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Membrane

Plasma. Membrane. I. MAINTAINING BALANCE. How do cells maintain balance? Cells need to maintain a balance by controlling material that move in & out of the cell  HOMEOSTASIS. I. MAINTAINING BALANCE.

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Membrane

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  1. Plasma Membrane

  2. I. MAINTAINING BALANCE • How do cells maintain balance? • Cells need to maintain a balance by controlling material that move in & out of the cellHOMEOSTASIS

  3. I. MAINTAINING BALANCE • Smallmolecules like water, oxygen, and carbon dioxide can move in and out of the cellfreely. • Largemolecules like proteins and carbohydrates cannot. • Eliminating wastes

  4. I. MAINTAINING BALANCE

  5. STRUCTURE of the PLASMA (CELL) MEMBRANE • All cells are surrounded by a plasma membrane. • Functions like a GATE, controlling whatENTERSand LEAVES the cell. • The cell membrane is semipermeable or selectively permeable.

  6. STRUCTURE of the PLASMA (CELL) MEMBRANE • A semipermeable membraneonly allows certain molecules to pass through • Some substances easily cross the membrane, while others cannot cross at all.

  7. STRUCTURE of the PLASMA (CELL) MEMBRANE • Made of a thin layer of lipids and proteins • Made mostly of phospholipidmolecules (Phosphate + Lipid). • Phospholipids are a kind of lipid that consists of 2 FATTY ACIDS (tails), and PHOSPHATE GROUP (heads).

  8. STRUCTURE of the PLASMA (CELL) MEMBRANE • Cell membranes consist of TWO phospholipid layers called a LIPID BILAYER. 

  9. Phosphate Head Cytoplasm Lipid Tail Phosphate Head STRUCTURE of the PLASMA (CELL) MEMBRANE

  10. STRUCTURE of the PLASMA (CELL) MEMBRANE • Water molecules surround both sides of the cell membrane.  • Polar phosphate heads sticking toward the water (hydrophilic) • Nonpolarlipid tails pointing away from the water (hydrophobic).

  11. Cytoplasm STRUCTURE of the PLASMA (CELL) MEMBRANE • The cell membrane is constantly being formed and broken downin living cells.

  12. III. LIPID BILAYER • Moving with and among the phospholipids are cholesterol, proteins, and carbohydrates. • Cholesterol: • Nonpolar, found among the phospholipids to help prevent the fatty acid tails from sticking together • Helps w/ structure and homeostasis

  13. III. LIPID BILAYER

  14. III. LIPID BILAYER • Proteins: • Found on the surface of the plasma membrane = transmit signals to the inside of cell • Embedded in the plasma membrane = structure and support of cells shape, and move large substance in and out of the cell

  15. III. LIPID BILAYER

  16. III. LIPID BILAYER • Carbohydrates: • Attached to proteins, helps cells identify chemical signals • Ex: help disease fighting cells recognized and attack a potentially harmful cell

  17. Cellular Transport

  18. Cellular Transport • All particles move and have kinetic energy (energy of motion). • Movement israndom and usually in a water solution. • Cells are mostly made of water and there is a constant flow of ions and particles.

  19. IV. 2 TYPES OF CELLULAR TRANSPORT 1. Passive transport = movement of molecules across the membrane by using the molecules kinetic energy. The cell exerts noenergy! 2. Active transport = transport of materials against the concentration gradient and requires cellular energy.

  20. V. PASSIVE TRANSPORT • 3 types of passive transport: 1. Diffusion = the net movement of particles from an area of HIGHER concentration of particles to an area of LOWER concentration of particles.

  21. Diffusion…. • Molecules move randomly until they are equally distributed. • Diffusion continues until the concentration of substances is uniform throughout.

  22. Diffusion…. • Dynamic equilibrium = continual movement but no overall change in concentration; • Movement of materials into and out of the cell at equal rates maintains its dynamic equilibrium with its environment.

  23. Diffusion…. • Diffusion depends on the concentration gradient. • Concentration gradient is the difference between the concentration of a particular molecule in one area and the concentration in an adjacent area. • Ex: gas exchange in the lungs (oxygen from air to blood and carbon dioxide from blood to air)

  24. V. PASSIVE TRANSPORT 2. Facilitated Diffusion = type of passive transport that increases the rate of diffusion with the use of carrier proteins. • Ex: Facilitated diffusion of glucose

  25. Facilitated Diffusion

  26. V. PASSIVE TRANSPORT 3. Osmosis = the diffusion of watermolecules from an area of HIGH water concentration to an area of LOW water concentration.

  27. V. PASSIVE TRANSPORT: OSMOSIS • Occurs in response to the concentration of solutes dissolved in water! • Solutes are dissolved substances in a solution. • Cytoplasm is mostly water containing many dissolved solutes.

  28. V. PASSIVE TRANSPORT: OSMOSIS • Because no TWO molecules can occupy the same space at the same time, the MORE solutes there are in a certain volume of water; the FEWER water molecules there can be in the same volume.

  29. V. PASSIVE TRANSPORT: OSMOSIS • Plant and animal cells behave differently b/c plant cells have a large water vacuole and a cell wall. Plant Animal Cell

  30. V. PASSIVE TRANSPORT: OSMOSIS • Ex: Osmosis occurring in a slug (animal) cell

  31. V. PASSIVE TRANSPORT: OSMOSIS A. Isotonic solution = a solution in which the concentration of dissolved substances (solutes) is the SAME as the concentration of solutes inside the cell. • Osmosis does not occur since a concentration gradient is not established!

  32. What happens to cells when placed in an isotonic solution? • Plant cell–becomes flaccid (limp) • plant wilts b/c no net tendency for water to enter • Animal cell- normal

  33. Animal Cell Plant Cell

  34. V. PASSIVE TRANSPORT: OSMOSIS B. Hypotonic solution = a solution in which the concentration of solutes is LOWER than the concentration of solutes inside the cell.

  35. What happens to cells when placed in a hypotonic solution? • Animal cell- water will move thru plasma membrane into the cell. This causes the cell to swell and the internal pressure increases. • Cell lyses (bursts)!

  36. What happens to cells when placed in a hypotonic solution? • Plant cell- normal • the vacuole and cytoplasm increase in volume. • the cell membrane is pushed harder against the cell wall causing it to stretch a little. • the plant tissue becomes stiffer (turgid).

  37. Animal Cell Plant Cell

  38. V. PASSIVE TRANSPORT: OSMOSIS C. Hypertonic solution = a solution in which the concentration of dissolved substances is HIGHER than the concentration inside the cell.

  39. What happens to cells when placed in a hypertonic solution? • Animal cell - will shrivel b/c of decreased turgor pressure

  40. What happens to cells when placed in a hypertonic solution? • Plant cell- will lose water from vacuole and a decrease in turgor pressure will occur; so it is plasmolyzed. • Turgor pressure = internal pressure of a cell due to water held there by osmotic pressure • Plasmolysis = the loss of turgor pressure causing the plasma membrane to pull away from the cell wall • causes the plant to wilt

  41. Animal Cell Plant Cell

  42. D. Summary of Cell Behavior in Different Environments:

  43. VI. ACTIVE TRANSPORT • Movement of molecules from an area of LOWto an area of HIGH concentration. (opposite of passive transport!) • Requirescellularenergy! • Moves large, complex molecules such as proteins across the cell membrane

  44. VI. ACTIVE TRANSPORT • Large molecules, food, or fluid droplets are packaged in membrane-bound sacs called vesicles

  45. 2 types of active transport: 1. Endocytosis= process by which a cell surrounds and takes in material from its environment • Used by ameba to feed & white blood cells to kill bacteria

  46. Endocytosis

  47. 2 types of active transport: 2. Exocytosis = expels materials out of the cell, reverse of endocytosis • used to remove wastes, mucus, & cell products • Proteins made by ribosomes in a cell are packaged into transport vesicles by the Golgi Apparatus • Transport vesicles fuse with the cell membrane and then the proteins are secreted out of the cell (ex: insulin)

  48. Exocytosis

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