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    Explain how efficient exchange of substances in the capillaries is linked to
    (i) the rate of blood flow in the capillaries;

    (ii) the structure of capillaries.

    Can anyone pls help with this?

    i) In the capillaries, blood flows very slowly compared to in the rest of the circulatory system. Think about how easy it is for nutrients to diffuse out of capillaries in slow flow compared to fast flow. You could also link this to tissue fluid if you've learnt about that, and how it affects the pressure gradient that leads to its formation and reabsorption.

    ii) Similarly to some other exchange surfaces, they have very thin (1 cell thick) walls, and are very thin (high surface area/volume ratio). This affects the rate of diffusion, explain how. You could also include the fact that they are found in capillary beds in tissues (large amounts of capillaries together in places where nutrients and oxygen are used up quickly). How would it affect the diffusion rate to have the nutrients on one side constantly consumed? This activity also means they would have a large amount of CO2 diffusing into them, how would this affect the hemoglobin and release of oxygen (you may not have learnt this bit yet depending on exam board and how your teachers do the course)?
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