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This resource explains the process of passive transport in the plasma membrane, including diffusion and osmosis. It covers the establishment of equilibrium, the movement of molecules across the membrane, and the regulation of water flow.

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  1. Resources Chapter Presentation Visual Concepts Transparencies Standardized Test Prep

  2. Plasma Membrane Homeostasis and Cell Transport Table of Contents Section 1 Passive Transport Section 2 Active Transport

  3. Plasma Membrane Passive Transport Objectives • Explain how an equilibrium is established as a result of diffusion. • Distinguish between diffusion and osmosis. • Explainhow substances cross the cell membrane through facilitated diffusion. • Explain how ion channels assist the diffusion of ions across the cell membrane.

  4. Passive Transport Section 8.1 Summary – pages 195 - 200 • When a cell uses no energy to move particles across a membrane passive transport occurs. Concentration gradient Plasma membrane

  5. Plasma Membrane Passive Transport Concentration Gradient Click below to watch the Visual Concept. Visual Concept

  6. Plasma Membrane Passive Transport Diffusion • Diffusionis the movement of molecules from an area of higher concentration to an area of lower concentration, driven by the molecules’ kinetic energy until equilibrium is reached. • Diffusion Across Membranes • Molecules can diffuse across a cell membrane by dissolving in the phospholipid bilayer or by passing through pores in the membrane.

  7. Plasma Membrane Passive Transport Diffusion

  8. Plasma Membrane Passive Transport Osmosis • Osmosisis the diffusion of water across a membrane. • In a cell, water always moves to reach an equal concentration on both sides of the membrane. • Regulating the water flow through the plasma membrane is an important factor in maintaining homeostasis within a cell.

  9. Plasma Membrane Passive Transport Osmosis Click below to watch the Visual Concept. Visual Concept

  10. What controls osmosis? Before Osmosis After Osmosis Section 8.1 Summary – pages 195 - 200 • Unequal distribution of particles, called a concentration gradient, is one factor that controls osmosis. Selectively permeable membrane Water molecule Sugar molecule

  11. Passive Transport Plasma Membrane • Direction of Osmosis • The net direction of osmosis is determined by the relative solute concentrations on the two sides of the membrane. • Solute: in a solution, the substance that is dissolved in the solvent • i.e. Sugar in sugar water

  12. Plasma Membrane Passive Transport Osmosis

  13. Plasma Membrane Passive Transport Hypertonic, Hypotonic, Isotonic Solutions

  14. Plasma Membrane Passive Transport • Direction of Osmosis - hypertonic • When the solute concentration outside the cell is higher than inside the cell, the solution outside ishypertonicto the inside of the cell, and water will diffuse out of the cell.

  15. Cells in a hypertonic solution Section 8.1 Summary – pages 195 - 200 • In a hypertonic solution, water leaves a cell by osmosis, causing the cell to shrink. H2O H2O Water Molecule Dissolved Molecule

  16. Cells in a hypertonic solution Section 8.1 Summary – pages 195 - 200 • Plant cells lose pressure as the plasma membrane shrinks away from the cell wall.

  17. Plasma Membrane Passive Transport • Direction of Osmosis - isotonic • When the solute concentrations outside and inside the cell are equal, the solution outside isisotonic, and there will be no net movement of water.

  18. Cells in an isotonic solution Section 8.1 Summary – pages 195 - 200 • Most cells whether in multicellular or unicellular organisms, are subject to osmosis because they are surrounded by water solutions. H2O H2O Water Molecule Dissolved Molecule

  19. Cells in an isotonic solution Section 8.1 Summary – pages 195 - 200 • In an isotonic solution, the concentration of dissolved substances in the solution is the same as the concentration of dissolved substances inside the cell. H2O H2O Water Molecule Dissolved Molecule

  20. Cells in an isotonic solution Section 8.1 Summary – pages 195 - 200 • In an isotonic solution, water molecules move into and out of the cell at the same rate, and cells retain their normal shape.*** H2O H2O Water Molecule Dissolved Molecule

  21. Cells in an isotonic solution Section 8.1 Summary – pages 195 - 200 • A plant cell has its normal shape and pressure in an isotonic solution.

  22. Cells in a hypotonic solution Section 8.1 Summary – pages 195 - 200 • In a hypotonic solution, water enters a cell by osmosis, causing the cell to swell. H2O H2O Water Molecule Dissolved Molecule

  23. Cells in a hypotonic solution Section 8.1 Summary – pages 195 - 200 • Plant cells swell beyond their normal size as pressure increases.

  24. Plasma Membrane Passive Transport Comparing Hypertonic, Isotonic, and Hypotonic Conditions Click below to watch the Visual Concept. Visual Concept

  25. Plasma Membrane Passive Transport • How Cells Deal With Osmosis • Contractile vacuolesare organelles that regulate water levels in paramecia.

  26. Plasma Membrane Passive Transport Facilitated Diffusion – carrier proteins • In facilitated diffusion, a molecule binds to a carrier protein on one side of the cell membrane. • The carrier protein then changes its shape and transports the molecule down its concentration gradient to the other side of the membrane.

  27. Passive Transport by proteins Section 8.1 Summary – pages 195 - 200 Channel proteins Concentration gradient Plasma membrane

  28. Passive Transport by proteins Section 8.1 Summary – pages 195 - 200 • Some transport proteins, called carrier proteins, form channels that allow specific molecules to flow through. Channel proteins Concentration gradient Plasma membrane

  29. Passive transport by proteins Section 8.1 Summary – pages 195 - 200 • The movement is with the concentration gradient, and requires no energy input from the cell. Carrier proteins Concentration gradient Plasma membrane Step 1 Step 2

  30. Passive transport by proteins Section 8.1 Summary – pages 195 - 200 • Carrier proteins change shape to allow a substance to pass through the plasma membrane. Carrier proteins Concentration gradient Plasma membrane Step 1 Step 2

  31. Passive transport by proteins Section 8.1 Summary – pages 195 - 200 • In facilitated diffusion by carrier protein, the movement is with the concentration gradient and requires no energy input from the cell. Carrier proteins Concentration gradient Plasma membrane Step 1 Step 2

  32. Plasma Membrane Passive Transport Passive Transport: Facilitated Diffusion Facilitated diffusionmov

  33. Plasma Membrane Passive Transport Facilitated Diffusion

  34. Plasma Membrane Passive Transport Diffusion Through Ion Channels • Ion channelsare proteins, or groups of proteins, that provide small passageways across the cell membrane through which specific ions can diffuse.

  35. Plasma Membrane Passive Transport Ion Channels

  36. Plasma Membrane Passive Transport Diffusion Through Ion Channels Ion Channelsmov

  37. Plasma Membrane Active Transport Objectives • Distinguishbetween passive transport and active transport. • Explain how the sodium-potassium pump operates. • Compareendocytosis and exocytosis.

  38. Plasma Membrane Active Transport Active Transport • Active transportmoves molecules across the cell membrane from an area of lower concentration to an area of higher concentration, moving against the concentration gradient. • Unlike passive transport, active transport requires cells to expend energy.

  39. Active Transport Section 8.1 Summary – pages 195 - 200 • Movement of materials through a membrane against a concentration gradient is called active transport and requires energy from the cell. Carrier proteins Concentration gradient Plasma membrane Cellular energy Step 1 Step 2

  40. Plasma Membrane Active Transport Cell Membrane Pumps • Some types of active transport are performed by carrier proteins called cell membrane pumps.

  41. How active transport occurs Section 8.1 Summary – pages 195 - 200 • In active transport, a carrier protein called a cell membrane pump first binds with a particle of the substance to be transported. Carrier proteins Concentration gradient Plasma membrane Cellular energy Step 1 Step 2

  42. How active transport occurs Section 8.1 Summary – pages 195 - 200 • Each type of carrier protein has a shape that fits a specific molecule or ion. Carrier proteins Concentration gradient Plasma membrane Cellular energy Step 1 Step 2

  43. How active transport occurs Section 8.1 Summary – pages 195 - 200 • When the proper molecule binds with the protein, chemical energy allows the cell to change the shape of the carrier protein so that the particle to be moved is released on the other side of the membrane. Carrier proteins Concentration gradient Plasma membrane Cellular energy Step 1 Step 2

  44. How active transport occurs Section 8.1 Summary – pages 195 - 200 • Once the particle is released, the protein’s original shape is restored. • Active transport allows particle movement into or out of a cell against a concentration gradient. Carrier proteins Concentration gradient Plasma membrane Cellular energy Step 1 Step 2

  45. How active transport occurs Section 8.1 Summary – pages 195 - 200 Click image to view movie.

  46. How active transport occurs Section 8.1 Summary – pages 195 - 200 Click image to view movie.

  47. Plasma Membrane Active Transport Cell Membrane Pumps • Sodium-Potassium Pump • The sodium-potassium pumpmoves three Na+ ions into the cell’s external environment for every two K+ ions it moves into the cytosol. • ATP supplies the energy that drives the pump.

  48. Plasma Membrane Active Transport Sodium-Potassium Pump

  49. Plasma Membrane Active Transport Sodium-Potassium Pump Sodium-Potassiumpump mov

  50. Plasma Membrane Active Transport Movement in Vesicles • Endocytosis • In endocytosis, cells ingest external materials by folding around them and forming a pouch. • The pouch then pinches off and becomes a membrane-bound organelle called a vesicle.

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