Passive Transport

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  • This diagram represents what happens to a red blood cell and plant cell under different solute concentrations. Hypertonic  higher external solute concentration than within the cell so water moves out of the cell Isotonic  equal solute concentrations within and without Hypotonic  higher internal solute concentration that outside of cell so water moves into cell QUESTION #5: Why doesn’t the plant cell burst under hypotonic conditions like the red blood cell?


  • 1. No Bellringer This Week
  • 2. Agenda
    • NOTES: Membrane Transport
      • Membrane Structure
        • Fluid-Mosaic Model
        • Phospholipid Structure
      • Diffusion
        • Solutions
        • Diffusion Gradient
      • Osmosis
        • Isotonic, Hypertonic, and Hypotonic Solutions
        • Cell Shrinking or Bursting
  • 3. Function of the Cell Membrane
    • All cells are surrounded by a thin, flexible barrier known as the cell membrane.
    • In order for a cell to live, molecules must be able to get in and out of the cell.
    • Small molecules (like water) are able to pass directly through the membrane, while large molecules require some help.
  • 4. Structure of the Cell Membrane
    • The structure of the membrane is sometimes described by the “fluid-mosaic” model.
    • This is because the membrane is composed of many different types of molecules.
      • Lipids
      • Protein
      • Carbohydrates
  • 5.  
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  • 7.  
  • 8. The Lipid Bilayer
    • Membranes are made of a double-layered sheet of phospholipids called the lipid bilayer.
    • This bilayer is “selectively permeable”, meaning it lets some molecules through, but not others.
    • Phospholipid molecules have 2 parts:
      • Hydrophilic Head (Polar, Attracted to Water)
      • Hydrophobic Tails (Nonpolar, Repelled by Water)
  • 9.  
  • 10.  
  • 11.  
  • 12.  
  • 13. Solutions
    • A solution is a mixture of a liquid and solid.
      • The liquid is called the solvent
      • The solid is called the solute
    • For example, in a solution of saltwater:
      • Water = Solvent
      • Salt = Solute
  • 14. Diffusion
    • When substances are dissolved in a solution they will spread out evenly.
    • This process of spreading is called diffusion.
    • Diffusion requires no energy because it is based on the random movement of molecules.
    • Examples:
      • If you add a single drop of food coloring to a glass of water, the color will spread through the whole glass.
      • If someone farts on one side of the room, the smell spreads out to everyone around him.
  • 15.  
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  • 18. Diffusion Gradient
    • When a substance is clumped in one area we say that it has a high concentration, while the area with less substance has a low concentration.
    • Diffusion always moves a substance from areas of High Concentration to Low Concentration.
    • This tendency to move from high to low is called “following the concentration gradient”.
      • High Concentration  Low Concentration
  • 19. Passive Transport
    • Diffusion moves molecules in and out of the cell
    • This takes no energy so it’s called “Passive Transport”
    • Diffusion Example
      • As the cell uses oxygen the concentration inside the cell drops. More oxygen flows in from the high concentration outside of the cell.
      • As carbon dioxide builds up inside the cell, this high concentration causes molecules to flow towards the lower concentration outside the cell.
  • 20.  
  • 21. BrainPOP: Passive Transport
  • 22.  
  • 23. Osmosis
    • Osmosis is the diffusion of water
    • The Rule for Osmosis is “SALT SUCKS”
      • Inside of the cell is salty = sucks water in
      • Outside of the cell is salty = pulls water out
  • 24.  
  • 25. Osmosis Terminology
    • Isotonic – the concentration of solutes is the same inside and outside of the cell
    • Hypertonic – the higher concentration of solute
    • Hypotonic – the lower concentration of solute
    • If there is less solute inside the cell then you would say that the cell is Hypotonic and the outside of the cell is Hypertonic.
  • 26.  
  • 27. Effects of Osmosis on Cells
    • If a cell is placed into a Hypertonic solution, the solutes outside the cell will suck out water and cause the cell to shrivel.
    • If a cell is placed into a Hypotonic solution, the solutes inside the cell will attract water and cause the cell to burst.
    • Note that plant cells will not burst because the membrane pushes up against the cell wall.
  • 28.  
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  • 30.  
  • 31. Assignment
    • 19 Review Questions
    • Due Tomorrow