Transport of Materials Ac

Transport of Materials Ac - Facilitated diffusion (see...

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Transport of Materials Ac ross Cell Membranes Facilitated Diffusion Facilitated diffusion involves the use of a protein to facilitate the movement of molecules across the membrane. In some cases, molecules pass through channels within the protein. In other cases, the protein changes shape, allowing molecules to pass through. As can be seen below, the protein changes shape and releases the molecule to the side of the membrane that has the lower concentration.
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Additional energy is not required because the molecule is traveling down a concentration gradient (high concentration to low concentration). The energy of movement comes from the concentration gradient. Active Transport Active transport is used to move ions or molecules against a concentration gradient (low concentration to high concentration). Active transport is like a water pump; it uses energy to pump water uphill where a siphon cannot.
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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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Transport of Materials Ac - Facilitated diffusion (see...

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