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Unformatted text preview: Facilitated diffusion (see above) is like a siphon in that additional energy is not required but it can only allow movement downhill. Movement against a concentration gradient requires energy. The energy is supplied by ATP which is released by breaking a phosphate bond to produce ADP: ATP ADP + P i + energy Cells that use a lot of active transport have many mitochondria to produce the ATP needed. The Sodium-Potassium Pump The sodium-potassium pump uses active transport to move 3 sodium ions to the outside of the cell for each 2 potassium ions that it moves in. It is found in all human cells, especially nerve and muscle cells. One third of the bodys energy expenditure is used to operate the sodium-potassium pump....
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