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Biology_Edexcel_A-snab_Alevel

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  1. the-circulatory-system
    8 主题
  2. diet-and-health
    11 主题
  3. gas-exchange-cell-membranes-and-transport
    8 主题
  4. nucleic-acids
    3 主题
  5. proteins
    10 主题
  6. inheritance
    7 主题
  7. cell-structure-and-organisation
    7 主题
  8. cell-division
    3 主题
  9. reproduction-and-inheritance
    4 主题
  10. differentiation-and-variation
    5 主题
  11. biodiversity
    9 主题
  12. resources-from-plants
    10 主题
  13. ecosystems-and-energy-transfer
    7 主题
  14. photosynthesis
    7 主题
  15. climate-change
    10 主题
  16. evolution
    3 主题
  17. forensics
    3 主题
  18. microorganisms-and-immunity
    11 主题
  19. muscles-and-movement
    3 主题
  20. respiration
    7 主题
  21. homeostasis
    4 主题
  22. exercise
    4 主题
  23. response-to-the-environment
    8 主题
  24. the-brain-behaviour-and-disease
    10 主题
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Fick’s Law of Diffusion

  • Fick’s Law relates the rate of diffusion to the concentration gradient, the diffusion distance and the surface area

  • This relationship can be represented by the following equation, where ∝ means “proportional to”

rate of diffusion proportional to (surface area x concentration difference)divided bythickness of membrane

  • Proportionality means the rate of diffusion will double if:

    • The surface area or concentration difference doubles

    • The diffusion pathway halves

  • Fick’s Law can be written as an equation which can be used to calculate the rate of diffusion

Rate = P x A x ((C1 – C2)divided byT)

  • Where

    • P = A permeability constant that is a quantitative measure of the rate at which a particular molecule can cross a particular membrane

    • A = surface area

    • C1 – C2 = the difference in concentration between two areas

    • T = thickness of the exchange surface

Worked Example

A sample of alveolar epithelium tissue from a mammal is 1.5 straight mum thick and has a surface area of 3 straight mum2. The concentration of oxygen in the alveolus is 1.8 x 10-16 mol straight mum-3 and the concentration of oxygen in the blood is 7.5 x 10-17 mol straight mum-3. The permeability constant for oxygen across alveolar epithelium is 0.012 molecule s-1.

Calculate the rate of diffusion across the section of alveolar epithelium.

Answer:

Step 1: Substitute numbers into the equation

Rate = P x A x ((C1 – C2)divided by T)

Rate = 0.012 x 3 x ((1.8 x 10-16 – 7.5 x 10-17)divided by1.5)

Step 2: Complete the calculation

Rate = 0.012 x 3 x (1.05 x 10-16 divided by1.5)

Rate = 0.012 x 3 x 7 x 10-17
Rate = 2.52 x 10-18 molecules <img alt=”straight mu” data-mathml='<math class=”wrs_chemistry”><semantics><mi mathvariant=”normal”>μ</mi><annotation encoding=”application/vnd.wiris.mtweb-params+json”>{“language”:”en”,”fontFamily”:”Times New Roman”,”fontSize”:”18″}</annotation></semantics></math>’ height=”22″ role=”math” src=”data:image/svg+xml;charset=utf8,%3Csvg%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%22%20xmlns%3Awrs%3D%22http%3A%2F%2Fwww.wiris.com%2Fxml%2Fmathml-extension%22%20height%3D%2222%22%20width%3D%2211%22%20wrs%3Abaseline%3D%2216%22%3E%3C!–MathML%3A%20%3Cmath%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%20class%3D%22wrs_chemistry%22%3E%3Cmi%20mathvariant%3D%22normal%22%3E%26%23x3BC%3B%3C%2Fmi%3E%3C%2Fmath%3E–%3E%3Cdefs%3E%3Cstyle%20type%3D%22text%2Fcss%22%2F%3E%3C%2Fdefs%3E%3Ctext%20font-family%3D%22Times%20New%20Roman%22%20font-size%3D%2218%22%20text-anchor%3D%22middle%22%20x%3D%225.5%22%20y%3D%2216%22%3E%26%23x3BC%3B%3C%2Ftext%3E%3C%2Fsvg%3E” style=”vertical-align:-6px;width:11px;heig