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Transcript
How does stuff get in and out of cells? Active and passive transport across the Plasma Membrane (PM) Diffusion and Osmosis 2 categories of transport across PM 1. passive transport: no cell energy required. Moves along a concentration gradient from areas of high concentration to areas of lower concentration. • diffusion • osmosis 2. active transport: requires cell energy because molecules are transported against a concentration gradient Passive Transport 1. Diffusion: net movement of particles from an area of high concentration (overcrowding) to an area of lesser concentration. 2. Osmosis: the diffusion of H2O molecules through the PM. Diffusion (in detail) • All objects in motion have kinetic energy & move in straight line until they collide w/ something else. • 1827: Robert Brown (Scotland) – Studied pollen under microscope – Observed random movements of grains – Called it “Brownian motion” •What happens when you put a drop of food coloring in water? Diffusion (cont.) • The goal is to get as far away from other molecules as possible – From area of “high concentration” to area of “low concentration.” – Eventually the particles will be as far apart from each other as possible Fig 2 • Key terms – Concentration gradient: diffusion cannot occur unless there’s an area of high concentration (overcrowding). – Selective permeability: The phospholipid bilayer of the PM is selective about what passes through by diffusion. OSMOSIS WHAT: Diffusion of H2O molecules from higher concentration to lower concentration. PM lets water pass through. concentration of H2O is higher OUTSIDE the cell than inside the cell so H2O molecules move IN concentration of H2O is higher INSIDE the cell than outside so H2O molecules move OUT increases pressure in the cell and cell may burst Turgor pressure decreases and cell may shrivel up concentration of H2Ois THE SAME inside & outside the cell so there is No Gain or Loss of H2O molecules Turgor pressure stays the same & cell maintains homeostasis Passive Transport (in detail) • Substances can pass through PM because it is permeable. • They move WITH a concentration gradient • They do this via diffusion, osmosis, etc Facilitated Diffusion Membrane protein Carrier (Transport) Proteins