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Explore the cell boundaries, from membranes to walls, regulating the passage of materials in and out of cells. Understand diffusion, osmosis, and active transport mechanisms essential to cellular functions.
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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 Fluid mosaic Phospholipid bilayer Protection and support Chemical id tags
Carbohydrate chains Proteins Cell membrane Protein channel Lipid bilayer Figure 7-15 The Structure of the Cell Membrane Section 7-3 Outside of cell Inside of cell (cytoplasm) Go to Section:
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 cellulose Carbohydrate and protein outside
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
Figure 7-17 Osmosis Section 7-3 Water molecules Higher Concentration of Water 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 isotonic osmosis
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 Osmotic pressure hypotonic hypertonic
E.Facilitated Diffusion • 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 Protein channels
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 Energy Go to Section:
