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Transcript
In or Out? 1. What are some things that can pass through a window screen? 2. What are some things that cannot pass through a window screen? Why is it important to keep these things from moving through the screen? 3. The cell is surrounded by a cell membrane, which regulates what enters and leaves the cell. Why is it important to regulate what moves into and out of a cell? Sec 7-3: Cell Boundaries Two Types of Cell Boundaries 1. Cell wall (outer) Strong supporting layer outside cell membrane Only in some organisms -plants, algae, fungi, prokaryotes Porous 2. Cell membrane (inner) Thin, flexible layer that surrounds all cells Plant Cell: Has Cell Wall and Cell Membrane (Cell) Functions of Cell Membrane 1. Regulates what goes in and what comes out of a cell 2. Protects cell 3. Supports cell, but also flexible Outside Section 7-3 of cell Figure 7-12 The Structure of the Cell Membrane Structure of Cell Membrane Carbohydrate chains Proteins Cell membrane Inside of cell (cytoplasm) Protein channel Lipid bilayer Main Parts of Cell Membrane Section 7-3 • 1. Phospholipid bilayer – 2 layers Phospholipid – Phosphate “head” = is polar = likes water – Lipid “tails” = are non-polar = do not like water (is why phospholipids align a certain way) Phosphate head: is in water Lipid tails: point away from water Phosphate head: is in water • 2. Proteins – Embedded in lipid bilayer – Form channels and pumps • 3. Carbohydrates – Allow individual cells to identify one another • 4. Cholesterol – Regulates membrane fluidity over wide range of temperatures • Warm temp. = Prevents membrane from becoming too fluid • Cold temp. = Prevents membrane from becoming frozen Membrane = Fluid Mosaic Model Why? Fluid = is flexible and moveable Mosaic = made of so many kinds of molecules Like mosaic artwork made of so many different tiles Terms to Know • A solution is a mixture of two or more substances, evenly mixed – Solutes = substances dissolved in the solution • The cytoplasm is a solution of many different substances • Concentration = mass of solute in a given volume of solution – Mass/volume Passive Transport [High] to [Low] Does not require energy!!!!! • DIFFUSION • FACILITATED DIFFUSION • OSMOSIS DIFFUSION: Definition High Concentration MOVE from an AREA OF HIGH CONCENTRATION to an AREA of LOW CONCENTRATION Low Concentration Diffusion • Def. of permeable = membrane that lets substances pass through it • Cell membrane is selectively permeable, which means that it lets some things in but does not let other things in • Substances keep moving till there is about equal amounts of them on both sides of the membrane = at equilibrium Factors that Affect Diffusion • Amounts of substances involved • Temperature • Pressure • Stirring -speeds up the rate of diffusion OSMOSIS • Deals with movement of water – From greater to lesser area of water • Particles can’t move because membrane won’t allow it! Types of Solutions (refers to solution outside of cell) • Hypotonic (“hypo” = less) – Less solutes outside cell = more water – More solutes inside cell = less water Water rushes into cell (cell swells up like a hippo = hypo) • Hypertonic (“hyper” = more) – More solutes outside cell = less water – Less solutes inside cell = more water Water leaves cell • Isotonic (“iso” = same) – Same amount of solutes inside and outside cell Water stays where it is Types of Solutions Examples Osmotic Pressure • Pressure exerted on hypertonic side of a selectively permeable membrane – Cell walls prevent the cell from expanding • Some organisms fight osmotic pressure by using a contractile vacuole – pumps excess water out of the cell – Ex. paramecium Facilitated Diffusion • Passive – Proteins used in facilitated diffusion are called channels – Channels are specific to certain molecules – 100 different protein channels RECAP • What are 3 major types of passive transport? • What characterizes these as passive? • Describe how the concentration of molecules moves within this type of transport. • What would happen to a red blood cell placed in a hypertonic solution? Active Transport • ENERGY NEEDED! Molecule to be carried • Molecules go from lesser to greater concentration “against concentration gradient” • Also used for when LARGE molecules need to get through membrane • May or may not need channel proteins – called pumps Energy Molecule being carried Endocytosis and Exocytosis • Endocytosis = process by which cells take in large molecules from the outside -eg.: pinocytosis – large amounts of liquid phagocytosis – large amounts of solid • Exocytosis = process by which cells get rid of large molecules in the cell; leaves cell. • Vacuole fuses with membrane to dispel Pinocytosis Pinocytes are pockets on the cell membrane. Subtances are engulfed and a vacuole forms around them Phagocytosis: Engulfing • This is when large molecules are surrounded and pulled into the cell • Examples: amoeba, white blood cells called phagocytes • This is the same method used by white blood cells to trap bacteria in our blood Types of Transport ACTIVE requires Energy Exocystosis & Endocytosis PASSIVE Does not need energy Diffusion Osmosis Facilitated Diffusion RECAP What are some examples of active transport? Describe the concentration gradient involved in active transport How is active transport different from passive transport? Exit Questions When is equilibrium reached? What is the difference between osmosis and diffusion? What is the difference between active and passive transport?