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AQA BIOL2 Biology Unit 2 Exam - 26th May 2011 watch

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    (Original post by ryan02)
    Is the cohesion, in cohesion tension theory, caused by hydrogen bonds or Van der Waals'?
    cos the text book says hydrogen, but i'm sure my teacher told us it was Van der Waals' :/

    and could someone try explain root pressure to me?

    thanks!
    pretty sure it's Hydrogen bonds (they are technically Van der Waals, but it's definitely h bonds.

    When the casparian strip prevents water from entering via apoplast pathway, the water switches to symplast.
    The salts in the endodermis are actively transported into the xylem and this makes a force which helps draw water up the plant. The force is root pressure.
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    (Original post by Jorgeyy)
    Looks pretty good to me, I probably wouldn't even mention the pharynx myself just that water is drawn in and forced out over the gills ^^
    ive never been taught about the pharynx i hope that doesnt come up
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    (Original post by ryan02)
    are they not just the Vena Cava, and the Aorta? otherwise i'm stuck too :/
    Coronary arteries are the arteries that give the heart oxygen. The vena cava brings deoxy blood into the heart and aorta sends oxy blood to the body.
    The coronary arteries come off the aorta and supply the heart with oxygen, the heart doesn't take oxygen as the blood goes through the atrium/ventricles

    does that make sense?
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    (Original post by maymaymo)
    pretty sure it's Hydrogen bonds (they are technically Van der Waals, but it's definitely h bonds.

    When the casparian strip prevents water from entering via apoplast pathway, the water switches to symplast.
    The salts in the endodermis are actively transported into the xylem and this makes a force which helps draw water up the plant. The force is root pressure.
    You may just want to add that due to the endordermal cells actively transporting ions and salts into the xylem, the water potential of the xylem is lowered and therefore water moves into the xylem via osmosis
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    (Original post by ScienceGeek3)
    Hydrogen bonds. Save van der waals for Chemistry :P
    thanks!

    ...just thing is i remember her saying something about van der waals'. cos she knows nothing about chemistry, and spelt it completely wrong :/
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    (Original post by ScienceGeek3)
    You may just want to add that due to the endordermal cells actively transporting ions and salts into the xylem, the water potential of the xylem is lowered and therefore water moves into the xylem via osmosis
    oh yeah, so what does root pressure do then? :confused:
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    The pharynx is not on the syllabus
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    (Original post by jessplease)
    ive never been taught about the pharynx i hope that doesnt come up
    Same but i'll just use what he typed out in my answer if I have too...

    It's not in my textbook or revision guide so I doubt it will lol probs done some external research

    I'd say it's better to stick to syllabus/mark schemes
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    (Original post by maymaymo)
    oh yeah, so what does root pressure do then? :confused:
    You were correct, I was just adding in some details that may gain marks. The whole process creates a root pressure force, which helps to move water up the plant.
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    (Original post by jessplease)
    ive never been taught about the pharynx i hope that doesnt come up
    Jessplease <3 How did i know you'd be here
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    (Original post by maymaymo)
    sorry it's not really clear.
    So originally it's ii,
    then this become Ii iI (during sc replication, the strands separate and become I, i, i and I which are joined by free nucleotides all 15N)
    becoming : II, Ii, iI, II
    this then becomes
    II, II, II, Ii, iI, II, II II
    8 results!

    Sorry late reply, was revising som philosophy and ethics too
    Yayy i get it thanks sooo much
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    I hope it doesn't have a "wtf" question like unit 4 biology did in january.

    However this would be in true aqa style, we had a 15 mark question on Cow ****.
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    Anyone know the answers to these?

    How will the composition of the hepatic portal vein and hepatic vein differ?

    How will the composition of the hepatic artery and hepatic vein differ?
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    (Original post by BeejTheone)
    Jessplease <3 How did i know you'd be here
    loool well you know, doing what i do best
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    (Original post by ksimmi25)
    Anyone know the answers to these?

    How will the composition of the hepatic portal vein and hepatic vein differ?

    How will the composition of the hepatic artery and hepatic vein differ?
    The hepatic portal vein contents will vary according to what has been absorbed in the stomach and intestines. The hepatic artery has oxygenated blood whilst the hepatic vein has de oxygenated blood.
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    anyone know what any of the smaller 3 markers are likely to be?
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    the hardest topics in my opinion are the capillaries and the hepatic vein, anyone know any revision tips for them.....thanks
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    would people agree with me that transpiration is less likely to come up as there was a big bit in it in january??
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    (Original post by DoaaK)
    hate chapter 13.
    It's actually relatively easy when you do lots of practice questions on it as it's mainly learning adaptations which is just regurgitation in the exam. However, it did take about 1.5 weeks to learn fully
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    (Original post by 123456786)
    the hardest topics in my opinion are the capillaries and the hepatic vein, anyone know any revision tips for them.....thanks
    You do not need to revise the hepatic vein, simply know that it is the vein that comes from the liver. With capillaries try to relate them back to their function i.e. one cell thick, made of squamous cells this provides a short diffusion pathway which allows for efficient exchange of materials. Many capillaries provide a large surface area which increases the diffusion of metabolic materials. Narrow lumen which forces red blood cells to squeeze along the side shortening the diffusion pathway even further.
 
 
 
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