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Transcript
BIOLOGY 12 - Cell Membrane Notes TRANSPORT ACROSS THE MEMBRANE Please Label the Parts of the Cell Membrane THERE ARE TWO GENERAL MEANS BY WHICH SUBSTANCES CAN ENTER AND EXIT CELLS: I. Passive Transport II. Active Transport Requires no energy and follows the concentration gradient. Requires energy and goes against the concentration gradient. 1. DIFFUSION 2. OSMOSIS 3. FACILITATED TRANSPORT 1. ACTIVE TRANSPORT 2. ENDOCYTOSIS 3. EXOCYTOSIS Membrane and Transport Notes.doc Page 1 1. DIFFUSION BEFORE AFTER • Diffusion is a physical process that can be observed with any type of particle. • Law of Diffusion: molecules MOVE FROM AN AREA OF HIGH CONCENTRATION TO AN AREA OF LOW CONCENTRATION UNTIL EQUALLY DISTRIBUTED. • movement of molecules by diffusion requires no energy to be added (although adding energy (i.e. heat) will speed it up). • is a slow process - diffusion in liquid is slower than in gas Three Ways of increasing the rate of diffusion: 1. increase the temperature Membrane and Transport Notes.doc Page 2 2. increase the concentration gradient 3. decrease the size of the diffusing molecules • properties of the cell membrane allow few types of molecules to pass by diffusion: Lipid-soluble molecules like steroids and alcohols can diffuse directly across because the membrane itself is made of lipids 2. Osmosis • is the movement of water from an area of high water conc. to an area of low water conc. across a selectively permeable membrane • Water diffuses readily across membrane, through charged, protein-lined pores in the membrane (remember, water is not lipid-soluble) that will not allow anything else but water through. Solute: particles which are dissolved in water. Solvent: liquid which dissolves the solute. This is water when we are talking about osmosis. Solution: combination of solute and solvent. Membrane and Transport Notes.doc Page 3 Osmotic Pressure: the pressure due to the flow of water from the area of greater concentration to the area of lesser concentration. The greater the concentrations difference across the membrane, the greater the osmotic pressure. Membrane and Transport Notes.doc Page 4 Summary of what happens to ANIMAL CELLS placed in different tonicities of solution: Tonicity of Solution Cell is Put Into Net Movement of Water Effect on Cell Isotonic No net movement Remains the same Hypotonic Cell gains water Cell Swells & May Burst H2O “lyses” Hypertonic Cell loses water Cell Shrinks H2O “crenates” (animals) “plasmolysis” (plants) Membrane and Transport Notes.doc Page 5 3. FACILITATED TRANSPORT • Utilizes PROTEIN CHANNELS in cell membrane to control passage of molecules in and out of cell. • are highly specific - each carrier passes only one type molecule • Molecules only pass along concentration gradient. • REQUIRES NO ENERGY - is like diffusion in this sense • Explains how lipid-insoluble molecules like GLUCOSE and AMINO ACIDS cross the cell membrane. FACILITATED TRANSPORT BEFORE OUTSIDE CELL INSIDE CELL OUTSIDE CELL Membrane and Transport Notes.doc INSIDE CELL Page 6 II ACTIVE TRANSPORT: Active Transport: • performed by protein carriers • REQUIRES ENERGY (ATP) • moves molecules against the conc. gradient (moving from an area of low conc. to an area of high conc). ACTIVE TRANSPORT BEFORE OUTSIDE CELL INSIDE CELL OUTSIDE CELL INSIDE CELL Membrane and Transport Notes.doc Page 7 ENDOCYTOSIS AND EXOCYTOSIS • are both forms of Active Transport and require ATP energy - energy required because they are changing the shape of the cell membrane. It requires a great deal of energy to fuse a vacuole with the cell membrane or create a vacuole from the cell membrane. The vacuoles are made from a phospholipid bilayer that is the same as the cell membrane’s bilayer. This is why they can fuse together. • ENDOCYTOSIS: cell membrane forms a vesicle around the substance to be taken in. • Phagocytosis: what you call endocytosis if particles taken in are really large (like other cells e.g. human macrophages). Can be seen with light microscope. • Pinocytosis: (= cell drinking) - same idea as phagocytosis, except smaller particles taken in (requires electron microscope to see). Membrane and Transport Notes.doc Page 8 • EXOCYTOSIS: Reverse of endocytosis. Vacuole within cell fuses with cell membrane and the vacuole contents are deposited on the outside. Important in secretion and excretion in cells. Membrane and Transport Notes.doc Page 9