匿名
匿名 發問於 科學及數學生物學 · 7 年前

Diffusion rate plz help 20pts!

1. What does it mean by 'diffusion rate'?

2. Will surface area and thickness/diffusion distance affect diffusion rate? How?

1 個解答

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  • 7 年前
    最愛解答

    Diffusion rate refers to the speed of molecules moving/ spreading/ dispersing from an/a area (gas) or solution (liquid) from a higher concentration to an/a area or solution of a lower concentration. It is a passive random movement of molecules that depends on their thermal motion (kinetic energy) to reach equilibrium.

    Accorded to Fick's Law: Diffusion rate is direct proportional to

    surface area x concentration difference / diffusion pathway

    Surface area (S.A) Diffusion pathway (D.P)

    From the equation, the greater the value of S.A and the greater the value of concentration difference will give a greater diffusion rate. And the shorter the D.P, the less in distance the molecules needed to move, the faster it reached equilibrium, the greater diffusion rate.

    As the larger the surface area to volume ratio provide more space for molecules to diffuse (e.g. microvilli in small intestine and alveoli in lungs) and the shorter the diffusion pathway (e.g. thin membrane) the less the molecules needed to move from one area to another.

    So if suface area is small, concentration gradient is low and diffusion pathway is thick, molecules will take longer time to reach equilibrium thereby, the lower the diffusion rate.

    資料來源: Human physiology
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