Page 6 - Chapter 3: Cells and Tissues
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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.
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.
