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1 Cellular Transport aOsmosis Osmosis is the diffusion of water molecules across a differentially permeable membrane from a region where water molecules are more concentrated to one where they are less concentrated The transport of water is simple the cell being selectively permeable will allow water through it until an equilibrium is reached and at that time water will flow both in and out of the cell maintaining the equilibrium For example a red blood cell is placed into a isotonic solution which means both the solution and the cell have the same concentration the net movement of water is zero water however does move freely in and out of the cell to maintain the balance bActive Transport In active transport a cell moves materials from an area of low concentration to an area of high concentration this process is the opposite of osmosis or diffusion Active transport requires energy because it is moving against the concentration gradient In active transport the cell uses ATP to remove unwanted materials and to receive needed ones For example a muscle cell wants potassium and wants to get rid of a sodium the cell releases ATP to the pump proteins which results in the cell ejecting the sodium ion and at the same time another receptor cell accepts a potassium which is then released into the cell and the process is repeated until the cell is finished cFacilitated Transport In facilitated transport a molecule that cannot normally pass through into a cell use a carrier protein to gain access and exit Basically this allows a cell to acquire molecules that cannot get through its selectively permeable membrane For example a plant cell requires glucose and the glucose will not fit through the cell membrane A carrier protein in the plasma membrane will accelerate the movement of the glucose and allow it into the cell 2Tropic Levels and The Food
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