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Transcript
Movement Across the Membrane Chapter 6, Section 3 Diffusion The net movement of molecules from areas of high concentration to low concentration Only the random motion of molecules is requiredNo Energy!! In a fluid, molecules will diffuse until equilibrium (or balance) is reached. Passive Transport Diffusion of substances across a selectively permeable membrane Carbon dioxide and oxygen freely diffuse across the membrane Water will also pass across the membrane, but often needs the help of a protein Facilitated Diffusion A process in which a transport protein provides a pathway or channel for molecules to pass across the membrane Osmosis The diffusion of water across a selectively permeable membrane Osmosis and Osmotic Pressure Hypotonic Solutions have a LOW salt concentration relative to the cell Isotonic Solutions have a salt concentration EQUAL to the cell Hypertonic Solutions have a HIGH salt concentration relative to the cell How do cells deal osmotic pressure? Cell Wall- prevents plant cells from bursting Contractile Vacuoles- pump out excess water Bathe cells in isotonic/blood solutions Kidneys/Gills remove excess water from blood Active Transport Movement against the concentration gradient that REQUIRES ENERGY!! Exs: protein pumps and transport of large molecules Transport of Large Molecules ENDOCYTOSIS Takes material into the cell within vesicles EXOCYTOSIS Vesicle fuses with plasma membrane and spills contents outside the cell A Summary: Side by Side