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Cell Structure & Function Structure & Movement Through Membranes (There and Back Again) Foothill High School Science Department The Cell Membrane Key Concept: The cell membrane regulates what enters and leaves the cell and also provides protection and support Foothill High School Science Department The Cell Membrane • The cell takes in nutrients and expels wastes plus cell products through the cell membrane • The Basic Structure Of Nearly All Cell Membranes Is The LIPID BILAYER Foothill High School Science Department LIPID BILAYERS • Form Automatically When Certain Lipids Are Dissolved In Water • Tough Flexible Structure • Strong Barrier Between Cell Contents And Its Surroundings Foothill High School Science Department LIPID BILAYERS Foothill High School Science Department LIPID BILAYERS Foothill High School Science Department Fluid Mosaic Model In Addition To The Bilayer, The Cell Membrane Contains: • Proteins That Form – Channels & Pumps • Proteins with Carbohydrates That Form – Antigenic Sites – Communication Sites Foothill High School Science Department Foothill High School Science Department Diffusion All Living Cells Contain And Are Surrounded By Liquid. • THE CELL MEMBRANE REGULATES THE MOVEMENT OF MOLECULES FROM ONE SIDE OF THE MEMBRANE TO THE OTHER Foothill High School Science Department Cytoplasm Is A Solution Of Many Different Substances In Water Foothill High School Science Department Solution A liquid mixture of 2 or more substances evenly mixed. • Solvent – The liquid in which the substances are mixed • Solute – Substances dissolved in the Solvent Foothill High School Science Department Concentration Of Solution Concentration = Mass of the solute in a given volume of solvent. Mass/Volume e.g. 12g of NaCl dissolved in 3L H2O equals 12g/3L or 4.0 g/L Foothill High School Science Department In A Solution Molecules Are Moving Constantly They Collide and Bounce off each other This causes them to spread out randomly Resulting In: Movement from: an area of higher concentration to an area of lower concentration This process is called: Diffusion Foothill High School Science Department DIFFUSION • Molecules move away from an area of Higher Concentration to area’s of Lower Concentration • Equilibrium – Concentration of a solute is the same throughout the solution • The concentration is the same EVERYWHERE Foothill High School Science Department Diffusion Foothill High School Science Department DIFFUSION Key Concept: Diffusion Causes Many Substances To Move Across A Cell Membrane But: Diffusion Does NOT Require The Cell To Use Energy It just happens naturally! Foothill High School Science Department Diffusion & Cells • Substances that can diffuse across cell membranes will do so until equilibrium is reached Diffusion continues after equilibrium but the rates are equal in ALL Directions Atoms & Molecules Never Stop Moving Foothill High School Science Department OSMOSIS Foothill High School Science Department Osmosis Requires A Membrane • Permeable Membrane – Substance Can Easily Cross • Impermeable Membrane – Substance Can NOT Cross • Selectively Permeable Membrane aka = Semipermeable Membrane – Some Substances Can Cross, Others Can Not – Cell Membranes are Semipermeable Foothill High School Science Department OSMOSIS Key Concept: Osmosis = The Diffusion Of Water Through A Selectively Permeable Membrane Foothill High School Science Department Foothill High School Science Department The Tonics • Hypotonic – Less concentrated solution • Isotonic – Equally concentrated solution • Hypertonic – More Highly concentrated solution Foothill High School Science Department The Tonics Foothill High School Science Department The Tonics Foothill High School Science Department How Osmosis Works • Overhead – Sugar & Water • Membrane Impermeable To Sugar • Water moves from a higher concentration of WATER to a lower concentration of WATER (NOT Sugar) Foothill High School Science Department Osmotic Pressure • Pressure exerted on the hypertonic side of a selectively permeable membrane • May cause cells to shrink or burst Foothill High School Science Department Osmotic Pressure Cell Membrane Contractile Vacuoles Foothill High School Science Department Facilitated Diffusion • Molecules that can easily diffuse across the cell membrane: –Alcohol –Water –Small Lipids Foothill High School Science Department Facilitated Diffusion • Other molecules can not pass through the cell membrane but still get into the cell. HOW? Foothill High School Science Department Facilitated Diffusion • Thru Protein Channels in the Cell Membrane that allow a substance to cross. –Allows Diffusion In Both Directions –Each Channel Substance Specific –DOES NOT REQUIRE ENERGY Foothill High School Science Department Facilitated Diffusion Protein Channel Is Substrate Specific Substrate Can Move Either Direction Depending On Concentration. Always from area of Higher Concentration to area of Lower Concentration! Foothill High School Science Department Active Transport • Moves Material Across A Cell Membrane • Against A Concentration Gradient (from area of Lower concentration into an area of Higher concentration) Foothill High School Science Department Active Transport Requires Energy Foothill High School Science Department Energy Molecule Foothill High School Science Department Active Transport Foothill High School Science Department Active Transport • Endocytosis – Used to bring in large molecules, food, and whole cells • Exocytosis – Membrane surrounded material from inside the cell fuses with the cell membrane, releasing the contents. Foothill High School Science Department Foothill High School Science Department