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CELL TRANSPORT Chapter 8 Passive Transport • Many substances move in & out of the cell using NO ENERGY • This is called Passive Transport • 2 Types: • 1) Simple Diffusion: Move from high conc → low conc • 2) Facilitated Diffusion Facilitated Diffusion • Many molecules are too large to diffuse through lipid bilayer • Instead, they use carrier proteins, which can change shape, to get across • Facilitated Diffusion: diffusion across a cell membrane with help of carrier proteins • Is passive (no energy) • Facilitated Diffusion Active Transport • At times, molecules may have to move against the concentration gradient • Low conc. → High conc. • This REQUIRES ENERGY, and is called Active Transport • 3 Types: • 1) Sodium/Potassium Pumps • 2) Endocytosis • 3) Exocytosis Sodium/Potassium Pump • Transports sodium (Na+) and potassium (K+) against their concentration gradients • Animals need more Na+ outside/more K+ inside • Pump must change shape to fit Na+/K+ • Energy for this comes from ATP in mitochondria • Each cycle = 3 Na+ out and 2 K+ in Endocytosis • Involves folding cell membrane around LARGE molecules to bring into cell in vesicle • Vesicle: membrane- bound organelle containing food & other molecules Endocytosis (con’t) 2 types: Pinocytosis: intake of fluids Phagocytosis: intake of solids Exocytosis • Reverse of endocytosis • Vesicle fuses with cell membrane to release LARGE molecules from cell How Cells Deal with Osmosis • Human cells usually exist in isotonic solutions • Many cells exist in hypotonic solutions • i.e.: paramecia, plants • Water constantly diffuses in • Organisms must get rid of excess H2O • Contractile Vacuole: organelle in paramecia used to pump H2O out • Cell walls keep plant cells from bursting Active and Passive Cell Transport • Cell Transport