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CELL TRANSPORT
• Cell membranes are similar to a mesh bag or a screen on a window.
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What Does This Have To Do With Cells???
• To survive, cells must take in nutrients and eliminate waste materials.
• To do this, nutrients and waste materials must cross the cell membrane between the solution outside of the cell, and the solution inside the cell.
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What type of Membrane?
• Semi permeable membrane: allows certain molecules to pass through and prevents others from passing.
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Semi Permeable Cell Membrane
• Small molecules like water can enter and leave the cell freely.
• Larger molecules such as proteins and carbohydrates cannot enter and leave the cell freely due to their size.
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Transportation Processes (2)
• Transport = movement of a substance across a cell membrane
• Passive Transport: without energy.
• Active Transport: uses energy
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Passive Transport (3 types)
• Simple Diffusion
• Facilitated Diffusion
• Osmosis
All three involve the movement of a substance across a cell membrane without the input of the cell’s energy.
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Factors To Consider (2)
• Diffusion always occurs from a high concentration to a low concentration.
• A concentration gradient is the difference between the concentration of a particular molecule in one area and its concentration in an adjacent area.
• When molecules have been dispersed evenly, there is no concentration gradient, an equilibrium has been reached, and diffusion stops.
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Simple Diffusion
Initially, the concentration of a substance outside the cell is higher than the inside.
Later, the substance has diffused into the cell so that the concentration is the same on both sides of the membrane.
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If a lump of sugar is dropped into a beaker of water, the molecules dissolve (A) and diffuse (B and C).
Eventually, diffusion results in an even distribution of sugar molecules throughout the water (D).
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Facilitated Diffusion
• Molecules diffuse across a cell membrane with the HELP of carrier proteins in the membrane.
• Always move from a higher level of concentration to a lower level.
• Allows the glucose molecule into the blood cells.
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Facilitated Diffusion
During facilitated diffusion, carrier proteins shuttle molecules across the lipid bilayer of the cell membrane.
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Facilitated Diffusion
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Osmosis
• The diffusion of water across a semi permeable membrane
• Again water moves down its concentration gradient.
• Moves from higher water concentration to lower water concentration.
WATER
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Osmosis
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Active Transport
Uses cellular energy to move substances across the cell membrane. Against a concentration gradient – from a low concentration to a high concentration.
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The Sodium Potassium Pump
• Active transport is especially important in maintaining the ion concentration in cells.
• Ex: Animal cells pump sodium ions out and potassium ions into the cell.
• High concentration of sodium ions outside of the cell.
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Sodium Potassium Pump
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Exocytosis
• Moves material too big to fit through the cell membrane from a low concentration to a high concentration.
• The vesicles then fuse with the cell membrane and the materials in the vesicles is secreted out of the cell.
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Endocytosis
• The process by which a portion of the cell membrane surrounds a desirable macromolecule that is outside of the cell. Moves from a low concentration to a high concentration.
• The cell then pinches off the saclike portion of its outer membrane to form a tiny new vesicle.
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Desired macromolecules
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Three tumor cells being engulfed by a white blood cell!