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Transcript
Ch. 3 Notes: Membrane Physiology Cellular Physiology: Membrane Transport Membrane Transport – movement of substance into and out of the cell Transport is by two basic methods o Passive transport --no energy is required o Active transport -- the cell must provide metabolic energy Solutions & Transport Solution – homogeneous mixture of two or more components o Solvent – dissolving medium o Solutes – components in smaller quantities within a solution Intracellular fluid – nucleoplasm and cytosol Interstitial fluid – fluid on the exterior of the cell Selective Permeability The plasma membrane allows some materials to pass while excluding others This permeability includes movement into and out of the cell Passive Transport Processes Diffusion -- particles tend to distribute themselves evenly within a solution o Movement is from high concentration to low concentration, or down a concentration gradient Types of diffusion: o Simple diffusion – unassisted processes Solutes are lipid-soluble materials or small enough to pass through membrane pores o Osmosis – simple diffusion of water o Highly polar water easily crosses the plasma membrane Facilitated diffusion -- substances require a protein carrier for passive transport o Filtration -- Water and solutes are forced through a membrane by fluid, or hydrostatic pressure A pressure gradient must exist Solute-containing fluid is pushed from a high pressure area to a lower pressure area Page | 1 Active Transport Processes Transport substances that are unable to pass by diffusion o They may be too large o They may not be able to dissolve in the fat core of the membrane o They may have to move against a concentration gradient Two common forms of active transport o Solute pumping Amino acids, some sugars and ions are transported by solute pumps ATP energizes protein carriers, and in most cases, moves substances against concentration gradients o Bulk transport Exocytosis Moves materials out of the cell Material is carried in a membranous vesicle Vesicle migrates to plasma membrane Vesicle combines with plasma membrane Material is emptied to the outside Endocytosis Extracellular substances are engulfed by being enclosed in a membranous vescicle Types of endocytosis o Phagocytosis – cell eating o Pinocytosis – cell drinking Page | 2