Lab 7: Diffusion and OsmosisName:
Prelab

Introduction: Dialysis tubing allows molecules to diffuse through microscopic pores in the tubing. Molecules smaller than the pores can diffuse through the dialysis membrane along their concentration gradients while molecules larger than the pore size are prevented from crossing the dialysis membrane.

Go to Biology Place and step through the LabBench Activity on Diffusion. Then answer the questions below.

Vocabulary Matching

Choose oneConcentration gradientdiffusionosmosishypertonichypotonicisotonicsolutesolvent /
  1. The net movement of molecules down their concentration gradient.

Choose oneConcentration gradientdiffusionosmosishypertonichypotonicisotonicsolutesolvent /
  1. The difference in concentration of solutes in a solution between two regions.

Choose oneConcentration gradientdiffusionosmosishypertonichypotonicisotonicsolutesolvent /
  1. Dissolving substance in a solution

Choose oneConcentration gradientdiffusionosmosishypertonichypotonicisotonicsolutesolvent /
  1. Substance that is dissolved in a solution

Choose oneConcentration gradientdiffusionosmosishypertonichypotonicisotonicsolutesolvent /
  1. Diffusion of water

Choose oneConcentration gradientdiffusionosmosishypertonichypotonicisotonicsolutesolvent /
  1. The solution with lower solute concentration

Choose oneConcentration gradientdiffusionosmosishypertonichypotonicisotonicsolutesolvent /
  1. The solution with higher solute concentration

Choose oneConcentration gradientdiffusionosmosishypertonichypotonicisotonicsolutesolvent /
  1. Two solutions equal in solute concentration

Concept 2: Osmosis

  1. Water moves from concentration of water to a concentration of water.
  1. Water moves from concentration of solute to a concentration of solute.

Concept 3: Movement of Molecules in Solution

  1. How will you know whether the iodine solution has crossed the dialysis membrane?

Concept 5: Types of Solutions Based on Solute Concentration

  1. Will there be a net movement of water between two isotonic solutions?
  2. Water moves from solution to a solution.

Concept 6: Water potential

  1. Why don’t red blood cells pop in the bloodstream?
  1. What happens if an animal cell is placed in distilled water?
  1. What happens if a plant cell is placed in distilled water?
  1. Why is the outcome different for a plant verses an animal cell?

Don’t read Concept 7: Calculating Water Potential or Concept 8: Factors that Affect Water Potential.

Exercise 1

  1. Which of these substances are expected to pass through the dialysis membrane:

Water:

Glucose:


IKI:

Starch:

Exercise 2:

In the following situations, assume that sucrose cannot diffuse through the dialysis membrane.

  1. A dialysis bag containing a 0.20 M solution of sucrose is placed in a beaker of distilled water (the sucrose cannot pass through the membrane). Will the dialysis bag gain or lose mass? Explain why.

Exercise 3:

Contents of Beaker / Initial Mass in grams / Final Mass in grams / Percent Change in Mass
0.0M / 22.0 / 27.0
0.2M / 24.6 / 26.4
0.4M / 23.5 / 23.2
0.6M / 23.7 / 20.4
0.8M / 19.9 / 15.6
1.0M / 21.3 / 16.2
  1. Calculate the percent change in massusing the equation below and record it in the table above:
  1. Graph the sucrose molarity in the beaker and the percent change in mass of the potatoes using xy scatter plot in Excel. Paste the graph below.

  1. At what molarity does the line cross the X axis?
  1. What does that number mean?