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    (Original post by ayesha00)
    can anyone describe what happens during G1,G2 and S1 during interphase?
    g1: growth of organelle number
    g2: growth in cell size
    s: synthesis of dna (dna replication)

    basically interphase is the cell getting ready for mitosis. new organelles are made and DNA is replicated and checked for any errors (mutations)
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    (Original post by The Smeezington)
    Can anyone describe the function of the chordae tendineae in the heart and how they carry out the function
    not in the spec i don't think.
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    (Original post by ayesha00)
    can anyone describe what happens during G1,G2 and S1 during interphase?
    G1: growth in cell size, number of organelles increase, number of proteins being made increase
    S: DNA is replicated (still in chromatin form i.e. DNA wrapped around histone proteins)
    G2: Cell grows again, more proteins synthesised and energy reserves are built up
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    (Original post by ayesha00)
    can anyone describe what happens during G1,G2 and S1 during interphase?
    G1- biosynthesis
    G2- replication of DNA
    s1- growth of organelles
    interphase- DNA is replicated
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    (Original post by billy_h786)
    in light microscopes colour stains chemicaly bind to parts of the cellular structure to show e.g. organelles. Different stains bind to different structures in a cell.

    A lead or salt stain must be used in a electron microscope to scatter the electrons and create contrast
    hope it helps
    my book says electron micrographs are always in b&w and colour added afterwards by computer
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    I hate the topic about lymph, tissue fluid and plasma

    cant get my head round it
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    can sum1 please explain all of transpiration to me???
    I JUST DONT GET IT
    rep will be given
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    (Original post by The Smeezington)
    my book says electron micrographs are always in b&w and colour added afterwards by computer
    yup makes sense, thankyou!
    i guess black & white image can be used as "disadvantage of electron microscope" ??

    Do we have to know specific cell/organelle sizes?
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    Apart from the FOETUS having a HIGHER AFFINITY for oxygen, why else is its disassociation curve to the LEFT of the adult disassociaton curve?
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    (Original post by The Smeezington)
    G1: growth in cell size, number of organelles increase, number of proteins being made increase
    S: DNA is replicated (still in chromatin form i.e. DNA wrapped around histone proteins)
    G2: Cell grows again, more proteins synthesised and energy reserves are built up
    thank you
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    kay, i'm looking at papers from 2004/2005 and some of the questions are really worrying me! i know the spec changed etc. but the questions are on the topics we should know, but the wording is really strange to the point i dont understand what the question is asking and just waffle on about nothing. =/

    can someone please reassure me the wording will be how we've seen it in the new spec papers?
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    (Original post by taunt)
    I hate the topic about lymph, tissue fluid and plasma

    cant get my head round it
    same here. i sort of understand it.
    i'm just dreading a question about that coming up in the exam though.
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    the official OCR/Heinemann book is really crap. anyone agree? the max you can get with the info in that book is a C :|
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    (Original post by The Smeezington)
    my book says electron micrographs are always in b&w and colour added afterwards by computer
    yep thats right the electrons create contrast to give an black and white image.

    the lead is used as a stain to attract the electron beam towards the sample and give contrast as u knw the electrons go through the denser parts of the specimen in a TEM to create a 2d image and are bounced of in a SEM to produce a 3d image
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    anyone tell me about transpiration???? please!!!
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    (Original post by taunt)
    I hate the topic about lymph, tissue fluid and plasma

    cant get my head round it

    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
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    Apart from the FOETUS having a HIGHER AFFINITY for oxygen, why else is its disassociation curve to the LEFT of the adult disassociaton curve?
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    (Original post by qasidb)
    Apart from the FOETUS having a HIGHER AFFINITY for oxygen, why else is its disassociation curve to the LEFT of the adult disassociaton curve?
    the partial pressure of oxygen is low in the placenta so the affinity must be high enough to attract all of the o2 out
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    good night and good luck to everyone x
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    (Original post by billy_h786)
    good night and good luck to everyone x
    byee
    good luck x
 
 
 
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