Diffusion and Osmosis Lab

     Diffusion and Osmosis are very similar and different. In this experiment, we will observe the strengths in their differences.
     As the lab analysis paper says, "molecules only move from regions of higher concentration to lower concentration during diffusion and osmosis. Cells often need to absorb molecules from regions in which concentration of the molecules may be lower than the concentration already inside the cell. The absorption of glucose from blood frequently occurs under these circumstances. Cells use the process of active transport to move substances through the cell membrane against a concentration gradient. Active transport involves proteins in the cell membrane and energy derived from ATP. Diffusion and osmosis do not require any added energy."
     A solution of glucose and starch will be placed inside a bag of dialysis tubing, and we will pour water into the beaker, outside the dialysis bag. We'll let it sit for about 30 minutes, and the solution inside the bialys is tubing and in the beaker were tested for glucose and starch. To test for glucose, we use indicator strips. To test for starch, we use Lugol's solution (iodine and potassium iodide) Starch appears to be a bluish-purple complex with iodine, and glucose does not.

	Initial Contents	Initial	Final	Initial	Final
Bag	15% Glucose $ 1% Starch	Clear	Clear and Black	+	+
Beaker	H2O + IKI	Yellow and Brown	Clear	+	+

1. How would you explain the results you obtained? Which substances are entering the bag and which are leaving the bag?

    I believe that the water from the outside of the bag started to seep into the bag. I believe this because a color change, or chemical reaction, took place. I know that such a thing wouldn't happen unless the solution was mixed with another.

2. What evidence could have been collected to show quantitatively that water diffused into the dialysis bag?

    The amount of water outside the bag, and inside the bag. These measurements could have been taken before and after the experiment.

3. What results would you expect if the experiment started with a glucose and IKI solution inside the bag and only starch and water outside?

    The results would be different because the IKI would have mixed differently with the glucose solution than the simple water and iodine mixture did.

Cell Membrane Notes

The plasma membrane is common to all cells
Separates:
  Internal living cytoplasmic from
  External environment of cell
Phospholipid bilayer:
  External surface lined with hydrophilic polar heads
  Cytoplasmic surface lined with hydrophilic polar heads
  Non polar, hydrophobic, fatty-acid tails sandwiched between

MEMBRANE MODELS
Fluid-Mosaic Model
Three components:
  Basic membrane referred to as phospholipid bilayer
  protein molecules
    float around like icebergs on a sea
    Membrane proteins may be peripheral or integral
      Peripheral proteins are found on the inner membrane surface
      Integral proteins are partially or wholly embedded (transmembrane) in the membrane
    Some have carbohydrate chains attached
  Cholesterol

How does it do its job?
How does it let stuff through?

It's like a perfume being sprayed. Once the particles get into the air, they spread out more. That's why people across the room can smell just one spray of perfume!

Diffusion: Movement from high concentration to low concentration

Osmosis: diffusion of water across a membrane

What CAN go across a cell membrane WILL go across!

When it is warmer, the molecules move faster. So when it's colder, they must move slower and it's tougher for them to move around.