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Transcript
Chapter 7 III. Cell Boundaries • All cells have a _____________________________and some have a cell wall Cell membrane Interest Grabber Section 7-3 • How is a window screen similar to a cell membrane? Read on to find 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? Go to Section: A. Cell Membrane • Regulates what enters and leaves the cell and also provides _____________________________. • Almost all cell membranes are made of a double layered sheet called a ___________________________-flexible,yet strong barrier • Cell membranes usually have a protein molecule imbedded in the bilayer w/ carbohydrate molecules attached • Called a _________________model • Some of the proteins form channels or pumps to move material across the membranes • Some of the carbs act as ____________________tags Protection and support Phospholipid bilayer Fluid mosaic Chemical id tags Figure 7-15 The Structure of the Cell Membrane Section 7-3 Outside of cell Proteins Carbohydrate chains Cell membrane Inside of cell (cytoplasm) Go to Section: Protein channel Lipid bilayer B. Cell Walls • In plants,algae,fungi, and many prokaryotes • Lie _______________the cell membrane • Usually porous enough to let water,O2,CO2 and certain other substances to pass through easily • Main function is support and protection • Usually made of fibers of ____________________produced in cell and secreted to surface • Mostly _____________________-tough carb fibers Carbohydrate and protein outside cellulose C.Diffusion Through Cell Boundaries • Every cell is in a liquid environment • Cell membrane regulates the movement of cell materials from one side to the other 1.Measuring concentration – • Cytoplasm is a solution of various substances in water _____________of a solution is the mass of solute in given volume of solution---ie. Mass/volume…..If you have 15 g salt in 3 mL water,what is the concentration?------_______….If you have 24 g salt in 2mL water you would have 12 g/mL salt….Which solution is more concentrated?______________ 12 g/mL 5g/mL concentration 2. Diffusion – • In a solution the particles move constantly,spreading out randomly….tending to move where more concentrated to an area less concentrated…This is called __________________. – ____________________= concentration of a solute is the same throughout a system – does not require energy because random movement if equilibrium is reached,particles keep moving across the membrane,still balancing concentration isotonic D. Osmosis Figure 7-17 Osmosis Section 7-3 Higher Concentration of Water Water molecules Cell membrane Lower Concentration of Water Sugar molecules Go to Section: D. Osmosis – Some molecules are too large or too strongly charged to make it across the lipid bilayer----thus impermeable to it – Most membranes are selectively permeable – _____________________is the diffusion of water across a selectively permeable membrane – water moves easily and will move to balance the concentration of a solute,water moving from area of higher to lesser conc. For the WATER – ____________________-same strength of a solute on both sides of a cell membrane osmosis isotonic – more concentrated side of solute is ____________________ – less concentrated side is____________________ – Osmosis exerts a pressure known as ____________________________on the hypertonic side of a membrane….This could results in a cell bursting – Bursting not so much a problem in larger organisms….tend to be in isotonic environments • Osmotic pressure may not allow a plant or bacterial cell to burst , but could weaken the cell wall hypertonic hypotonic Osmotic pressure E.Facilitated Diffusion » » » Protein channels Some molecules,like glucose ,diffuse quickly across due to ________________________ These allow only certain molecules to pass Since it is diffusion it does not require energy and still goes from area of higher to lower concentration F.Active Transport--– ____________________________________________ ___________________________________ – Requires much energy – Usually carried out by proteins or pumps found in the membrane Moves materials across a concentration gradient,or difference 1. Molecular Transport – Small molecules and ions carried by proteins that act like energy requiring pumps • Ca ,K,and Na ions are carried Endocytosis and Exocytosis • • • Transports larger molecules and even clumps of matter ________________________is the process of taking material inward by enfolding,or pockets In endocytosis ,the pocket breaks loose from the cell membrane and forms a vacuole…large molecules,food and even whole cells can be taken in this way endocytosis 2 examples of endocytosis are – ___________________-extensions of cytoplasm surround a particle and package it in a food vacuole,then the cell engulfs it ---This is how amoebas eat-----is a form of active transport • _______________-Cells use this to take up liquids in the environment—tiny pockets filled w/ liquid form along the cell membrane and pinch off to form vacuoles phagocytosis pinocytosis – ___________________________--releases large amounts from the cell by pinching off or a contractile vacuole as in paramecium--also active transport exocytosis Figure7-20 Active Transport Section 7-3 Molecule to be carried Low Concentration Cell Membrane High Concentration Molecule being carried Low Concentration Cell Membrane High Concentration Energy Go to Section: Energy