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Membrane Transport: Passive & Active See 81-85 in your book See the handout What is the difference between passive and active transport? Passive Transport #1: Diffusion Passive Transport #2: Osmosis Passive Transport #3: Passive Transport #4: Ion Channels Active Transport #1: Membrane/Ion Pumps Active Transport #2: Endocytosis Active Transport #3: Exocytosis Key Definitions • Homeostasis: maintaining the internal conditions of the cell • Equilibrium: an equal amount of solutes on both sides of a membrane • Potential energy vs. Kinetic energy • Concentration gradient Passive Transport #1: Diffusion • Movement of molecules from area of [high] to [low] • Caused by kinetic energy; molecules simply colliding. • Ability to diffuse depends Size Polarity: like dissolves like Electric charge: opposites attract Passive Transport #1: Diffusion • Examples of diffusion: – CO2 and O2 are nonpolar. They can dissolve in lipids and diffuse across membrane – Small molecules can diffuse; what does this mean for large molecules like glucose?! Passive Transport #2: Osmosis • The diffusion of water • Solution = solute in a solvent • Water = “Universal Solvent” • Direction of osmosis – Shortcut: Water flows to area of higher solute concentration. Osmosis: Definitions of Solutions • Hypotonic: Solution with lower [solutes] • Hypertonic: Solution with high [solutes] • Isotonic: Solution with equal [solutes] • Pay attention to how a cell maintains equilibrium! (Pause to practice analyzing situations) How Do Cells Deal With Osmosis? • Isotonic? Vertebrates on land. Most sea organisms • Most freshwater organisms are in hypotonic environments (esp if unicellular) – Where is water constantly moving? – Contractile vacuoles: to pump water out (NOTE: This requires energy!) Multicellular organisms will get rid of solutes instead How Do Plants Deal With Osmosis? Generally, plants live in hypotonic environments. Turgor pressure: pressure that membrane exerts agains the cell wall as the cell fills with water. BUT Plants in hypertonic environments LOSE water Turgor pressure is…. Cell membrane …. This is PLASMOLYSIS (--> WILTING) See page 83 in your book How Do Animals Deal With Osmosis? Some cells cannot withstand changes caused by osmosis. (No cell walls, no contractile vacuoles, no solute pumps*) In hyptertonic solutions, what happens? In hypotonic solutions, what happens? CYTOLYSIS See page 83 in your book (Red blood cells) Passive Transport #3: • If molecules are large or not lipid soluble • Carrier proteins change shape, shield the molecule from nonpolar region of membrane – Specific to each molecule: glucose; each amino acid Passive Transport #4: Ion Channels • Ions like K+, Na+, Ca2+, Cl- are not lipid soluble • Specific to each ion: Basic Ion Channel • Some are “gated” – Membrane stretching – Electrical signals – Chemical signals Check out this potassium channel Active Transport: What’s so special about active transport? • Solute moves from [LOW] to [HIGH] • Like going uphill, or upstream, this requires energy – “Up the concentration gradient” (Keep in mind the osmosis issues that require active transport) Active Transport #1: Membrane Pumps a.k.a. Na-K Pump Acts like a carrier protein BUT ATP is needed to fuel the activity Animal cells need Na outside and K inside The ATP changes the shape of the protein… Basic Ion Pump How The Pump Works *Important for creating gradients leading to membrane potential aka voltages Active Transport #2: Endocytosis • To transport things INTO the cell. • Phagocytosis: transport large particles or whole cells, bacteria and viruses (Cell eating) • Pinocytosis: transport solutes or fluids (cell drinking) • Membrane folds in and forms a vesicle • Some vesicles fuse with lysosomes, which digest the contents. Paramecium! Neutrophils! Macrophages! Active Transport #3: Exocytosis • Reverse of endocytosis • To release large molecules made by the cell… – Proteins can be made by the ribosomes on rough ER, then packaged into vesicles by Golgi apparatus, and secreted – Endocrine system is a good example – To get rid of waste Paramecium Performing Exocytosis Membrane Transport Passive Transport #1: Diffusion Passive Transport #2: Osmosis Passive Transport #3: Passive Transport #4: Ion Channels Active Transport #1: Membrane/Ion Pumps Active Transport #2: Endocytosis Active Transport #3: Exocytosis