1. SIMULTANEOUS OSMOSIS AND DIFFUSION USING A CELL MODEL
BIOLOGY 156,
TUESDAY June 8, 2010,
SOPHIA HINOJOSA
INTRODUCTION:
Diffusion is the movement of molecules from areas of high
concentration of solutes to areas of lower concentration of solutes, down to a
concentration gradient. Diffusion occurs through air, water, gels and the
membranes surrounding cells because it is a universal process. Osmosis is
the movement of water molecules across a semi permeable membrane from
areas of low concentration of solutes to areas of higher concentration of
solutes. In order for molecules to exit or enter a cell, they pass through the
plasma membrane, selectively permeable structure that lets some solutes
move through easily and other solutes with more difficulty. Some using
diffusion and others requires energy for their movement. If water
concentration gradient exists across a cell membrane, osmosis occurs and
cell volumes change. These are the three terms to describe effects of
osmosis on cell volumes:
1. Hypertonic, solution that contains more solute and less water than a
cell’s cytoplasm which causes it to shrink.
2. Hypotonic, solution which contains less solute and more water than a
cell’s cytoplasm which causes it to swell.
3. Isotonic, solution which contains equal amounts of solute and water as
the cell’s cytoplasm which neither shrink nor swell.
METHODS:
In the lab exercise, we examined the movement of water, starch,
Na2SO3, NaC1 and albumin (protein) through the dialysis membrane. The
first thing we did was add 50 mL of beaker solution and 150 mL of distilled
water into the beaker. The solution now contained 0.5% Na2SO4 (sodium
sulfate) and 0.25% starch. Record the contents of the beaker in the data
chart by using a positive or negative. The next thing to do is get a piece of

2. dialysis tubing and soak in water. Then tie a clip to one end and filled the
bag ¾ full with the bag solution containing 1% albumin and 3% Nac1
(sodium chloride). Secure the bag and record the contents by placing a
positive or negative in the appropriate space. It is important to weigh and
record the weight of the bag. Then, immerse the bag into the contents of the
beaker for about 1 hour. After the hour has passed, remove the bag, weigh
and record it a second time. Pour the contents onto the 100ml beaker. Now
for the chemical testing, there will be four tests to perform. Get a total of 8
tubes, 4 for the contents in the bag, and 4 for the beaker. There should be
equal amounts of the solution in the 4 bag tubes as well as the 4 beaker
tubes.
Using one tube from each set, add one drop of iodine (IKI) to the
first set. A blue black color is a positive test for starch. Record the results as
(+) or (-) in the appropriate space. Next is a drop of barium chloride
(BaC12) to the second tube of each set. A faint white precipitate of BaSO4 is
a positive test for SO4 (sulfate ion). Record the results as (+) or (-) in the
appropriate space. Next dip an Albustix into the third tube of each set. The
paper will turn green or green blue for a positive test. Record the results as
(+) or (-) in the appropriate space. The last test is to add one drop of silver
nitrate (AgNO3) to the fourth tube of each set. A milky white precipitate of
AgC1 (silver chloride) is a positive test for C1 (chloride ion). Record the
results as (+) or (-) in the appropriate space.
RESULTS:
After reviewing the data, the starch did not diffuse and the chloride
went from bag to beaker. The weight of the bag changed because the
solution inside the beaker had a lower concentration and that’s why it gained
weight.
CONCLUSION:
Beaker: .75 solute, 99.25% solvent
Bag: 4% solute, 96% solvent