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Molecules to pass o each channel specific for a

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molecules to pass o Each channel specific for a certain molecule - Carrier transport proteins o Have binding sites that attach to specific molecules on one side of the membrane and then move them through to the other side Movement definitions: fluid, solute, solvent, concentration, gradient, diffusion - Fluid = a substance whose molecules can flow past one another and, therefore, have no defined shape - Solute = a substance that can be dissolved (dispersed as atoms, ions, or molecules) in a solvent (e.g. salt or sugar) - Solvent is a fluid capable of dissolving a solute (e.g. water) - Concentration = the amount of solute in solvent o The more solute in a solvent, the higher the concentration o The less solute in a solvent, the lower the concentration - Gradient = a physical difference in temperature, pressure, charge, or concentration between two adjoining regions of space o Molecules in fluids move in response to gradients o Gradients cause molecules to move from one region to another to equalize the difference o Want to reach “equilibrium” o Important for us because concentration gradients of molecules exist on both sides of plasma membranes (inside and outside cell) o Gradients determine what moves in or out of a cell - diffusion = Random motion produces a net movement from regions of high concentration to regions of low concentration 2 movement types: passive & energy-requiring - Passive transport = the diffusion of substances (across cell membranes) down concentration gradients o Simple, no energy required o 3 types - Energy-requiring transport requires the use of cellular energy o 3 types 3 types passive, 3 types energy-requiring - Passive:
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o 1- Simple diffusion : substances move down a concentration gradient (high to low) across a membrane Molecules that move by simple diffusion include oxygen, carbon dioxide, and lipophilic molecules (e.g. alcohol, vitamins A, D, and E) o 2- Facilitated diffusion : small molecules (e.g. salts, amino acids, sugars) diffuse down a concentration gradient with the help of a transport protein (channel or carrier) Specialized channel proteins called
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