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Transcript
Biology Journal 12/12/2013 What does “concentration” mean? How can we use it to describe something? 2.4 Membranes Assessment statement 2.4.1 Draw and label a diagram to show the structure of membranes. The diagram should show: phospholipid bilayer, cholesterol, glycoproteins, integral proteins,, (embedded in the phospholipid of the membrane), peripheral proteins (attached to the plasma membrane surface), Use the term plasma membrane for the membrane surrounding the cytoplasm. 2.4.2 Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of cell membranes. 2.4.3 List the functions of membrane proteins: hormone binding sites, immobilized enzymes, cell adhesion, cell-to-cell communication, channels for passive transport, pumps for active transport 2.4.4 Define diffusion and osmosis. 2.4.5 Explain passive transport across membranes by simple diffusion and facilitated diffusion. 2.4.6 Explain the role of protein pumps and ATP in active transport across membranes. 2.4.7 Explain how vesicles are used to transport materials within a cell between the rough endoplasmic reticulum, Golgi apparatus and plasma membrane. 2.4.8 Describe how the fluidity of the membrane allows it to change shape, break and re-form during endocytosis and exocytosis. Cell Membranes and Cell Transport Diffusion is the passive net movement of molecules from a region of high concentration to a region of low concentration. Diffusion continues until equilibrium: when all of the concentrations are the same. Where is the high concentration? Where is the low concentration? Diffusion requires no energy from the cell (its passive). These molecules pass through the cell membrane automatically. Water is 55% to 75% of our body weight* *People that are more lean have more water than people who have more fat because muscle cells hold more water than fat cells. Osmosis is the diffusion of water Water diffuses so much in the bodies of living things that they give it a special name: osmosis. Diffusion happens across the cell membrane. You can cause osmosis to happen to cells by adding solutes that can’t diffuse across the cell membrane Leaf cells, before salt Leaf cells after adding salt In the Third Punic War (it took 3 tries) the Roman Army invaded the city of Carthage in 146 BC. They enslaved or killed everyone there and salted the Earth… Why salt the Earth? Why do your fingers get wrinkly in a bathtub? • Think about concentrations and osmosis… The cell membrane is made out of a special lipid called a phospholipid Phospholipids arrange themselves so that the hydrophobic parts are not touching water and the hydrophilic parts are touching water. The hydrophobic parts are not touching water and the hydrophilic parts are touching water. A solution consists of a solute dissolved into a solvent. What’s the solvent? What’s the solute? What’s the solution? Salt can pass through the membrane. Will it diffuse to the left or to the right? The solute (salt) moves from high concentration to low concentration Passive transport: diffusion, it is automatic (passive) Active transport: against diffusion, against the “concentration gradient,” requires energy Which type is in this picture? With or “down” the concentration gradient (facilitated diffusion) Against the concentration gradient At the end of 10 hour, when the bell rings, is that more like active or passive transport? Why? A 9 year old kid is told by her parents to put away all the toys into her toy box. Is that more like active or passive transport? Why? Exocytosis: Packaging up molecules in a vesicle and sending them outside the cell • Vesicles are made by the Golgi complex It’s kind of like taking out the garbage But, not everything released through exocytosis is garbage! Brain cells release dopamine from vesicles. This makes you feel happy when good things happen… Endocytosis: Taking in molecules from the outside and packaging them up in a vesicle. Phagocytosis is when a cell engulfs or “eats” another cell. A white blood cell engulfing some bacteria. Where might the bacteria be sent to once inside the cell?