B1.4 - Diffusion



The spreading out of the particles of a gas, or of any substance in solution.

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Net Movement

The net movement into or out of cells depends on the concentration of particles on each side of the cell membrane.

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Because the particles move randomly, there will be a net (overall) movement from an area of high concentration to an area of lower concentration.

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The difference in concentration between two areas is called the concentration gradient.

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The larger the difference in cnocentration, the faster the rate of diffusion.

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  • The diffusion of oxygen into the cells of the body from the bloodstream as cells are respiring
  • The diffusion of carbon dioxide into actively photosynthesising plant cells
  • The diffusion of simple sugars and amino acids from the gut through cell membranes
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