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Transcript
Cell boundaries Objectives Identify the main functions of the cell membrane and the cell wall Describe what happens during diffusion Explain the processes of osmosis, facilitated diffusion, and active transport The cell membrane The cell membrane is a thin, flexible barrier that regulates what enters and leaves the cell The cell membrane is made up of a double layered sheet, called a lipid bilayer Model of a cell membrane Diffusion Diffusion is the tendency of particles to move from an area of high concentration, to an area of low Diffusion relies on random particle movement, therefore, diffusion requires no energy This process will continue until the system reaches what is called equilibrium – The concentration of the solute is the same through out the system Osmosis What is osmosis? – – – Osmosis is simply diffusion of water through a selectively permeable membrane A membrane is considered selectively permeable if it some things can pass through it but not others All biological membranes are selectively permeable Does osmosis require energy? Concentration The concentration of a solution is the mass of a solute in a given volume, or mass/volume A solution is made up of 2 parts, a solute and a solvent – – Solute is the substance that is being dissolved Solvent is the substance that is doing the dissolving Isotonic solutions When talking about equilibrium within a cell, we say the concentrations of the solute are the same within the cell, as they are outside In this case, the solutions are said to be isotonic, or “same strength” Hypertonic vs hypotonic solutions While a solute is diffusing across a membrane, that solute is moving from an area of high concentration to an area of low The solution containing the greater concentration is called hypertonic, or “above strength” and the solution containing the lower concentration is called hypotonic Facilitated diffusion This is the movement of specific molecules across a cell membrane using protein channels (transport proteins) This is a fast and specific form of diffusion, but it is still diffusion – therefore it must follow the rules of diffusion ([high]>[low]) and doesn’t require energy Glucose molecules Facilitated diffusion High Concentration Cell Membrane Low Concentration Protein channel Active transport When a cell needs something, but cannot use diffusion, it must use energy 2 of the ways this energy is used are: 1 – Small molecules are “pumped” across a membrane by transport proteins 2 – Larger molecules are moved across the membrane using endocytosis and exocytosis A large part of the energy a cell has is used in supporting these forms of transport Endocytosis Endocytosis – This is the process of bringing material into the cell using infoldings or pockets of the cell membrane and forming a vacuole within the cell There are 2 forms of endocytosis 1. 2. Phagocytosis Pinocytosis Exocytosis In this type of active transport, use of energy to remove material from the cell A contractile vacuole is an example of this Pinocytosis In this form of endocytosis, pockets of liquid form along the cell membrane – They then “pinch” off within the cell to form a vacuole This is also known as cell drinking Phagocytosis This process can be thought of as “cell eating” It happens when a cell engulfs a particle and packages it within a vacuole Amoebas use this form of transport to acquire food Terminology cell membrane cell wall concentration lipid bilayer diffusion equilibrium osmosis isotonic hypertonic hypotonic facilitated diffusion endocytosis phagocytosis pinocytosis exocytosis