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HOMEOSTASIS AND THE CELL MEMBRANE HOMEOSTASIS – MAINTAINING CONSTANT INTERNAL CONDITIONS I. Transportation through the Cell Membrane— small molecules such as H2O, CO2 and O2 move easily through the lipid bilayer – larger molecules require different mechanism A. Passive transport – NO energy required 1. Diffusion -- movement of particles from a high concentration to a low concentration a. example: dye (ex: food coloring) in water dye diffuses down concentration gradient until equilibrium reached concentration gradient = difference in concentration of a substance b. example: blood vessel in lung tissue during respiration blood X X X X X X CO2 high l lung l l O O l O O l O O l blood X O O X X O O2 high c. example: sugar dissolved in water solution – sugar water solvent – water (dissolving substance) solute – sugar (substance being dissolved) l l l l l l lung X O O X X O solute (sugar cube) solution solvent (H2O) 2. Osmosis -- diffusion of water through a selectively permeable membrane permeable to H2O impermeable to salt Water Salt salt water tap water Hypotonic = Low Salt Concentration High Water Concentration High Salt Concentration Low Water Concentration = Hypertonic a. hypertonic solution – high in solutes, low in solvent hypotonic solution – low in solutes, high in solvent isotonic solution – equilibrium has been reached Ex: cell in salt water water moves into cell water moves in and out of cell water moves out of cell cytolysis plasmolysis Red Blood Cell SALT SUCKS!! Plant cell b. example problem: A cell that is 80% H2O and 20% other is put into water that is 99% H2O and 1% other. Which way will the water move? Into cell 99% H2O Which is the hypotonic solution? Outside cell 1% other Which is the hypertonic solution? Inside cell c. cell bursts – cytolysis cell shrinks – plasmolysis (lysis = splitting) 80% H2O 20% other 3. Facilitated diffusion-- Most molecules move across the membrane with help from protein channels - provides a larger opening for organic molecules to go through a. example: glucose (food molecules) Glucose molecules (high concentration) outside of cell protein protein pump channel --------------------------------------------------------------NO ENERGY REQUIRED------------------------------------------------------------------inside of cell -----------------------------------------------------------------ENERGY REQUIRED-------------------------------------------------------------------B. Active transport – energy required in form of ATP 1. Some proteins act like pumps moving molecules from LOW to HIGH concentration. a. example: vitamins and minerals in soil concentrated into plants = calcium ion Outside cell Inside cell b. example: Body cells must pump CO2 out into the surrounding blood vessels to be carried to the lungs to exhale. Blood vessels are high in CO2 compared to the cells, so energy is required to move the CO2 across the cell membrane from LOW to HIGH concentration. outside of cell inside of cell Carbon dioxide molecules Protein pump 2. Endocytosis/ Exocytosis – how very large molecules (food and waste) get into and out of cell a. Endocytosis – into cell 1. Phagocytosis – solids example: white blood cell engulfing bacteria to destroy it (immune reaction) 2. Pinocytosis – liquids example: water into cell b. Exocytosis – out of cell example: cellular waste II. Flow Chart A. Homeostasis – maintaining constant internal conditions B. Cell membrane constantly working on maintaining homeostasis within the cell NO ENERGY NEEDED: high to low conc. Passive Transport Diffusion Osmosis Facilitated Diffusion (protein channels) ENERGY NEEDED: low to high conc. Active Transport Endocytosis (phagocytosis and pinocytosis) Exocytosis