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Plasma Membrane Two key components of the membrane: phospholipids proteins The plasma membrane is semi-permeable (selectively permeable) It controls what goes into and out of the cell Two forms of transport: Passive Transport Active Transport • No energy needed • ENERGY used • WITH the gradient (high to low) • AGAINST the gradient • Examples: • Examples: – Diffusion – Osmosis – Endocytosis – Exocytosis Phospholipids • The phospholipids line up to form a double membrane • Small, uncharged particles are able to pass right between the phospholipids • This is called simple diffusion Proteins • There are also proteins embedded between the phospholipids. • These proteins function as gates, allowing larger or charged molecules to get in/out of the cell • Only molecules which are “recognized” are allowed thru these proteins • This is facilitated diffusion Passive transport: Diffusion Higher Concentration Lower Concentration Molecules collide – pass thru membrane Passive Transport: Osmosis • The movement of water • Water moves TOWARDS the molecules • Think of it as “water wants to dissolve stuff” • Which way will water move in each case? Passive Transport: Osmosis ISOtonic HYPERtonic HYPOtonic The effect of osmosis on cells HYPERTONIC ISOTONIC HYPOTONIC Passive transport: osmosis Osmosis Which way will water move? Hypertonic or Hypotonic? Crossing the Plasma Membrane Active transport AGAINST the gradient requires energy Figure 3.8 Active Transport • Endocytosis – Pino– Phago- • Exocytosis Ion pumps: Thru a protein, but using energy Figure 3.9 Crossing the Plasma Membrane Passive Transport Active Transport Crossing the Plasma Membrane Passive Transport Active Transport • No energy needed • ENERGY used • WITH the gradient • AGAINST the gradient • Diffusion • Can be through a protein • Osmosis • Endocytosis • Exocytosis Post test • What is the job of the plasma membrane? • What is semi-permeable? • What is the difference between active transport and passive transport? • What is osmosis? • What will happen to a cell when placed in a hypertonic solution? Hypotonic solution?
