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Unformatted text preview: Cotransport Active transport uses energy to pump materials across a membrane. A concentration gradient of ions or molecules therefore is a high-energy condition. The ions or molecules will attempt to move back across the membrane under pressure (osmotic pressure). This energy can be used to transport other molecules across the membrane. In the diagram below, energy from ATP is used to produce a concentration gradient of H + . Sucrose can be pumped into cells where the concentration of sucrose is already high by using the energy of a high concentration of hydrogen ions on the outside of a cell. Active transport pumps the hydrogen ions out and certain proteins in the cell membrane allow the hydrogen ions to reenter the cell. As the hydrogen ions force their way through this protein, the energy of reentry is used to pump sucrose into the cell. Endocytosis and Exocytosis These processes are used for materials that are too big to pass through the plasma membrane via protein transport.protein transport....
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