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TRANSPORT ACROSS CELL MEMBRANES Transport by Carriers Learning Outcomes B9 - Describe the structure and function of the cell membrane: Describe and compare: facilitated transport and active transport in terms of: Method of transport (use of channel or carrier protein) Use of energy (active vs. passive) Concentration gradient Type / size of molecule transported Review of Membrane Structure What substances can diffuse through the plasma membrane? What substances cannot? What moves in and out of cells by osmosis? What controls this process? What are two types of membrane proteins that assist with transport of substances across the membrane? Transport by carriers Carrier proteins are found within the cell membrane Specific for certain molecules or ions which cannot pass through the membrane by diffusion 2 types: Passive - with the concentration gradient (high to low) -no energy required Active - against the concentration gradient (low to high) – energy (ATP) required Facilitated Transport Facilitated Transport Uses a protein carrier With the concentration gradient Does not require energy Moves molecules that are too large to cross the membrane on their own Examples: glucose, amino acids Also known as facilitated diffusion (why?) Active Transport Active Transport Uses a protein carrier Against the concentration gradient (low to high) Requires energy (ATP) Used to build up a concentration of a substance on one side of the membrane (why might this be necessary?) Examples of active transport: To concentrate iodine in thyroid cells Sodium-potassium pump in nerve, muscle and other cells Movement of salt in or out of cells to drive osmosis (ex. kidneys) Movement of ions to control pH Sodium Potassium Pump.flv Sodium Potassium Pump.flv Proton pump Comparing methods of transport Gap Junctions Some protein channels connect adjacent cells Allow passage of materials from one cell to another Can be active or passive