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    "the human retina contains rods and cones. describe the similarities and diferences between the pigments in these cells and teh ways in which they respond to light"

    this is a 5 mark question, but im not sure whether it applies to stuff about visual acuity. wot do u think?
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    (Original post by orangazhang)
    "the human retina contains rods and cones. describe the similarities and diferences between the pigments in these cells and teh ways in which they respond to light"

    this is a 5 mark question, but im not sure whether it applies to stuff about visual acuity. wot do u think?

    I think in this case u would firstly say that rods contain the pigmment rhodopsin, and cones iodopsin. say that rods r located around the retina but not at the fovea and cones are concentrated at the fovea.
    In light conditions, rhodopsin is broken up into opsin and retinal, it is "bleached" thus in light, u use cones for greatest visual acuity. IN the dark tho, rhodopsin is re-formed and thus u can c in the dark - well, ure vision becomes better.

    It might be worth while sayin that rods are rod shaped and cones are cone shaped - mite pick u up a mark

    hope this helps!
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    mention the difference in the formation of the membrane....cones have membranes that are actually inside the cell whereas rods have a comb effect going on.
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    rhodopsin photodissociates at low light intensities.
    iodopsin photodissociates at high light intensities
    the products of the rhodopsin actually cause hyperpolarisation so no action potential can be generated along the optic nerve, hence in high light intensities they are- to use the technical term - "useless"
    the products of the iodopsin cause a neurotransmitter to be secreted so an action potential is generated in the bipolar cell
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    btw , its definatley geared towards visual accutiy because they both offer different types.
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    cool thanx for all yer help. but visual acuity is not associated with the pigments rhodopsin and iodopsin is it? also how does the membrane affect the way they respond to light? comb structure more suface area?
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    (Original post by LizzyLizzy)
    btw , its definatley geared towards visual accutiy because they both offer different types.

    True true, so although there may be truth in what I said, it's probably completely irrelevant. The Golden Rule (from GCSE English teacher) is RTBQ/ATBQ...read the bloody question, answer the bloody question
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    Visual acuity is due to the number of photoreceptor cells which synapse with one bipolar cell, not the pigments.

    The neurotransmitter secreted by the photoreceptor cells doesn't initiate an action potential, but instead alters the amount of neurotransmitter released by the bipolar cell, which then initiates an action potential in the ganglion cell.
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    Wow i feel daft - what is visual acuity?
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    It's basically the resolution of the image perceived by the brain. Many rod cells synapse with one bipolar cell, so the information is 'averaged' by the brain, which means the perceived image is of lower resolution.
 
 
 
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