12 Membrane Function Boundary Separates Two Environments Selectively PermeablePassive TransportSimple DiffusionFacilitated DiffusionActive TransportProtein PumpsEndocytosis / Exocytosis
13 Selectively Permeable Membranes and their proteins allow only certain molecules to crossDiffusion: movement of a substance from an area of high concentration to low concentrationOsmosis: movement of water from an area of low solute concentration to high
16 Passive TransportThe movement of a molecule across a membrane from high to low concentrationMolecules move with the concentration gradientSimple DiffusionNo proteins neededFacilitated DiffusionMembrane proteins required
17 Simple DiffusionSmall, uncharged molecules can move directly across membraneIncludes gases (CO2 and 02 ) and water
18 Facilitated Diffusion Uses either protein channels or transporters (change shape)Channel Transporter
20 Active TransportMovement of molecules across a membrane from low concentrations to highMolecules move against the concentration gradientRequires a protein transporter (pump) and energy supplied by ATPEx. sodium/potassium pump
24 EndocytosisCell membrane surrounds and engulfs food particle or extra-cellular fluidResults in vesicle inside cellPhagocytosis: engulfing large particles like bacteriaPinocytosis: engulfing extra-cellular fluid and whatever it might contain
30 Review QuestionsName 5 types of membrane proteins and describe their functionsWhat is the most significant difference between passive and active transport?Why are transport proteins necessary in facilitated diffusion?Why does active transport require energy?
31 Problems#1The internal cell concentration of sucrose is 1M, the external concentration is .1M, how might a cell raise the internal concentration to 2M without using a metabolic pathway?#2What might happen if a cell continually secreted enzymes, but never participated in endocytosis?