Transcript Slide 1
Passive Transport Where are membranes found? • Cell • Organelles Cell Membrane a.k.a. semipermeable • Allows certain things to enter and leave • Phosphate head • Lipid tail • Two layers phospholipid bilayer Concentration – amount of substance in a given volume High Concentration Low Concentration Passive Transport Passive • Movement of materials that DOES NOT require energy (ATP) Passive Transport Passive Diffusion High Concentration Low Concentration Diffusion • Move from HIGH to LOW concentration – “passive transport” – no energy needed diffusion movement of water osmosis Diffusion across cell membrane • Cell membrane is the boundary between inside & outside… – separates cell from its environment OUT: waste IN: food carbohydrates sugars, proteins amino acids lipids salts, O2, H2O OUT IN ammonia salts CO2 H2O products Diffusion • Continues until an equilibrium is reached – Equilibrium – balanced; equally distributed • What will happen when dye is added to a beaker of water? a b c What causes diffusion? • Movement of molecules – As they move they bump into each other • Collisions cause molecules to move away from each other – http://www.stolaf.edu/people/giannini/flasha nimat/transport/diffusion.swf Factors Affecting Diffusion • Temperature—the higher the temperature, the faster diffusion occurs • Molecular Size—the bigger the molecule, the longer diffusion takes Passive Transport Passive Diffusion Osmosis Osmosis • Diffusion of water across a selectively permeable membrane. • Occurs until concentration is balanced on both sides of the membrane. Osmosis is diffusion of water • Direction of osmosis is determined by comparing total solute concentrations – Hypertonic - more solute, less water – Hypotonic - less solute, more water – Isotonic - equal solute, equal water Hypertonic • Medium has more solute than the cell • More water leaves the cell than enters it • Cell will shrink Hypotonic • The medium has less solute than the cell • More water enters the cell • The cell will swell Isotonic • Medium is exactly the same solute concentration as the cell • Amount of water moving in equals water going out • The cell will stay the same size What is happening here? Passive Transport Passive Diffusion Osmosis Facilitated Diffusion Isnt the membrane “semi-permeable”? • What molecules can get through directly? – fats & other lipids What molecules can lipid inside cell salt NH3 NOT get through directly? polar molecules H 2O ions salts, ammonia outside cell sugar aa H2O large molecules starches, proteins Channels through cell membrane • Membrane becomes semi-permeable with protein channels – specific channels allow specific material across cell membrane inside cell NH3 H2O salt aa sugar outside cell Facilitated Diffusion • Diffusion through protein channels – channels move specific molecules across cell membrane facilitated = with help – no energy needed open channel = fast transport high low “The Bouncer” Active Transport • Cells may need to move molecules against concentration gradient – shape change transports solute from one side of membrane to other – protein “pump” – “costs” energy = ATP low ATP high Active Transport ATP ATP How about large molecules? • Exocytosis – Through vesicles & vacuoles – “Exit Cell” Endocytosis • Endocytosis – phagocytosis = “cellular eating” – pinocytosis = “cellular drinking Review ? Review Getting through cell membrane • Passive Transport – Simple diffusion • diffusion of nonpolar, hydrophobic molecules – lipids – high low concentration gradient – Facilitated diffusion • diffusion of polar, hydrophilic molecules • through a protein channel – high low concentration gradient • Active transport – diffusion against concentration gradient • low high – uses a protein pump – requires ATP ATP Transport summary simple diffusion facilitated diffusion active transport ATP Any Questions??