcholine + many others

    S is between 2 neurons while NMJ is between a neuron and muscle

    S requires many action potentials to cause deporisation while the NMJ requires only one
    + S has many enzymes to breakdown the neurotransmitters
    Thanks!

    Although, this is where I am getting confused as at the neuromuscular junction between a sympathetic neurone and an effector the neurotransmitter is noradrenaline? So the NMJ's do use more than just acetylcholine?
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    (Original post by Hilton184)
    At the neuromuscular junction - in other words, the synapse between the postganglionic neurone and the effector, the neurotransmitter is acetylcholine.




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    But what about between the effector and the neurone when that neurone is sympathetic, is the neurotransmitter not then noradrenaline?
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    Does anyone know what the hydrogen acceptors are in anaerobic respiration?
    My textbook is once again confusing me, whilst it says that in mammals pyruvate is the hydrogen acceptor, it says for yeast that ethanol is?

    Does anyone know whether it should be pyruvate and ethanal, or lactate and ethanol?
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    (Original post by Glh96)
    Does anyone know what the hydrogen acceptors are in anaerobic respiration?
    My textbook is once again confusing me, whilst it says that in mammals pyruvate is the hydrogen acceptor, it says for yeast that ethanol is?

    Does anyone know whether it should be pyruvate and ethanal, or lactate and ethanol?

    The hydrogen acceptor is pyruvate for lactate fermentation and ethanal for alcoholic fermentation. I remember an exam question on this and ethanal was the right answer.
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    Guys I know we've still got a few weeks to go but does anyone have any predictions for F214 or F215?
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    (Original post by a123a)
    The hydrogen acceptor is pyruvate for lactate fermentation and ethanal for alcoholic fermentation. I remember an exam question on this and ethanal was the right answer.

    Thanks, it says ethanol in the back but I guess that's just another OCR textbook error!
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    could someone explain this for me please - 'describe how artificial selection has been used to produce bread wheat (Triticum aestivum)'
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    (Original post by Glh96)
    Thanks!

    Although, this is where I am getting confused as at the neuromuscular junction between a sympathetic neurone and an effector the neurotransmitter is noradrenaline? So the NMJ's do use more than just acetylcholine?
    No, it's ACh only.
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    (Original post by AnnekaChan173)
    No, it's ACh only.

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    (Original post by Glh96)
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    at a synapse? Synapses are neurone to neurone. Not at the NMJ, the NMJ is always ACh only.
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    Anyone have any predictions of topics for this years A2 exams?
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    (Original post by bakedbeans247)
    Anyone have any predictions of topics for this years A2 exams?
    Galapagos. I'm so worried.
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    (Original post by Glh96)
    But what about between the effector and the neurone when that neurone is sympathetic, is the neurotransmitter not then noradrenaline?
    You are confusing two different things here.

    Neuromuscular junction I believe is the synapse between a somatic motor neurone and a sarcomere/muscle fibre. This is voluntary controlled. We voluntarily move our arms.

    Sympathetic neurones are part of the autonomic nervous system - involuntary controlled - increase heart rate for example. Noradrenaline released here is not at a neuromuscular junction.

    Neuromuscular junction is between somatic motor neurone and a skeletal muscle.


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    (Original post by AnnekaChan173)
    Galapagos. I'm so worried.
    Just remember habitat destruction, overeploitation of species and introduction of new species, then fill in the rest with facts! E,g. Red quinine tree out competes scalesia tree!
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    (Original post by bbadonde2)
    Just remember habitat destruction, overeploitation of species and introduction of new species, then fill in the rest with facts! E,g. Red quinine tree out competes scalesia tree!
    How do you remember the tree names? So much to revise, so little time
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    Yeah a neuromuscular junction is from neurone to muscle.

    There are also ganglionic synapses at the effectors in the autonomic nervous system. The sympathetic uses noradrenaline as a neurotransmitter at these synopses and the parasympathetic uses acetylcholine



    (Original post by Hilton184)
    You are confusing two different things here.

    Neuromuscular junction I believe is the synapse between a somatic motor neurone and a sarcomere/muscle fibre. This is voluntary controlled. We voluntarily move our arms.

    Sympathetic neurones are part of the autonomic nervous system - part of the autonomic nervous system. Noradrenaline released here is not at a neuromuscular junction.


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    (Original post by AnnekaChan173)
    How do you remember the tree names? So much to revise, so little time
    I base my revision on key points and then fill in with facts. I don't know it just stays in!
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    (Original post by Hilton184)
    You are confusing two different things here.

    Neuromuscular junction I believe is the synapse between a somatic motor neurone and a sarcomere/muscle fibre. This is voluntary controlled. We voluntarily move our arms.

    Sympathetic neurones are part of the autonomic nervous system - involuntary controlled - increase heart rate for example. Noradrenaline released here is not at a neuromuscular junction.

    Neuromuscular junction is between somatic motor neurone and a skeletal muscle.


    Posted from TSR Mobile
    I see what you mean, but sympathetic neurones (regardless of being involuntary) innervate muscles, simply not skeletal ones, hence why sympathetic action is able to increase heart rate, by having an effect on cardiac muscle.

    In this way, these neurones meet muscle cells at a junction, surely this is a neuromuscular junction? If a neuromuscular junction applies only to the junction between somatic motor neurones and muscle fibres then I can see where my confusion has arisen. However, if not, I still can not understand why noradrenaline is being quoted as the neurotransmitter at this junction?
 
 
 
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