Chp 5_Structure & Function of Plasma Membranes.pptx

Diffusion simple vs facilitated simple diffusion

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DIFFUSION: SIMPLE VS FACILITATED Simple diffusion molecules or ions move directly through the membrane Facilitated diffusion specific transport proteins move solutes across a membrane down their concentration gradient
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OSMOSIS -Is diffusion of water across a differentially-permeable membrane (like plasma membrane) -Is due to solute concentration (like salts) differences inside & outside of cell -Osmosis moves ONLY WATER across the plasma membrane, not solutes (like salts) KEY= understanding the direction that water moves and why!
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OSMOSIS In osmosis, water always moves from an area of higher water concentration to one of lower concentration. In the diagram shown, the solute cannot pass through the selectively permeable membrane, but the water can.
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OSMOSIS - Solute molecules do not pass through the plasma membrane, only water does - The ‘goal’ is to achieve equilibrium - Equilibrium means an equal concentration of solute molecules inside & outside cell - The rule= in osmosis, water moves from regions of low solute to regions of high solute
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OSMOTIC PRESSURE “Most solutes, including ions and sugars, are not lipid-soluble and, therefore, are unable to cross the lipid bilayer. The concentration gradient of these solutes can lead to the movement of water”
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OSMOTIC PRESSURE Determined by concentration of solutes Cells regulate internal osmotic pressure to prevent shrinking or bursting
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TONICITY - Is a description of the relative concentrations of solute inside & outside cells and determines water movement direction - There are 3 forms (we say a solution is _____ relative to the cell): Hypotonic= the solution outside the cell has a lower salt concentration than inside the cell (green dots are solute molecules) Hypertonic= the solution outside the cell has a higher salt concentration than inside the cell (green dots are solute molecules) Isotonic= the solution outside the cell has a equivalent salt concentration to inside the cell (green dots are solute molecules)
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TONICITY Refers to the concentration of SOLUTES Isotonic (equal salt) equal solute concentration Hypertonic (more salt) cell loses water to surroundings Hypotonic (less salt) water enters, cells swell
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THE EFFECTS OF TONICITY HAVE A SIGNIFICANT IMPACT ON RBC STRUCTURE! Osmotic pressure changes the shape of red blood cells in hypertonic, isotonic, and hypotonic solutions. (credit: Mariana Ruiz Villareal) The solution
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THE EFFECTS OF TONICITY HAVE A SIGNIFICANT IMPACT ON PLANT CELLS, TOO! The turgor pressure within a plant cell depends on the tonicity of the solution that it is bathed in. (credit: modification of work by Mariana Ruiz Villareal)
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ACTIVE TRANSPORT - Unlike passive transport that doesn’t require without ATP, active transport is movement of molecules across the plasma membrane using ATP - Often occurs by moving solutes against the concentration gradient P P carrier protein Outside Inside ATP To move against the gradient cells use ATP… And the carrier proteins move molecules in one direction!
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