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and incubate each tube at the condition specified for
that tube. Record the time.
4. After at least one hour, use a ruler to measure the
diffusion distances of the solutes (see Fig. 1) and
record these measurements in your lab notebook.
Diffusion rate = distance moved (mm) / time (min.)
5. Remove the stoppers from the tubes and place them in
the designated recycling container. Dispose of the
tubes in the designated waste container. Tube
# Solute Incubation 1 0.1 M KMnO4 4o C 2 0.1 M KMnO4 room temp. 3 0.1 M KMnO4 35o C 4 0.1 M An.Blue room temp. 5 0.02 M An.Blue room temp. 6 0.01 M An.Blue room temp. Table 1.
solute front diffusion
solute front clear
agar Analysis. First, describe how these variations in molecular
mass, solute concentration, and temperature influenced
diffusion rate and then offer an explanation for these results
based upon what you have learned about diffusion. Figure 1. Measurement of diffusion distance.
This diagram approximates the appearance of
a sample tube after the allotted incubation time.
Diffusion distance will be the distance between
the origin at the top of the agar and the solute front.
Ignore any false solute fronts that may appear
because the solute moved between the agar and
the wall of the tube. Biology 05LA – Fall Quarter 2012 Lab 3 – page 3 OSMOSIS.
Many cell types experience situations where the total solute concentration is different on the
inside and the outside of the cell. When this occurs, water can move into or out of the cell depending
upon the relative concentration of solutes on either side of the membrane. These water movements can
have a significant influence upon cell volume or upon the level of hydrostatic pressure within the cell.
In animals, osmotically driven water movement can drive many important secretory events such as
sweating. However, in other animal cells, large changes in cell volume can be detrimental. In plants,
osmotically driven water movement can contribute to a “skeletal” system that supports young plant
parts or drive bulk solute flow through the plant. Given the diverse ways that these water movements
influence both plants and animals, an understanding of the mechanism enabling this movement is
essential to the biology student.
This study will also introduce another expression of solute concentration called osmolarity. As
you should know, a 1 molar solution of a polar molecule like glucose contains 6.02 x 1023 molecules of
glucose per liter of solution. However, when 1 mole of a salt like NaCl is combined with water to
make a 1 molar solution, the NaCl dissociates to give 1 mole of sodium ions (Na+) and 1 mole of
chloride ions (Cl-). The dissociation thus doubles the total solute concentration of this solution.
Consequently there are twice as many solute molecules in this solution that can deplete the total
potential energy of the water molecules in the solution. As a result, the osmotic effect of a 1.0 M NaCl
solution is twice that of a 1.0 M solution of a polar molecule. Osmolarity is an expression of
concentration that accommodates this situation. Here, what needs to be understood is that the
osmolarity of a solution is an expression of the total concentration of solutes expressed as molarity.
For example, a 1.0 M solution of NaCl has an osmolarity of 2 osmolar and a 1.0 M solution of
CaCl2 has an osmolarity of 3 osmolar. Given this information, it follows that osmotic water movement
will occur in response to differences in osmolarity but not necessarily to differences in molarity.
In this experiment, we will create “artificial cells” with the use of a synthetic differentially
permeable membrane (called dialysis tubing). By filling these artificial cells (“dialysis bags”) with
solutions of varying concentration and then placing them in beakers with solutions of varying
concentration, we can model the osmotic challenges imposed upon real cells by changes in internal and
external solute concentrations. Table 2 lists the 4 conditions that will be tested.
Constructing these dialysis bags is fairly simple. Dry, precut strips of dialysis tubing are
soaked in a beaker of distilled water. The strip is removed from the water and one end of the strip is
tied tightly with a short piece of string. The other end is then opened in a manner comparable to
opening the plastic bags in the produce section of the supermarket. Once opened, the desired solution
is put into the bag. The bag is then closed by tying a knot with one end of a longer piece of string. A
piece of colored tape is attached to the free end of the string and marked with the appropriate number.
The bag is then weighed and placed in the specified incubation solution. After one hour, the bags are
reweighed to determine if water has moved into or out of the bag. In this manner should see how
differences in solute concentration on either side of a membrane affect the direction of osmotic water
1. Each table should obtain 2 – 400 ml beakers and...
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This note was uploaded on 08/27/2013 for the course BIO BIOL05LA taught by Professor Abbottl during the Fall '12 term at UC Riverside.
- Fall '12