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Transcript
Diffusion and Osmosis Warm Up DEFINE DIFFUSION Outline • Learn the concepts of: – Diffusion, osmosis, semipermeable membrane, isotonic, hypertonic, & hypotonic • Plant/animal cells exposure to water – Hypertonic Env. – Hypotonic Env. – Isotonic Env. Diffusion • Solute molecules moving from an area of high concentration to an area of low concentration (water) – Random motion drives diffusion – Movement is based on kinetic energy (speed), charge, and mass of molecules – Equilibrium is reached when there is an even distribution of solute molecules 1 2 3 4 Osmosis • Movement of water through a semi-permeable membrane – Semi-permeable: permeable to solvents (WATER), but not to large molecules – High [water] to low [water] • Dissolved molecules (i.e. glucose, starch) are called solutes • REMEMBER: Water = solvent Glucose, Starch = solutes Effect of Water on Cells • Hypertonic Environment – High [solute], low [water] • Hypotonic Environment – High [water], low [solute] Hypertonic Hypotonic Isotonic • Isotonic Environment – [water] = [solute] Osmosis in Living Cells Cellulose in cell wall Osmosis in Red Blood Cells Isotonic Crenation Hypertonic Hypotonic Effect of Water on RBC Diffusion and Osmosis Warm Up DEFINE OSMOSIS INTRO • Organisms are constantly responding to their environment. • Homeostasis = ability of an organism to maintain a constant internal condition despite external environmental changes. INTRO – Cell Membrane is selectively permeable to different substances – Some substances use energy to transport across a membrane, while others don’t need energy to move across cell. Passive Transport • Movement across the cell membrane that does NOT REQUIRE ENERGY from the cell. • Concentration Gradient = A difference in the concentration of a substance across a space Passive Transport • Equilibrium = A condition in which the concentration of a substance is equal throughout a space. • Diffusion = The movement of a substance from an area of high concentration to an area of low concentration caused by the random motion of particles of the substance. Passive Transport • If diffusion is allowed to continue, equilibrium results! • The non-polar interior of the cell membrane’s lipid bilayer repels ions and polar molecules and prevents substances from diffusing across the cell membrane. • Small or non-polar molecules can diffuse across the cell membrane down their concentration gradient. Water Diffuses Into & Out of Cells By Osmosis • Osmosis = The diffusion of water through a selectively permeable membrane. • Involves the movement of water down its concentration gradient. • Type of passive transport! Water Diffuses Into & Out of Cells By Osmosis • The direction of the water movement across the cell membrane depends on the concentration of free water molecules in the cytoplasm and in the fluid outside of the cell. 3 Possibilities for Direction of Water Movement 1. H2O MOVES OUT – cell shrinks! HYPERTONIC SOLUTION 2. H2O MOVES IN – cell swells! HYPOTONIC SOLUTION 3. NO H2O MOVEMENT – cell remains same size ISOTONIC SOLUTION 3 Possibilities for Direction of Water Movement If swelling is left unchecked, cell could BURST! How do cells deal with this? • Plant cells – rigid cell walls and contractile vacuoles • Animal cells – remove dissolved particles from cytoplasm – Increases free H2O molecules inside of cell • Example: Common remedy for a sore throat is to gargle with salt water. WHY? Proteins Help Some Substances Cross the Cell Membrane • Transport Proteins – CHANNELS – provide polar passageways through which substances can move across the cell membrane. • Selective! – only specific substances are allowed to pass! (sugars, amino acids) Facilitated Diffusion • Carrier Proteins = Transport protein that carries a specific substance across a cell membrane. • Facilated Diffusion = When carrier proteins are used to transport specific substances (amino acids/sugars) DOWN their concentration gradient. Facilitative Diffusion • http://highered.mcgrawhill.com/olc/dl/120068/bio02.swf Diffusion and Osmosis Day 3 Notes Warm Up What is the difference between active and passive transport? 4:2 Active Transport • Some substances are transported against the concentration gradient. Active Transport • Active transport = Transport of a substance across a cell membrane against its concentration gradient. • Requires the cell to use energy – supplied by ATP Vesicles Move Substances Across Membranes • Endocytosis = The movement of a substance into a cell by a vecisle • Exocytosis = The movement of a substance by a vesicle to the outside of the cell • Endocytosis • Exocytosis