... permeable membrane. The molecules move down a concentration gradient. The rate of diffusion is affected by several factors: 1} The concentration gradient of the substance effects the rate of diffusion. If the concentration is greater between the two regions, then the rate of diffusion is also increased. 2} The distance over which diffusion takes place, the shorter the distance between the two regions of different concentration the greater the rate of diffusion. The rate can then be said directly proportional to the diameter of the organism. 3} the area over which diffusion takes place. The larger the surface area then the more molecules or ions can travel at any one time, therefore the faster the rate of diffusion. 4} Variations in the cells membrane may affect diffusion as well. Diffusion takes place across epithelial layers or cell membranes. For example the greater the number and size of pores in cell membranes the greater the rate ...

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