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The outer membrane of a cell, composed of a bilayer of phospholipids in which proteins are embedded.
plasma membrane
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A double layer of phospholipids that forms the basis of all cellular membranes.
phospholipid bilayer
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Net movement of molecules down a gradient from high to low concentration.
diffusion
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The movement of materials across a membrane down a gradient of concentration, pressure, or electrial charge without using cellular energy.
passive transport
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The diffusion of water, dissolved gases, or lipid soluble molecules through the phospholipid bilayer of a cellular membrane.
simple diffusion
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The diffusion of molecules across a membrane, assisted by protein pores or carriers embedded in the membrane.
facilated diffusion
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The diffusion of water across a differentially permeable membrane, normally down a concentration gradient of free water molecules.
osmosis
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The transfer of subatnces across a cell membrane using cellular energy; includes active transport, endocytosis, and exocytosis.
energy-requiring transport
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