Classroom copy – Complete Lab on Loose-leaf

Cell Transport and Dialysis Lab

I. Background: Cell Transport; What is Dialysis?

Cells placed in solutions with varying concentrations of solute and water will respond depending on the type of solution. This is due to passive transport in the form of osmosis. Dialysis is the diffusion of solute molecules across a differentially permeable membrane. The cell membrane is differentially permeable. Thus, through dialysis, certain substances may enter a cell, and certain metabolic products, including wastes, may leave. Depending on the permeability of a membrane, small solute molecules may pass through, while larger molecules are held back. Utilizing this principle, it is through dialysis that artificial kidney machines remove the smaller waste particles from the human bloodstream.

Pre-lab questions

1) Explain water movement and concentration gradients within:

a) a hypotonic solution

b) a hypertonic solution

c) an isotonic solution

2) What type of environment (hypo, hyper, or iso) does an animal cell prefer? Explain.

3) What type of environment (hypo, hyper, or iso) does a plant cell prefer? Explain.

4) What is the purpose of dialysis?

II. How do we see it?

The following experiment demonstrates the separation of different-sized molecules by dialysis. The two molecules used are starch (a large molecule) and sodium chloride (salt, a small molecule). In order to determine the presence of each of these molecules, we must be able to test for them.

III. What indicators are we using?

Sodium chloride (NaCl) plus silver nitrate (AgNO3) produces a dense white precipitate. Iodine is an indicator for starch in the presence of starches it produces a blue-black color.

IV. Materials

150 ml BeakerScissorsPaper Towel

50 ml beakerDistilled Water

15 % NaCl solution 10ml graduated cylinder

Dialysis Tubing 20 cmAgNO3 (silver nitrate)

Iodine solution (Lugol’s works well)1 % Starch (corn starch) solution

V. Procedure:

  1. Obtain a length of dialysis tubing 20 cm.
  2. Soak the tubing in water for 3 minutes.
  3. Using your finger rub the open end back and forth until it opens up, and then blow some air into it.
  4. Tie off one end with a double knot, making sure the knot is at the end of the tubing.
  5. Fill the bag with 3 ml of starch solution, and 3 ml of sodium chloride solution.
  6. Gently squeeze the air out, and tie off the top.
  7. Rinse the ‘cell’ off in tap water, and briefly place it on a paper towel.
  8. Now, place the ‘cell’ in the beaker, and note the time. Add 5 drops of Iodine solution to the beaker of water containing the bag.
  9. After 30 minutes, remove the cell and place it back onto the paper towel.
  10. Obtain a sample of the liquid from the 150 ml beaker and place itin the 50 ml beaker. Test the 50 ml beaker with 2 drops of silver nitrate.
  11. Record your results from the liquid and the added indicators into to the table below.

Color / Before / After 30 minutes or adding indicator
Liquid Inside of Cell
Liquid Outside of Cell
Liquid in 50 ml beaker

VI. Cell Transport

At Lab station 1 are 3 eggs that have been soaked in vinegar to remove their shell. The acetic acid of the vinegar reacts with the calcium carbonate of the shell to create carbon dioxide, thus breaking down the shell. One of these eggs has been placed in corn syrup, another has been placed in tap water, and a third in distilled water. Without removing the eggs from the solution, make careful observations of each egg and the type of solution it is in. Fill in the chart below.

Type of Solution / Observations / Hypo-, Hyper-, or Isotonic

VI. Questions:

1.What happened with the cell? Explain any color change that may have happened.

2. Where did the precipitate form? Why did it occur?

3. Explain the analogy of our make shift cell and that of cells in the body going through dialysis treatments.

4. Create a diagram that uses arrow to show the movement of molecules from the experiment. Include in the diagram; water, iodine, starch, NaCl.

5. Based on your results, rank the following molecules according to size: iodine, starch, NaCl, pores of the dialysis tubing.

6. What would have happened if we had started this experiment with the starchsolution in the beaker rather than the “cell”?

7. Explain how you determined if the egg was in a hypo-, hyper-, or isotonic solution.