Diffusion of Carbon Dioxide Through Gelatin Lab: A Model for Diffusion of Nanoscale Particles Through Cells—Pupil Pages-

Jennifer Welborn

KABA’S

You should know:

1. What diffusion is and what factors affect the rate of diffusion.

2. That diffusion is one of the ways that materials move into and out of cells.

You should be able to:

1.Explain how and why this lab is a model for diffusion of carbon dioxide through cells

2.Conduct a controlled experiment of CO2 diffusing through gelatin.

3.Use a digital camera as a tool to collect data on color change over time.

4.Use ADI software to analyze images you get from the experiment.

Research Questions: Can a digital camera be used to quantify a change in the color of BTB in gelatin as carbon dioxide (carbonic acid) diffuses through it?What affect might a change in the concentration of CO2 or temperature have on the rate of diffusion of CO2 through the gel? How is diffusion related to cell size?

Background

Diffusion is a process, which involves movement of a substance from a region of its higher concentration to a region of its lower concentration.


Diffusion is used to reach equilibrium: a condition in which the concentration of a substance is equal throughout a space. Dissolved particles that are small or non-polar can diffuse through cellmembranes. The process of diffusion is one of the ways in which substances like oxygen, carbon dioxide and water move into and out of cells.

The rate of diffusion can be affected by various factors: temperature; particle size; concentration of the diffusing material, density of the material through which a material diffuses. Diffusion happens more quickly in higher temperatures. Large particles diffuse more slowly.

When carbon dioxide is mixed into water, carbonic acid is created. A substance called bromothymol blue (BTB) can be used to indicate the presence of carbonic acid. It is called an acid-base indicator. A change in color of BTB from blue to yellow indicates the presence of an acid. In this lab, BTB will indicate that CO2 is diffusing through gelatin. This activity is a model for how CO2 diffuses through cells.

Setting up the CO2 Diffusion Experiment

Preparation

  1. Trace the bottom of the large Petri dish (centered) onto white paper. In the center of the circle on the paper, draw a 2.5 cm x 2.5 cm square.
  2. Tape the paper down on the lab bench.
  3. Set up the tripod/ring stand to enable consistency of data collection over time.
  4. This setup will be referred to as the camera station.

Experiment

  1. Using a knife, cut out 3 gelatin cubes, each being 2.5 cm on an edge (2.54 cm3). Make 3 labels:

Time: O minutes
Control—no CO2 / Time: 30 minutes
CO2 / Time: 1 hour
CO2
  1. Using a sharp knife, cut a 5 mm thick slice from the middle of one of the cubes, creating a piece of gelatin which is .5 x 2.5 x 2.5 cm.
  2. Place the gelatin slice in the middle of the petri dish and put the dish on the white paper at the camera station lining it up with the circle that was drawn. Move the gelatin as needed so that it lines up with the corresponding square you drew as well. Arrange the label (control, 0 minutes) so that it will be included in the photo.
  3. Take a picture (with the flash off).
  1. Place the other 2 cubes into 2 separate jars. Fill each jar with seltzer water to the brim. Put lids on each jar so the CO2 cannot escape.
  2. After 30 minutes, open one of the jars, take out the gelatin block and repeat steps 2-4 making sure to include the (CO2, 30 minutes) label in the photo.
  3. Repeat steps 2-4 with the other (CO2, 1 hour) experimental setup.
  4. Refer to the specific steps in the lab instructions for how to use the ADI line tool to both quantify and qualify the diffusion of CO2 through the gelatin over time.

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Questions to Consider

  1. How did the control data differ from the experiment data?
  1. Diffusion is related to concentration and temperature. What affect might

an increase in atmospheric CO2(due to increased burning of fossil fuels) have on

the rate of CO2 diffusion in cells?

  1. What affect might an increase in temperature have on the rate of CO2

diffusion in cells?

  1. What do you notice about the diffusion of CO2 through the gelatin over time?
  1. How do you suppose the rate of diffusion is related to cell size?
  1. What do the RGB values and color graphs show you about diffusion?
  1. Predict how the R, G, B, values and the color graph would look if you let the gelatin cube stay in the same seltzer water overnight. Test this out and see.
  1. Predict how the results might change if you refreshed the carbonated water every ½ hour. Test and see!
  1. Which is a more accurate model of diffusion of CO2 in cells over time: step #7 or step #8? Explain.

Extensions/Challenge

1.Design and conduct a similar experiment to test the effect of changing the

temperature or concentration of CO2 on the rate of diffusion of CO2.

2. Experiment with different sizes of gelatin blocks. How does this relate to cell size? (Why must cells be small?).

3. When you make a color graph, turn off all colors but the blue or green. Measure each of these over time and create graphs. What do you notice from the graph?

4. Make gelatin of different densities and test the effect of media density on rate of diffusion.

Check for Understanding:

Reread the KABA’s to make sure you know and are able to do the major concepts/skills of this lab.