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    (Original post by pandoraclaire)
    thank you so much never understood any of that until now XD
    Welcome. If you have any more questions; quote me :]
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    (Original post by ghogho)
    ur welcome
    but there is something to correct!!!
    natural daylight contain mainly RED light!!!
    wait so in the daylight Pfr is converted to Pr and in the dark, Pfr to Pr right?
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    (Original post by i Pav i)
    Explain how the structure of the axon cell membrane is related to the conduction of nerve impulses?! (3 marks)

    help?! aha.
    umm it has sodium pumps and potassium pumps to transfer na and K ions respectively owing to the need of depolarisation or repolarisation
    it is also impermeable to na + ions ( i think)
    due to the phospholipid nature not allowing charged molecules to pass directly thry them !

    xcant think of anything else.
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    what snynoptic topics do we need to know for this exam??
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    (Original post by This Honest)
    (Original post by d_94)
    .
    what do we need to know for this point on the spec,

    'explain the principle of negative feedback in maintaining systems within narrow limits'
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    (Original post by Cleoleo)
    wait so in the daylight Pfr is converted to Pr and in the dark, Pfr to Pr right?
    red light is abosorbed by PR and converted to PFR
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    (Original post by iesians)
    .
    (Original post by ghogho)
    r
    (Original post by d_94)
    ]
    (Original post by This Honest)
    o



    how can genes be switched on and off using DNA transcription factors including hormones??
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    (Original post by ghogho)
    red light is abosorbed by PR and converted to PFR
    In the daylight?
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    (Original post by Cleoleo)
    In the daylight?
    yup
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    (Original post by wam-bam)
    how can genes be switched on and off using DNA transcription factors including hormones??
    with this q, don't you talk about hormones like anabolic and peptide hormones, with peptide they bind to a receptor on the outside of the cell surface membrane and then this initiates a second messenger which initiates transcription because it causes the RNA polymerase and the transcription factors to form a complex and then bind to the promotor region. While anabolic hormones like testosterone bind to the receptor in the cell directly rather than through a second messenger and has the same effect of intiating transcription.

    Although, I'm probs wrong somewhere.
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    (Original post by ghogho)
    yup
    kk so Pr to Pfr in daylight and Pfr back to Pr at night, and then there's short day and long day plants, short day require all the Pfr to be converted back to Pr to cause germination (uninterrupted darkness must be more than 12 hours) and long day require some Pfr for flowering (uninterrupted darkness must be less than 12 hours), that's basically all i know about Pfr and Pr, is there anything missing?
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    (Original post by i Pav i)
    Explain how the structure of the axon cell membrane is related to the conduction of nerve impulses?! (3 marks)

    help?! aha.
    Contains an Na-K protein channel, which allows the movement (diffusion) of ions from outside membrane inside and vice versa.

    These protein channels span the whole of the membrane and without them, ions cannot travel through the membrane due to the phospholipid bilayer being immpermeable.
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    (Original post by Cleoleo)
    kk so Pr to Pfr in daylight and Pfr back to Pr at night, and then there's short day and long day plants, short day require all the Pfr to be converted back to Pr to cause germination (uninterrupted darkness must be more than 12 hours) and long day require some Pfr for flowering (uninterrupted darkness must be less than 12 hours), that's basically all i know about Pfr and Pr, is there anything missing?

    for the shortday plants the PFr inhibits flowering so these plants flower in winter ie short days and long nights ie low level of PFR (long nights allow PFR made during the day to be converted to PR
    for the longday plants : PFR stimulates flowering so these plants flower in summer ie short nights and long day ie hih level of PFR (nights are too short to change all the PFR back to PR.......
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    (Original post by wam-bam)
    what do we need to know for this point on the spec,

    'explain the principle of negative feedback in maintaining systems within narrow limits'
    I think you just need to know that when there's a change from the norm/set point, then the body counteracts the change in the opposite direction and restores it back to this narrow limit (think of it as wave, where if there's a rise from the base line, the body counteracts the change by bringing it back down (in the opposite direction) which is basically what negative feedback is.

    Then know what mechanisms the body uses when the external temp is too cold or too hot. So too hot, means sweat glands are active and when sweat evaporates, it cools you down. Liver lowers metabolic rate, skeletal muscles relax, hair erector muslces relax, vasodilation ... I'm not sure whether it's in the spec to know about shunt vessels but they basically contrict when you're hot, so increased blood flow to the surface. Oh, and the hypothalamus being the thermoregulatory centre and skin receptors detecting change.

    Opposite for when temperature drops + shivering which increases respiration so more heat generated.

    Please quote me if I've forgotten to add details
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    (Original post by bertiejess)
    Contains an Na-K protein channel, which allows the movement (diffusion) of ions from outside membrane inside and vice versa.

    These protein channels span the whole of the membrane and without them, ions cannot travel through the membrane due to the phospholipid bilayer being immpermeable.
    what is the phospholipid bilayer permeable to again?
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    (Original post by wam-bam)
    how can genes be switched on and off using DNA transcription factors including hormones??
    hormones initiate transcription factors in the cell to bind to a promoter region on DNA
    this either INCREASES or DECREASES the rate of transciption of a particular gene.

    if it increases then the transcription factor was an activator
    if it decreases then it was a repressor.
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    (Original post by Cleoleo)
    what is the phospholipid bilayer permeable to again?
    its permeable to carbon dioxide and oxygen kinda stuff ! anything which is not charged and isnt too big.
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    (Original post by iesians)
    hormones initiate transcription factors in the cell to bind to a promoter region on DNA
    this either INCREASES or DECREASES the rate of transciption of a particular gene.

    if it increases then the transcription factor was an activator
    if it decreases then it was a repressor.
    I thought repressor molecules were comoletely differerent things which could attach to the promoter region or the transcription factors themselves, inhibiting transcription?

    so hormones can either turn transcription on or off?
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    (Original post by iesians)
    its permeable to carbon dioxide and oxygen kinda stuff ! anything which is not charged and isnt too big.
    ahh kk thank you

    what synoptic stuff do we need to know?
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    (Original post by Cleoleo)
    I thought repressor molecules were comoletely differerent things which could attach to the promoter region or the transcription factors themselves, inhibiting transcription?

    so hormones can either turn transcription on or off?
    umm nope transcription factors act as repressor or activators
    its in CGP guide page 67.

    and hormones ACTIVATE THE TRANSCRIPTION FACTORS which then act as either represoor or activator ans determine the transcription rate.
 
 
 
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