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Transcript
Active Transport, Diffusion and Osmosis Passive Transport by Diffusion • Diffusion is the movement of molecules from an area of high concentration to an area of low concentration.(down the concentration gradient) • Diffusion does not refer only to movement across a membrane. How Diffusion Works • http://highered.mcgrawhill.com/sites/0072495855/student_view0/ chapter2/animation__how_diffusion_works .html Passive Transport by Osmosis • Osmosis is the movement of water across a biological membrane. • Water molecules move from an area of low concentration solute (hypotonic) to an area of high concentration (hypertonic) • Water moves because the membrane is impermeable to the solute Affect of Osmosis http://www.etomica.org/app/modules/sites/Osmosis_old/Background1.html Affect of Osmosis http://en.wikipedia.org/wiki/User:Reo_On/Passive_transport How Osmosis works • http://highered.mcgrawhill.com/sites/0072495855/student_view0/ chapter2/animation__how_osmosis_works .html Passive transport by Facilitated Diffusion • Molecules can enter a cell by diffusion through a specific channel proteins or carrier proteins embedded in the membrane • This process mediated by a membrane protein is called facilitated diffusion • Molecules move down the concentration gradient Channel Proteins • Form highly specific channel through the cell membrane • Permit the passage of ions or polar molecules • Some channel proteins remain open all the time, others have gates that can be opened or closed to allow or prevent the passage of particles http://www.biologycorner.com/APbiology/cellular/(notes)cell_membrane.html Carrier Proteins • Bind to specific molecules, transport them across the membrane and release them • Carrier molecules change shape while transporting molecules • Usually transport ions or small polar molecules but can also transport amino acids and glucose • Have a lower rate of diffusion than channel proteins Channel and Carrier Proteins http://www.ncbi.nlm.nih.gov/books/NBK9928/ • http://highered.mcgrawhill.com/sites/0072495855/student_view0/ chapter2/animation__how_facilitated_diffu sion_works.html Active Transport • Active transport is the movement of ions, molecules or minerals from an area of low concentration to an area of high concentration(against the concentration gradient) • This requires energy in the form of ATP Primary Active Transport • Uses ATP directly to move molecules or ions from one side of the membrane to the other • Ion pumps are carrier proteins that pump ions against the concentration gradient • The sodium-potassium pump pumps Na+ out of the cell and K+ ions into the cell http://saddlebackphysio.blogspot.com/2010/09/membrane-transportjust-passin-through.html How the Sodium-Potassium pump works • http://highered.mcgrawhill.com/sites/0072495855/student_view0/ chapter2/animation__how_the_sodium_po tassium_pump_works.html Secondary Active Transport • As an ion pump functions, a difference in charge, or electrical potential, builds up across the membrane • One side of the membrane gains a more positive or negative charge compared to the other side due to the accumulation of positive or negative ions Secondary Active Transport • The combination of concentration gradient and electrical potential is called an electrochemical gradient • This gradient stores potential energy that can be used by the cell • This energy is used by another protein to transport other molecules across a membrane Electrochemical Gradient http://bioap.wikispaces.com/Ch+7+Collaboration+2010 http://www.cetbiology.com/support/biology-photographs.html Membrane-Assisted Transport • Macromolecules are too large to cross the cell membrane through a channel or by means of a carrier protein • Cells form vesicles to surround incoming or outgoing material and move it across the cell membrane • Membrane-assisted transport requires energy Endocytosis • The process where a cell engulfs material by folding the cell membrane around it and then pinching it off to form a vesicle inside • There are three methods: – Pinocytosis – Phagocytosis – Receptor-mediated endocytosis Receptor-mediated Endocytosis http://www.yellowtang.org/cells.php Pinocytosis http://www.yellowtang.org/cells.php Phagocytosis http://www.yellowtang.org/cells.php Exocytosis • Macromolecules and other large particles leave a cell by exocytosis • Vesicles that contain cell products to be released or waste products to be excreted fuse with the cell membrane and empty their contents into the extracellular environment http://www.linkpublishing.com/video-transport.htm Phagocytosis • http://highered.mcgrawhill.com/sites/0072495855/student_view0/ chapter2/animation__phagocytosis.html