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    (Original post by jimber)
    Give an account of the role of pigments in the detection of light by flowering plants and animals.
    (Allow three lined pages)
    (Total 10 marks)
    :eek3: :confused:
    I know how to answer this, but I'll write up an answer tomorrow night as I have to concentrate on my two exams tomorrow!
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    Btw guys, this website has 5 past papers for this unit. DO THEM!

    http://www.deberker.com/deberker/Bio...rkschemes.html

    They're old spec, which is virtually exactly the same as new spec.
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    the paper is out of 40 marks only ? [unit 5]
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    (Original post by koop)
    lol wtf only thing i can think of is auxins in plants causing the bending towards light and photoreceptors in animals causing pupil dilation
    Theres also the stuff about phytochromes, how they abosrb red light and change inactive form Pf into active form Pfr, and yadadada
    But mentioning that along with your two points should be enough for the 10 marks aslong as you go into detail.
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    (Original post by skotch)
    Btw guys, this website has 5 past papers for this unit. DO THEM!

    http://www.deberker.com/deberker/Bio...rkschemes.html

    They're old spec, which is virtually exactly the same as new spec.
    Quality, thanks for this mate
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    You know in the spec, one of the points is

    Describe the role animal models have played in developing explanations of human brain development and function, including Hubel and Wiesel's experiments with monkeys and Kittens.

    Does this include explaining why it occurs i.e. synapses being inactive in the closed eye of kittens?
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    ^They can ask us to suggest why. [meaning it's not explicitly in our spec, but using knowledge gained we can suggest explanations]
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    (Original post by jimber)
    Give an account of the role of pigments in the detection of light by flowering plants and animals.
    (Allow three lined pages)
    (Total 10 marks)
    :eek3: :confused:

    from mark scheme:

    1. absorption of light causes changes in/of photosensitive/photoreceptive, pigments

    2.reference to phytochrome (pigments) in plants/leaves

    3. P660/PR and P730/PFR

    4. P660/PR converted to P730/PFR when red light/eq absorbed,P730/PFR converted to P660/PR when far red light absorbed

    5.P730/PFR high during daytime because more red light present in daylight/white light

    6.reference to slow conversion of P730/PFR back to P660/PR in darkness

    7.reference to phytochromes involved in,initiation of germination/flowering/photomorphogenesis

    8.reference to visual pigments/iodopsin/rhodopsin/visual purple in retina of mammals

    9.rhodopsin/visual purple in rod cells

    10.rhodopsin consists of opsin combined with retinal

    11.cis form of retinal, changes to trans form in light

    12.this causes rhodopsin to split

    13.iodopsin thought to be in cone cells

    14.three types of iodopsin respond to different wavelengths

    15.changes in retinal pigments lead to hyperpolarisation/changes in membrane potential
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    We don't have to know about forms of iodopsin or whatever though so don't panic.
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    ..Hi everyone....I am an A-level student & have a Bio exam nxt week.....If anyone has please send me questions and revision notes on the Assessment article and on Bio unit 5....Even possibly Chem Unit 5 stuff....thnx....

    plz send me on my email address [email protected]

    ....thnx.... (",)
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    (Original post by skotch)
    Btw guys, this website has 5 past papers for this unit. DO THEM!

    http://www.deberker.com/deberker/Bio...rkschemes.html

    They're old spec, which is virtually exactly the same as new spec.
    Excellent, ur a G.:cool:
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    Muscles and Respiration D-D-D-D-D-D-OWNNNNNNNNNNNNNN!

    Finished sooner than I though so I will throw into plant responses, brain and brain imaging cos' I'm hardcore like that.
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    PLANT RESPONSES

    Tropisms are growth responses [in plants] where the direction of the growth/movement is determined by the direction of the stimulus. [directional growth movements in response to directional stimuli]

    Positive tropisms - towards stimuli
    Negative - away from stimuli

    Plant growth hormoes/substances:
    AGCEA
    Auxins - involved in shoot elongation
    Gibberellins - involved in flowering and seed germination
    Cytokinnins - involved in cell division and differentiation
    Ethylene/ethene - fruit ripening and flowering
    Abscisic Acid - leaf fall

    IAA, Indoleacetic Acid, involved in photo and geo tropisms. IAA promotes cell elongation/growth in shoots and inhibits it in roots.

    In photo- the IAA accumulates on the shaded sides of shoots&roots and cell elongation occurs there so the shoot bends towards light. For roots, cell elongation is inhibited so the part exposed to light bends downs away from light.

    In geo- the IAA accumulates on the underside of shoots&roots. Shoots curve upwards and roots curve downwards for the same reason as above.


    Phytochromes.

    Plants detect light using photoreceptors called phytochromes. Phytochromes are molcules that absorb light. There are two states: PR and PRF. PR abosrbs red light [wavelength of 660 nm] and PFR absorbs far-red light [wavelength 730 nm].

    Phytochromes are involved in many plant responses e.g. flowering.

    In the presence of red light, PR is quickly converted to PFR.
    In the presence of far-red light, PFR is quickly converted to PR.
    In darkness, PFR is slowly converted to PR.

    During the day, there's more red light. So the rate of conversion of PR --> PFR is greater than the rate of conversion of PFR --> PR. So there's more PFR at any given time during the day. In periods of short nights (e.g. summers), PFR does not get enough time to completely re-convert to PR so it accumulates.

    It's the varying amounts of PR and PFR that trigger and control plant responses. Like in the summer, the high amounts of PFR stimulate flowering in many plants.

    Model answers for this topic:

    1. Absorption of light causes changes in / of photosensitive / photoreceptive, pigments ;
    2. Reference to phytochrome (pigments) in, plants / leaves ;
    3. P660 / PR and P730 / PFR ;
    4. P660 / PR converted to P730 / PFR when red light / eq absorbed, P730 / PFR converted to P660 / PR when far-red light absorbed ;
    5. P730 / PFR high during daytime because more red light present in daylight / white light ;

    6. Reference to slow conversion of, P730 / PFR, back to, P660 / PR, in darkness ;
    7. Reference to phytochromes involved in, initiation of germination / flowering / photomorphogenesis ;
    1. reference to phytochromes;
    2. name two forms {PFR and PR / P730 and P660};
    3. reference to absorption of light (by phytochromes);
    4. conversion of PR to PFR AND reference to red light;
    5. conversion of PFR to PR AND reference to far red light;
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    Gibberellins - involved in flowering and seed germination
    Ethylene/ethene - fruit ripening and flowering
    Abscisic Acid - leaf fall


    Do we need to know about these? I personally have never heard of them! =/
    I know the others though..
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    It's mentioned in CGP... I knew then from GCSE.

    The spec mentioned light detection alonef or plants [and IAA]. So, apparently we don't have to know AGCEA, but makes no difference to me as it's already ingrained in my memory.
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    Back to the Brain and brain imaging techniques. Do one big review of Bio's work from today and move onto redox in Chemistry.
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    Hey Doughy. It's me guest from that chatroom the other day before Bio Unit 4. I think you should set another chat up or use the same one
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    So hows everyone revising for the synoptic section?
    I'm reading over it and making notes on each page summing up the main points but i don't really find its helping.
    Need some inspiration, hit me up with some suggestion guys =P

    Been looking through nearly all the pages and some of these resources are real helpfull guys, keep it up
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    (Original post by skotch)
    Btw guys, this website has 5 past papers for this unit. DO THEM!

    http://www.deberker.com/deberker/Bio...rkschemes.html

    They're old spec, which is virtually exactly the same as new spec.
    Cool is it Unit 6 we want?
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    Unit 5 mate
 
 
 
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