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Transcript
CELL MEMEBRANE STRUCTURE AND FUNCTION The cell membrane is a double layer of phospholipids molecules with protein molecules sticking through it. Some of these proteins act as proteins channels to help move substances into and out of the cell. QuickTime™ and a decompressor are needed to see this picture. Each phospholipid molecule has a polar (LOVES water) head and 2 non-polar (HATES water) tails. For all cells, the plasma (cell) membrane forms a boundary between the living cell and its surroundings and controls the traffic of molecules into and out of the cell. It allows some substances to cross more easily and blocks passage of some substances completely; for this reason we call the plasma (cell) membrane) semi-permeable or selectively permeable. They are arranged like this: (Loves water) QuickTime™ and a decompressor are needed to see this picture. Tails (Hates water) Heads A soap bubble has a similar design, so soap bubbles can be used to understand some of the properties of the cell membrane…YEAH!!! MATERIALS: Square plastic plate to hold bubble solution Square template of straws and string – the cell membrane Toothpick Circular hair tie Paperclip Clear tubing – protein channel PROCEDURE: MAKING THE CELL MEMBRANE • Your teacher will fill your plate with half an inch of soap solution. • Holding onto the straw handles of your cell membrane template, dunk the template into the soap solution. • Raise your template out of the pan and allow the excess soap to drop off. • Hold your “bubble” membrane up to show the following things a membrane can do. *WRITE ALL ANSWERS IN YOUR COMPOSITION BOOK. USE COMPLETE SENTENCES. NUMBER YOUR ANSWERS* PART A: FLUIDITY DEFINE: Selectively permeable Fluid Mosaic Phospholipids Hydrophobic hydrophilic The “Fluid Mosaic Model” of the cell membrane means that the cell membrane is made up of many small molecules. Each one is moving around and changing position constantly. TO SHOW THIS: Let the lights shine off the bubble surface. Look at the movement you see within the bubble. A1. What are these soapy molecules doing? ________________________________________________________ PART B: FLEXIBILITY Within the membrane, molecules can move freely around and reorganize themselves into almost any sort of shape. TO SHOW THIS: • Make a new cell membrane • Twist your cell template in opposite directions into different shapes. B1. What happens to the soapy film? ______________________________________ PART C: SELF-SEALING DEFINE: Exocytosis Endocytosis Two Types of Endocytosis: Phagocytosis Pinocytosis • The CELL membrane is NOT solid. Some small molecules can pass through it. • Make a new cell membrane • Take a paper clip and pass it through the cell membrane. C1. What happens? ___________________________________________ Make a new cell membrane using your template. This time, dip the paperclip into the soapy solution first! Pass the paper clip through the soapy membrane to the other side. C2. Did the membrane seal around the object? _________________________________ C3. Why do you think the paper clip must be coated with soap in order to pass through the membrane? Relate the concept of semi-permeable (selectively permeable) to your results. Place the circular hair tie onto the surface of the bubble cell membrane. With your finger, pop the bubble surface inside the hair tie. Gently pull the hair tie to one edge of the cell membrane, until you pull the hair tie off the surface of the cell membrane. C4. Does the bubble seal as you pull the hair tie off of the surface? Why? Explain using the Concepts of exocytosis and endocytosis. Draw an example of the process. PART D: TRANSPORT PROTEINS DEFINE: Protein channel Facilitated diffusion Active transport Passive transport Small molecules, like water, can sometimes move into the cell through small holes in the cell membrane. Larger molecules cannot do this. They need to go through channels made by protein molecules in the membrane. TO SHOW THIS: • Take a small piece of rubber tubing • Make a new cell membrane • Carefully stick the rubber tubing halfway through the soapy membrane …CONGRATULATIONS, You made a model of a transport protein in a cell membrane Pass a toothpick through the “protein channel.” D1. What type of cell transport does this represent? Explain.