Sept. 14, 2012

5. Movement into and out of cells. Remember, the cell membrane is a phospholipid bilayer.
     -What are the ways that substances can move into a cell?

     A. Diffusion - the idea that a substance moves from a high to a low concentration, or in other words, it moves down a concentration gradient. (So if you jump out of a tree, you will fall and hit the ground. Same thing like a cell.)
     - Examples:
          - O2, most cells needs oxygen.
          - CO2, requires no energy expenditure. (ATP) The greater the concentration difference the greater the force of diffusion.
     B. Osmosis - the diffusion of H2O. There are a couple of tricks to the diffusion of water. Water is polar, you can't just diffuse the membrane, so it diffuses through special H2O channels (proteins) called aquapurins. Do all cells have these? Yes. Water is absolute necessity for all cells.
     -H2O always moves from a low solute concentration (Hypotonic) to a high solute concentration (Hypertonic). Movement will stop when the two solutions are equal in concentration (Isotonic).
          - Scenario: Say you have a beaker of sugar solution. The sugar is a 1.0 molar sucrose. (To say the something is 1 mole, it's a mole per liter, so this is really sweet!) There is a cell in that solution. (the solution of sucrose is 0 mole) Can the sucrose move through the cell membrane? No, it's way to big to get through that membrane. What direction will the water move, into or out of? Water will move out of the cell. So then osmosis is backwards from a diffusion? False, we're talking about the diffusion of water. Water is at 100% concentration in that cell. Water is moving from a high water concentration to a low water concentration. When will the water movement stop? That's a trick question. It will never stop. The movement of water will only stop when the cell is completely dehydrated.