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bio mcqs..

Discussion in 'International A And AS Level' started by hassam, May 25, 2011.

  1. hassam

    hassam

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    What occurs in the sieve tube elements of a photosynthesising leaf and an actively growing root?
    sieve tube elements in leaf sieve tube elements in root
    A water potential decreases sugars are moved in
    B water potential decreases sugars are moved out
    C water potential increases sugars are moved in
    D water potential increases sugars are moved out

    y anser is B
     
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  3. UAEgurl

    UAEgurl

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    well i think its B because i read this :

    Phloem is a tissue comprising several different cell types, including parenchyma, sclerenchyma fibres,
    and the phloem vessels, called sieve tubes, which are made of sieve-tube elements. Phloem carries sugars (and other photoassimilates) from sources where they are released (eg photosynthesising leaves where they are made,) to sinks
    where they used (eg shaded leaves, storage organs like roots which store the sugars as starch).
    This process is called translocation. It is now known that it is not just the sugars and other solutes that move through the phloem, but the water
    moves with it - the whole phloem sap moves in bulk flow (mass flow or mass transport).

    so it woulb be B as sugars are moved out aswell as water and the water potential will decrease. hope this helped!
     
  4. hassam

    hassam

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    Y its a..it doesnt makes any sense to me
     

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  5. Amna

    Amna

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    percentage transfer of energy means how much of the total energy contained in the "food" is transferred. we know the greatest energy loss occurs between the sun and the primary consumer, so the least percent of energy is transferred. and we know that the energy loss becomes progressively less down the food chain, so the percentage of energy transferred increases down the food chain. so what we're looking for is numbers in ascending order from W towards Z. that's option A. :)
     
  6. Amna

    Amna

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    @UAEgurl but since the root isn't a storage organ here, in fact it's actively growing, therefore using more sugars, shouldn't the sugars be moving in? i don't get why it should be B... i think it should be A :( help?
     
  7. hassam

    hassam

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    that was wat i was thinking
     
  8. Amna

    Amna

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    what year was this question from?
     
  9. hassam

    hassam

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    o/n 2010 i ll chek from er
     
  10. sweetiepie

    sweetiepie

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    can sum1 explain cardiac cycle wid graph..:(
     
  11. Amna

    Amna

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    yeah... and then tell me...
     
  12. UAEgurl

    UAEgurl

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    hmm i guess u guys also have a point...i'll ask my teacher then :/
     
  13. UAEgurl

    UAEgurl

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  14. hassam

    hassam

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    AMNA...sugars will be ov course moved out of sieve tube into the roots since...root is growing and needs sugar for respiration......bt i dont understand water potential part...isnt it that water enters in sieve tube near leaf and hydrostatic pressure is generated...so y water potential decreased
     
  15. sparten

    sparten

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    it is A
     
  16. UAEgurl

    UAEgurl

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    really? u checked the marking scheme?
     
  17. ashcull14

    ashcull14

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    What occurs in the sieve tube elements of a photosynthesising leaf and an actively growing root?
    sieve tube elements in leaf sieve tube elements in root
    A water potential decreases sugars are moved in
    B water potential decreases sugars are moved out
    C water potential increases sugars are moved in
    D water potential increases sugars are moved out
    y B?? Please explain SOMEBODY???
     
  18. Kiki99

    Kiki99

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    I think the answer is B because we're looking at the perspective of the sieve tube element here. Since the root is a sink, sugars will move out from the sieve tube into the root hair cells. And also during translocation, sugars made moves into the sieve tube elements which causes the water potential to decrease as there will be more solutes present in the sieve tube element.

    Please correct me if im wrong :)
     
  19. janedoe

    janedoe

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    Can someone please explain this?
    I'm confused between the last two options.
     

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  20. janedoe

    janedoe

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    Why is option A incorrect? When they have specifically mentioned cell may be 'unable to produce' an enzyme..?
    I understand that build up of lipids suggests that this is a hydrolytic enzyme and so lysosomes is the answer.
    But I don't get why golgi apparatus is invalid?
     

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  21. Shaaaazxx

    Shaaaazxx

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    Why is the answer to this C?
     

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