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Active transport - endocytosis a process in which a small...

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Active transport A fourth method for movement across the membrane is  active transport.  When active  transport is taking place, a protein moves a certain material across the membrane from  a region of lower concentration to a region of higher concentration. Because this  movement is happening against the concentration gradient, the cell must expend energy  that is usually derived from a substance called adenosine triphosphate or ATP. An  example of active transport occurs in human nerve cells. Here, sodium ions are  constantly transported out of the cell into the external fluid bathing the cell, a region of  high concentration of sodium. (This transport of sodium sets up the nerve cell for the  impulse that will occur within it later.)  Endocytosis The final mechanism for movement across the plasma membrane is 
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Unformatted text preview: endocytosis, a process in which a small patch of plasma membrane encloses particles or tiny volumes of fluid that are at or near the cell surface. The membrane enclosure then sinks into the cytoplasm and pinches off from the membrane, forming a vesicle that moves into the cytoplasm. When the vesicle contains particulate matter, the process is called phagocytosis. When the vesicle contains droplets of fluid, the process is called pinocytosis. Along with the other mechanisms for transport across the plasma membrane, endocytosis ensures that the internal cellular environment will be able to exchange materials with the external environment and that the cell will continue to thrive and function....
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