The Effect of the Type of Bag on the Rate of Diffusion

Nick GudePeriod 3

M. Pietrangelo

Problem Statement and Hypothesis

• Which brand of bag will have the slowest diffusion rate?

• Will the results prove significant enough to be able to claim that that brand(s) has the best plastic content?

• If different brands of bag are used then they will have different amounts of time for diffusion to occur.

• Prediction– Ziploc-Slowest Rate– Giant-Normal Rate– Hefty-Fastest Rate

Basic Concepts

• Diffusion: the primary method of short distance transportion in a cell and cellular systems; a cell’s means of transporting things such as food to and from other cells (Ordom, McCandless). – Materials pass through pores in the membrane

from high to low concentration. • Indicator: usually visual sign that change has

occurred in an experiment.

Design Diagram• IV: Brand of Bag

• DV: How long (in minutes) it takes for the starch in the bag to diffuse with the iodine solution outside.

• Constants: room temp., container size, plastic bag size, amounts of iodine and starch solutions for each trial.

• Materials: Ziploc, Giant, and Hefty bags, three glass bowls, graduated cylinder, water, cornstarch, iodine, transfer pipette, timer.

Level Ziploc Hefty Giant

Trials 10 10 10

Design Diagram cont. (Procedure)1. In each bowl: 1L of water + 20 ml of iodine.2. In each bag: two tsp. starch and fill bag halfway

with water.3. Put one of each brand with added ingredients

into its respective bowl.4. Start timer and observe.5. Once evidence of diffusion is seen (a purplish-

black color), record the time for that trial in data table.

6. Ten trials for each brand.

Results: DataLevels Ziploc Giant Hefty Diffused?

(Y/N)Trial 1 31.33m 20.33m 20.58m yesTrial 2 31.38m 19.96m 20.5m yesTrial 3 31.46m 17.55m 18.46m yesTrial 4 30.95m 17.66m 19.25m yesTrial 5 31.42m 18.08m 18.31m yesTrial 6 31.4m 17.7m 17.18m yesTrial 7 30.98m 20.2m 18.33m yesTrial 8 31.5m 22.75m 18.93m yesTrial 9 31.4m 20.16m 20.01m yesTrial 10 31.35m 18.65m 19.13 yesAverage 31.53m 19.5m 19.12m

Average Diffusion Rates

• Ziploc: Sum of all trial times divided by number of trials (10) = 31m 32s avg.

• Giant: Sum of all trial times divided by number of trials (10) = 19m 30s avg.

• Hefty: Sum of all trial times divided by number of trials (10) = 10m 7s avg.

Graph of Diffusion Rate Averages

31m 32s

19m 30s

19m 7s

Statistical Analysis• 2 Sample T-tests were used to determine if the

results of the experiment were significant.• Ziploc T Tests to both Giant and Hefty both

resulted in low probability of chance (p < .0001)

• The results were significant, and it could be claimed that Ziploc will always have a slower diffusion rate than the other two.

Brand p - valueZiploc vs. Giant 1.06 X 10^-9 (zero)

Ziploc vs. Hefty 8.48 X 10^-12 (zero)

Hefty vs. Giant .35 (could go either way)

Statistical Analysis cont.

• Based off the information gathered from the results of the experiment, it is safe to say that the original hypothesis that each bag would have a different diffusion rate is rejected, since although Ziploc’s time was proven to always be slower, Giant and Hefty could go either way.

Me with my materials, 11/4/10

Me starting the first trial, 11/13/10

Me holding up a diffused bag, 11/14/10

Results Explanation• The diffusion rate is related to the number and

size of the pores in each bag brand.

• Ziploc had a slower diffusion rate, therefore less or smaller pores in the plastic.

• Hefty and Giant had relatively equal diffusion rates, therefore a relatively equal size and amount of pores.

Sources of Error• Not refilling the bowls with fresh iodine for

every trial could have slowed down the diffusion time for a few trials.

• The bowls were not completely identical, and this could have affected the diffusion rate.

• Iodine to size of bag ratio: experiments found online used smaller, thinner sandwich bags, which could have slowed down what would have been the regular diffusion rate for the bags.

Possible Improvements/Extentions

• For each trial, use a freshly mixed iodine and water solution.

• Submerge each bag as much as possible, perhaps get deeper containers.

• Using more iodine in the solution to compensate for the type of bags used.

Applications

• Model/Simulation of simple cellular diffusion.– Used by many schools already for exactly that

purpose.• Could perhaps influence people’s decisions

about which brand of plastic bag is best, maybe an indicator that Ziploc has better quality plastic.

Acknowledgements/Thank You’s

• Parents

• Miss Pietrangelo

• The people who accepted my project

• And YOU