Chapter 5 powerpoint


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Chapter 5 powerpoint

  1. 1. Homeostasis and Cell TransportChapter 5
  2. 2. Passive TransportPassiveTransport – substances cross the cell membrane with NO energy input from the cell
  3. 3. DiffusionDiffusion – movement of molecules from an area of higher concentration to an area of lower concentration ◦ Concentration Gradient – difference in the concentration of molecules across a distance ◦ Molecules tend to move from where they are more concentrated to where they are less concentrated (“down” their concentration gradient)
  4. 4. DiffusionDiffusion is driven entirely by the molecules’ kinetic energy ◦ Molecules are in constant motionDiffusion will eventually cause the molecules to be in equilibrium – the concentration of molecules will be the same throughout the space the molecules occupy ◦ At equilibrium, molecules continue to moveHow Diffusion Works
  5. 5. Diffusion
  6. 6. Diffusion Across MembranesDiffusion Across Membranes ◦ Simple diffusion – diffusion across a cell membrane ◦ Depends on:  Size of molecule  Type of molecule  Chemical nature of the membrane Diffusion Across Membranes
  7. 7. OsmosisWater molecules diffuse across a cell membrane from an area of higher concentration to an area of lower concentration
  8. 8. Direction of OsmosisHypotonic solution – concentration of solute outside the cell is lower than the concentration inside the cell ◦ Water diffuses into the cell
  9. 9. Direction of OsmosisHypertonic solution – concentration of solute outside the cell is higher than the concentration inside the cell ◦ Water diffuses out of the cell
  10. 10. Direction of OsmosisIsotonic solution – concentration of solutes is equal outside and inside of the cell ◦ Water diffuses into and out of the cell at equal rates
  11. 11. OsmosisHow Osmosis Works
  12. 12. How Cells Deal With OsmosisContractilevacuoles – organelles that remove waterSolute pumps – pump solutes out of the cell
  13. 13. How Cells Deal With Osmosis Cellwall in plants resists the pressure exerted by water inside of a cell ◦ Turgor pressure – pressure that water molecules exert against a cell wall ◦ Plasmolysis – cells shrink away from cell walls and turgor pressure is lost
  14. 14. How Cells Deal With OsmosisSome cells cannot compensate for changes in solute concentration ◦ Ex: red blood cells can swell and burst (cytolysis)
  15. 15. Facilitated DiffusionFor molecules that cannot diffuse across cell membranes, even when there is a concentration gradientMovement of molecules is assisted by carrier proteins
  16. 16. Facilitated Diffusion How Facilitated Diffusion Works
  17. 17. Important Properties of FacilitatedDiffusionCan help substances move either into or out of the cell, depending on the concentration gradientCarrier proteins involved in facilitated diffusion are each specific for one type of molecule
  18. 18. Diffusion Through Ion Channels ◦ Ion channels – transport ions such as sodium (Na+), potassium (K+), calcium (Ca2+), and chloride (Cl-) ◦ Some ion channels are always open ◦ Some have “gates” that open and close in response to:  Stretching of the cell membrane  Electrical signals  Chemicals in the cell or external environment
  19. 19. Section 2ACTIVE TRANSPORT
  20. 20. Active TransportMovement of materials from lower concentration to higher concentration (“up” their concentration gradient)Requires energy from the cell
  21. 21. Cell Membrane PumpsSodium-Potassium Pump ◦ transports Na+ and K+ ions up their concentration gradientsHow the sodium-potassium pump works
  22. 22. Steps of the Sodium-PotassiumPump
  23. 23. Steps of the Sodium-PotassiumPump1. Three Na+ ions from the inside of the cell bind to the carrier protein
  24. 24. Steps of the Sodium-PotassiumPump2. A phosphate group is removed from ATP and bound to the carrier protein
  25. 25. Steps of the Sodium-PotassiumPump3. The carrier protein changes shape, allowing three Na+ ions to be released to the outside of the cell
  26. 26. Steps of the Sodium-PotassiumPump4. Two K+ ions from the outside of the cell bind to the carrier protein
  27. 27. Steps of the Sodium-PotassiumPump5. The phosphate group is released and the carrier protein goes back to its original shape
  28. 28. Steps of the Sodium-PotassiumPump6. The two K+ ions are released to the inside of the cell and the cycle is ready to repeat
  29. 29. Importance of the Sodium-Potassium PumpThe ion exchange creates an electrical gradient across the cell membrane ◦ Outside becomes positively charged ◦ Inside becomes negatively chargedThis difference in charge is important for the conduction of electrical impulses along nerve cells
  30. 30. Movement in VesiclesUsed for: ◦ Substances that are too large to pass through the cell membrane ◦ Transporting large amounts of small molecules into or out of cells at the same time
  31. 31. Endocytosis
  32. 32. EndocytosisProcess in which cells ingest external fluid, macromolecules, and large particles, including other cellsTwo types of endocytosis: ◦ Pinocytosis – transport of solutes or fluids ◦ Phagocytosis – transport of large particles or whole cellsEndocytosis
  33. 33. Exocytosis
  34. 34. ExocytosisProcess by which a substance is released from the cell through a vesicle that transports the substance to the cell surface and then fuses with the membrane to let the substance out of the cellExocytosis