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    Transpiration??????????????????? ??????????????????????????
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    (Original post by fahimak)
    can sum1 please explain all of transpiration to me???
    I JUST DONT GET IT
    rep will be given
    movement of water up the xylem is explained really well here by rosi M:

    http://www.thestudentroom.co.uk/show...=transpiration


    transpiration is basically the loss of water from the aerial parts of the plant (ie leaves etc)
    - water travels up xylem and into mesophyll tissue by osmosis (see above link)
    - then evaporates out of mesophyll layer into inter-cellular spaces (becomes water vapour)
    - then diffuses down a water vapour potential gradient out of stomatal pores into the air
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    (Original post by giraffegiraffe)
    ok i explained this topic to my friend earlier over email, here it is copy-pasted:

    Ok so when the artery bringing blood from the heart reaches the tissue, it branches off into arterlioles and capiliaries .. and these eventually link up on the other end of the tissue with venules/veins to take blood back to the heart.

    and inside the tissue are all the capillaries which every cell can “access”

    so blood enters the tissue under high pressure (why high pressure? Coz the heart has just contracted (ventricular systole) n this is blood at high pressure from an artery) and this high pressure is called HIGH HYDROSTATIC PRESSURE

    and this high pressure forces some of the blood fluid OUT of the capillaries (the capiliaries have pores in them so are leaky) and this fluid that’s been pushed out of the capillaries is the TISSUE FLUID (it’s the same composition as blood minus all the big molecules like plasma proteins/RBCs etc as they were too big to be pushed thru the capillary pores) and this tissue fluid contains all the 'good stuff' from blood like oxygen, nutrients etc and it bathes the cells of the tissue in this good stuff (o2 etc diffuses into the cells’ membranes from the fluid) which they need for respiration.

    So the tissue uses all this good stuff up, and then by the time we get to the venous end there are 2 things to remember

    1) the blood has lost its Hydrostatic pressure by now therefore has LOW HYDROSTATIC pressure

    2) the tissue fluid doesn’t have any of the plasma proteins etc, remember? (they were too big to get in) SO it has higher water potential than the blood (which has a lower water potential as it has all these plasma proteins etc) …

    So because of the osmotic force of the plasma proteins in the blood AND the hydrostatic pressure of the tissue fluid, the fluid flows back into the capillaries at the venous end

    but… not all the fluid goes back in. some is drained away by the lymphatic system (which has many vessels like capillaries but with valves to prevent backflow) .. this system starts in the tissues and drains excess fluid into larger vessesl which eventually rejoin the main blood system in the chest cavity.

    So its like a drainage system .. so the lymph fluid, as its basically drained tissue fluid (which is kindof like drained blood plasma minus the plasma proteins etc) therefore the lymph fluid is very similar to the tissue fluid but has less o2 and nutrients (as the good stuff has been used up by the cells/tissues.. remember it diffused in) and more waste products, co2, urea etc which diffuses out of the cell. also lymph has more fatty materials which somehow get in the lymph from intestines and some lymphocytes which are white cells (engulf bacteria etc) made by lymph nodes which are little nodes along the lymphatic system, which filter the fluid now and again.

    sorry that was long, hope it helped




    OMG thankyou
    ur a life saver

    gud luck for exam tomorow lol
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    (Original post by billy_h786)
    the partial pressure of oxygen is low in the placenta so the affinity must be high enough to attract all of the o2 out
    Thanks.

    And while you're at it, what is the ROLE of the glycoprotein and the glycolipid?

    It's got something to do with cell signalling hasn't it but I don't know specifically what.
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    (Original post by fahimak)
    can sum1 please explain all of transpiration to me???
    I JUST DONT GET IT
    rep will be given
    transpiration is the loss of water from aerial parts of a plant (i.e. leaf) by evaporation through stomata pores. This creates a transpiration stream which draws water up through xylem vessels in the plant.

    Water is removed from the top of xylem vessels into the mesophyll cells down the water potential gradient. This removal of water from the xylem reduces the hydrostatic pressure at the top, pushing water up the xylem. the attraction of the water molecules to the xylem vessel wall (adhesion), and to other water molecules (cohesion) helps to keep the water flowing up the xylem at all times.

    root pressure is also built up at the bottom of xylem vessels forcing water up.

    transpiration is affected by:

    -temperature (warm conditions, more transpiration)
    -humidity (wet conditions decrease water potential gradient therefore less transpiration)
    -wind (high wind moves water vapour away from leaves quickly, maintaining steep water potential gradient therefore more transpiration)


    hope it helps
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    (Original post by ayesha00)
    transpiration is the loss of water from aerial parts of a plant (i.e. Leaf) by evaporation through stomata pores. This creates a transpiration stream which draws water up through xylem vessels in the plant.

    Water is removed from the top of xylem vessels into the mesophyll cells down the water potential gradient. This removal of water from the xylem reduces the hydrostatic pressure at the top, pushing water up the xylem. The attraction of the water molecules to the xylem vessel wall (adhesion), and to other water molecules (cohesion) helps to keep the water flowing up the xylem at all times.

    Root pressure is also built up at the bottom of xylem vessels forcing water up.

    Transpiration is affected by:

    -temperature (warm conditions, more transpiration)
    -humidity (wet conditions decrease water potential gradient therefore less transpiration)
    -wind (high wind moves water vapour away from leaves quickly, maintaining steep water potential gradient therefore more transpiration)



    hope it helps
    fnx luv
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    (Original post by The Smeezington)
    the spec says you need to know it. breathing rate=number of peaks per minute
    oxygen uptake=decrease in peaks over a period of 1 minute
    I thought oxygen uptake is given by working out the gradient, well that's what my teacher said.
    are you sure?
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    is it likely that those graphs about pressure changes in the heart will come up?

    i dont understand them
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    (Original post by CullenLoverX)
    is it likely that those graphs about pressure changes in the heart will come up?

    i dont understand them
    me too! can someone please explain it? please???
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    Look at graph:
    http://en.wikipedia.org/wiki/File:Ca..._Ventricle.PNG


    does this show that the electrical activity of the heart is directly related to the cardiac cycle. how.
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    what does everyone think the grade boundaries will be? obv, the lower the better but that'll only happen if it's a really hard exam lol so you can't win either way.

    judging by the past papers, i'd say for an A it'll be around 75-78% i'd be quite pleased with that tbh
    means you can lose upto 12-13 marks and still get an A
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    @GIRAFFE
    What happens to the waste urea, co2, etc
    Good post btw
    Guys i wouldnt worry too much on fetal haemoglobin its been up in recent exam
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    Best of luck to everyone taking this exam! Let us know how ya did tomorrow guys
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    Good luck for tomorrow everyone!!!
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    my teacher today said that topics: blood, tissue fluid and lymph + cell cycles + xerophytes will be unlikely to come up on the exam tommorow and transpiration + spirometer and potometer are highly likely so im gona revise that loads lol

    anyway, good look everyone and seriously have a good nights rest...very important!!!

    oh and dont forget ur lucky boxers (boys) and lucky bridget jones nik naks (girls) lol
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    lmao, funny guy and thanks

    gl to everyone!
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    No doubt we will meet again after tomorrow's exam Best of luck folk x
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    i love transpiration
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    (Original post by xMaGic)
    @GIRAFFE
    What happens to the waste urea, co2, etc
    Good post btw
    Guys i wouldnt worry too much on fetal haemoglobin its been up in recent exam
    All the bits the cells secrete out ( urea etc.) are sent back into the blood near the chest cavity. In the blood they get sent out individually from wherever they're supposed to, like the kidneys or for CO2, the lungs.
    Good luck everyone!
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    how are cells produced in meiosis different from mitosis apart from have half as many chromosomes?? (it was a 3marker)???

    also haploid and diploid definitions and homologous chromosomes????
 
 
 
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