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    • Thread Starter

    im really stuck.
    i need help on these questions:

    1) explain why animals above a certain size or level of complexity require specialised systems for transport and exchange

    2) (a) Describe how materials move within the circulatory system of a vertebrate

    (b) contrast this with how materials are transported in a flatworm or a single celled eukaryote

    c) Identify two exchange sites in a vertebrate

    Think surface area:volume ratio for 1.

    1) Cannot rely on diffusion alone
    2) a) (Closed system) Oxygen, 4 molecules carried by haemoglobin - becomes oxyhaemoglobin, in red blood cells (erythrocytes) in blood. Oxygenated blood travels through arteries (except for the pulmonary artery) dexoygenated blood travels through veins (except pulmonary veins). Blood flow is controlled by heart beat - arteries >> arterioles (both have pulsatile flow) >> veins (no pulsatile flow - have valves etc.) >> capillaries (1 cell diameter lumen) which are adjacent to alveoli. (More/less detail is needed depending on mark scheme I'm guessing :/)
    b) Haven't done anything about flatworm etc. yet... though I think they diffuse materials through their bodies?
    c) Alveoli, (maybe cell membranes?)

    Hopefully this helps, I'm usually alright at biology xD
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