Tube solute incubation 1 01 m kmno4 4o c 2 01 m

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: e the stoppers 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. origin solute front diffusion distance false 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. Modeling Osmosis: 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 movement. Procedure: 1. Each table should obtain 2 – 400 ml beakers and...
View Full Document

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.

Ask a homework question - tutors are online