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Edexcel Additional Science Biology - DIFFUSION

• Message 1. 

  Posted by U15626221 (U15626221) on Friday, 22nd February 2013

  I am absolutely stuck on the part of diffusion, could someone please explain clearly and in detail the process of 'diffusion'. I heard this topic always comes up in the exams therefore i would appreciate an answer asap. Thank You

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• Message 2

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  Posted by U15220226 (U15220226) on Friday, 22nd February 2013

  Diffusion is the passive movement of particles from an area of higher concentration to an area of lower concentration. This is the standard description of diffusion in leaves.

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• Message 3

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  Posted by U15626221 (U15626221) on Friday, 22nd February 2013

  Thanks, if you know much about gas exchange explaining that too would help, thanks.

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  Posted by U15220226 (U15220226) on Friday, 22nd February 2013

  The diffusion of gas and the exchange of liquid over a(n imaginary) barrier is pretty much the same. As far as gas exchange occurring in humans, this takes place over cell membranes - These have adapted to become extremely efficient and hold the cell together nicely. Though, diffusion in animal cells will mean that the gas will be let in and out depending on the concentration difference.
  Rate of diffusion depends on 3 things (GCSE relevant):
  - Distance, across the partially permeable membrane
  - Surface area, of the membrane
  - And Concentration difference
  

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• Message 5

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  Posted by The Bitesize Science Teacher (U14392404) on Friday, 22nd February 2013

  In the lungs:
  
  - the concentration of oxygen in the alveoli is greater than its concentration in the blood, so oxygen diffuses into the blood;
  
  - the concentration of carbon dioxide in the blood is greater than its concentration in the alveoli, so carbon dioxide diffuses out of the blood.
  
  This is called gas exchange because, overall, oxygen goes into the blood and carbon dioxide comes out of it.
  
  
  

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