Name:______Block:______Date:______

Virtual Osmosis and Diffusion Lab Activities

Lab Activity #1: Movement Across a Membrane

Log on to: http://web.archive.org/web/20130504172034/http://bioweb.wku.edu/courses/Biol114/Osmosis/Osmosis1.asp

Directions: Read through the website and conduct the activity by following the instructions. (Typically you press the red dot to advance the activity.) Answer the questions on this paper as you move through the activity.

What did you place INSIDE the dialysis bag? ______

What did you place in the beaker OUTSIDE of the dialysis bag? ______

______

The following table describes the indicators that are used to test for different substances.

Test

/ Positive Result /

Negative Result

IKI (iodine) test for starch / dark blue/purple/black solution / no color change or amber solution
Barium chloride (BaCl2) test for sulfate(SO4) ions / milky or cloudy white precipitate formed / no color change or no precipitate
Silver nitrate (AgNO3) test for chloride (Cl-)ions / milky or cloudy white precipitate formed / no color change or no precipitate
Biuret test for protein / light purple solution / no color change or light blue solution

Enter “+” or “-“ for each test :

Results of Tests for Substances in Beaker

Initially / After incubation

Starch

Sulfate ion
Chloride ion
Protein

Results of Tests for Substances in Bag

Initially / After incubation

Starch

Sulfate ion
Chloride ion
Protein

Follow-up Questions:

1) To which substances was the dialysis tubing permeable?

A.  Starch/sulfate ion

B.  Starch/protein

C.  Chloride ion/sulfate ion

D.  Protein/chloride ion

2) To which substances was the dialysis tubing impermeable?

A.  Starch/sulfate ion

B.  Starch/protein

C.  Chloride ion/sulfate ion

D. Protein/chloride ion

3) Suggest a reason for the failure of some substances to diffuse through the membrane. Hint: The chemical formula for sulfate is S04 and for starch (C6H10O5)700. ______

______

4) Can different materials diffuse through a membrane in opposite directions at the same time? Support your statement with evidence from your experiment. ______

______

______

5) In what way is the dialysis membrane like the cell membrane? ______

______

______

6) In each case, the molecules moved from ______concentration to ______concentration.

7) Dialysis is a technique used to purify blood in cases of kidney failure. During dialysis, what substances would you want to remove from the bloodstream? What substances would you want to remain in the bloodstream? Hint: You may have to look up how dialysis works online.

______

______

______