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YOUTUBE Membrane Rap Membrane Rap The Cell Membrane - Why do cells need membranes? What functions does it perform? 1. Keep the overall structure of a cell. Keeps things in the cell (ex. Cytosol, organelles). Keeps things out (ex. Toxins, excess water). Movement. 2. 3. 4. What kind of things move across this membrane? Some examples: Sugars Charged ions (+/-) H2O O2 CO2 What are some ways molecules move across the cell membrane? Passive Transport! 1. Simple Diffusion 2. Facilitated Diffusion 3. Osmosis ENDOcytosis and EXOcytosis! 1. Phagocytosis 2. Pinocytosis 3. Receptor Mediated Endocytosis Require no chemical energy!!! 1. Simple Diffusion Unassisted diffusion! The solutes transported with way are either (in order to pass through our LIPID bilayer) or are enough to pass through the membrane pores. 2. Facilitated Diffusion The transporting of substances across the cell membrane from an area of to an area of by means of a carrier molecule. In the cell membrane these are ! 3. Osmosis Osmosis is the diffusion of water molecules. Water molecules diffuse across a semi permeable membrane (the cell membrane) from a region of concentration to an area of concentration. Endocytosis Endocytosis is a process in which single-celled organisms take in substances such as large polar molecules that cannot cross the hydrophobic plasma membrane. In endocytosis the cell ingests substances by and surrounding the food particle. 1. Phagocytosis The material taken in by the cell is a such as bacterium or a fragment of organic matter. 2. Pinocytosis If the material taken in by the cell is is known as pinocytosis. the process 3. Receptor Mediated Endocytosis This applies to specific molecules (ex. Low Density Lipoproteins). Molecules to be transported first bind to on the plasma membrane (receptor proteins). The interior portion of the receptor protein is embedded in the membrane. The protein clathrin coats the inside of the membrane in the area of the pit. When an appropriate collection of molecules gather in the coated pit, the pit deepens and seals off to form a coated vesicle which carries the molecule into the cell. Exocytosis JUST THE REVERSE!! Exocytosis is the reverse of endocytosis. This process results in the discharge of material from vesicles at the cell surface to the outside of the cell.