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Pretest • 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? • What are examples of each? The plasma membrane maintains homeostasis for the cell It is selectively permeable: It controls what goes into and out of the cell Two forms of transport across the membrane: Passive Transport Active Transport No energy needed • ENERGY used • WITH the gradient (high to low) • AGAINST the gradient • Examples: • Examples: – Diffusion – Osmosis – Endocytosis – Exocytosis Plasma Membrane Structure Two key components of the membrane: phospholipids proteins Crossing the Plasma Membrane: Passive Transport Energy? Direction? Examples? Passive Transport: Diffusion • 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 Passive Transport: Diffusion • 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 Concentration gradient: 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 HYPERtonic ISOtonic HYPOtonic The effect of osmosis on animal cells Cytolysis What do plant cells have outside of the cell membrane that animal cells do not have? What difference will this make with osmosis? Effect of osmosis on plant cells Flaccid - Turgid due to plasmolysis - cell shrinks from cell wall Passive transport: osmosis Osmosis Which way will water move? Hypertonic or Hypotonic? Active Transport: Which direction? Energy Used? Examples? 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? • What are examples of each?
