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Brownian Motion

  • Particles are constantly moving due to their kinetic energy.
  • Motion is random.
  • Particles bouncing off each other. 
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  • Net movement of molecules or ions from a region where they are more highly concentrated to one where their concentration is lower. 
  • Passive diffusion means that no metabolic energy is required.
  • It's the difference in concentration that matters, not the concentration.
  • When there is no concentration gradient, dynamic equilibrium is achieved.
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Rate of Diffusion

Three factors that affect the rate of diffusion:

1. Concentration gradient - larger concentration gradient = faster rate.

2. Area over which diffusion takes place - larger exchange surface = faster rate.

3. Thickness of exchange surface - Thinner exchange surface = faster rate. 

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Facilitated Diffusion

  • There are two types of intrinsic proteins - protein channels and carrier proteins.
  • They facilitate diffusion.
  • Protein channels are water filled, they allow ions to diffuse and are selective.
  • Carrier proteins are specific to a small molecule e.g. glucose. 
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