Page 6 - Chapter 3: Cells and Tissues
P. 6

B.- Movement Across the Cell Membrane
               1.- Passive Transport Mechanisms

               Passive transport mechanisms require no input of energy (ATP).
               a) Diffusion is the movement of a substance from an area of greater
               concentration to an area of lesser concentration.





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               b) Facilitated diffusion is the same as diffusion but uses a helper molecule to
               increase the rate of diffusion.
               c) Osmosis is a special case of diffusion using a semipermeable membrane.
               Osmosis involves the diffusion of water from an area with more water to an
               area of less water. The concentrations of a solution are expressed as tonicity.
               Solutions are isotonic, hypotonic, or hypertonic.
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