Kristin CoadIB Biology 2September 2010

Effect of diffusion through semi-permeable membrane

INTRODUCTION:

Diffusion occurs when molecules of a high concentration move to a low concentration. This is more formerly known as moving down the concentration gradient. The objective of diffusion is to reach equilibrium or where everything is equal (refer to figure one). In this research, the relationship between the rate of diffusion through a semi-permeable membrane and surface area of dialysis tubing which is filled with starch will be investigated. Because of the nature of the membrane, this enables diffusion to occur. The results which would be tested is the colour of the starch after being in the water based iodine solution for five minutes. A colourmeter is the main device that would help to record the colour reading. The colourmeter is a piece of equipment which tests for the accurate amount of light that is being absorbed in a solution. The reading of the starch will happen after the meter is calibrated with water and starch. This has to happen to get a base reading of no absorbance, and the regular absorbance of starch. Distilled water came up with a reading of 99.9 nanometres, where as the starch had a reading of 90.5 nanometres (The light colourmeter is read in nanometers, and the light being used for this experiment is a blue-violet light with a reading of 430 nanometers). The transmittance, or how much light is being absorbed in a solution, is what was being tested for this experiment. The way that the colour was tested was by having the same amount of starch, 10 milliliters, in three different size dialysis tubing bags; the average lengths were 194.75mm, 80mm, and 35mm and the height of all the bags were 45mm, which was all submerged in the same bath of water/ iodine solution. Because of the chemical reaction, when starch is diffused with water/iodine, the end colour will turn up to be in the purple spectrum.

What is expected to happen during this experiment is that the bags that have smaller surface area should diffuse slower, rather than the longer bags, which take less time to diffuse. The obvious way that the colour will be figured out is by the how dark or light the end reaction is.

It is predicted that at the end of the five minutes, the longer bags will have a darker, more prominent purple colour, rather than the small surface area that will be around a light purple, and nearly see-through. This is because thelarger bags have less starch per square centimeter, so it would be almost like diffusing less liquid at one time, instead of more starch like in the little bags.

Figure 1: This is a diagram of basic diffusion. As labeled, the water molecules between the membrane on the right are equal, or have reached equilibrium because the

Question: How does the amount of surface area affect the rate of diffusion through a semi-permeable membrane?

Independent variable: Surface area of the semi-permeable membrane

Controlled variables How it was controlledI2KI For each trial being in the same bucket so the

iodine is the same for each tube.

Time Setting a time, and having a “set time” of five minutes

Amount of Starch Measuring five milliliters in a graduated cylinder, measuring at the bottom of the meniscus.

Width of dialysis tubing By using the same roll of dialysis tubing, and by measuring one to get the size.

Temperature of water Putting the tubing in the same large bucket filled with water and iodine simultaneously for all the trials for each length.

Dependent variable- The time in which the cell takes to reach equilibrium by passing through the membraneTable 1: The controlled variables of the experiment.

Table 1: This table shows all of the different controlled variables that went into the experiment. Along with that, the table shows how they were being controlled through-out the entire experiment.

MATERIALS:

Semi-permeable membrane (dialysis tubing), 3 different lengths x4

Ruler Scissors Water Bucket Iodine Starch Computer Colourmeter Curvettes Clamps Funnel Graduated cylinder Stop watch Beaker

PROCEDURE:

Semi-permeable membrane

Figure 2: This figure shows some of the materials that were being used through out the experiment. Part of the materials includes the ruler, scissors, and the semi-permeable membrane.

Before the research began, three different lengths of semi-permeable membrane was measured with a ruler and cut four times to create 4 trials. All of the tubes were soaked in plain water for a few minutes so they can be opened. The three lengths averages were 194.75mm, 80mm, and 35mm. After every membrane was cut and tied at one end only, five millimeters of starch was poured into each bag via funnel. Then all the air remaining in the bag was squeezed out to help add to the accuracy of the results. While the bags were being filled and measured, the bath containing the water and iodine mix solution was being prepared. The bucket was large enough to be able to hold 12 bags. To ensure that the bags would not stick to each other, slight agitation was necessary, while a partner on the computer set up and calibrated the colour meter. Once everything was calibrated with water and starch samples, and the five minutes of agitation was over, each bag is opened one by one, poured into a curvette via funnel. Each bag was tested in the colourmeter to get an average reading for each of the three lengths. Once all of the curvettes were measured, and the data recorded, everything was cleaned up, and put back where it belonged.

HYPOTHESIS:

It was predicted that the bag with the smallest surface area to amount of starch would take more time to diffuse through the semi-permeable membrane. It was predicted like this because since the bag is completely full of starch, it would take longer for everything to completely diffuse. Where as, the bags with more surface area wont need as much time because the starch would pan out, and then there would be less starch in one area. Because of the starch to iodine reaction, it is expected that the starch will be tinted a purple- blue colour after some time, and the end colour of all the three different size bags won’t differ too much.

Figure 3: This figure shows the set up of the colourmeter (on the left) with the computer (on the right) to record the transmittance.

DATA:

Table 2: Recorded average lengths and transmittance (Uncertainty of ± 0.05)

Size of the bagTrials (length of bag in mm)

Average length Transmittance (colourmeter in nanometers)

Average transmittance

Small 1.214 2. 1903. 187 4. 184

193.75

1.11.2 2. 10.93. 14.0 4. 10.7

11.625

Medium 1.80 2. 813. 80 4. 79

80

1.38.7 2. 39.63. 36.14. 34.4

43.95

Large 1.362. 353. 334. 32

34

1.63.72. 65.13. 69.04. 67.2

66.25

Table 2: This data table represents the relationship between the length of the membranes and colour for each of the four trials. The table includes four trials of each of the three lengths (small, medium and large), and the transmittance of each of the trials. Also included in the table are the averages of the length and transmittance. The bags were measured in millimeters, and the transmittance was measured in nanometers.

Figure 4: The water/iodine bath with the three different sizes. All four trials are submerged with in the one bucket. This is before diffusion happened.

Figure 5: This is the after photo of the starch semi-permeable membrane baggies. Diffusion has occurred due to the purple-blue stain.

Graph 1: The relationship between the average length and transmittance (Uncertainty ± 0.05)

Graph 1: The graph above shows the relationship between the average length of the membrane and transmittance of light. As the membrane length increases, the transmittance decreases. This means that for instance, the membrane with 193.75mm of surface area, the transmittance is low. In other words, the darker the colour after diffusion, the less percent of transmittance there.

CONCLUSION/EVALUATION:

The way that surface area affects the rate of diffusion is by amount of surface area. In the research, there were different size bags of semi-permeable membrane, though they all contained the same amount of starch inside. What ended up was that the bag with the most surface area, 200mm, took shorter than five minutes to fully diffuse, where as the bag that was completely full of starch would have taken longer than the given five minutes to finish fully diffusing. The research does not fully support the hypothesis in the sense that what it explained about the time because of the surface area was correct. What was not supported was the colour factor being that the end product resulted in drastically different shades of the purple stain in the starch. After the five minutes in the bath, the bag that had the smallest surface area, average of 34mm, had the weakest colour of 66.25 nanometers. After that, the medium bag of 80mm had the transmittance of 43.95 nanometers, and lastly, the longest bag of 193.75mm had the littlest transmittance of 11.625 nanometers. The biggest bag that had the lowest nanometer reading was the darkest all the bags, then the medium, and the smallest bag.

Things that could be improved for the next experiment include things such as accurate readings, lengths and sample sizes. For the evaluation, refer to table three.

Table 3: Observations through-out the experiment

Qualitative observations The immense difference of colour between the three different bags. Maybe if the smallest bag was the size of the longest bag, then the colour would be darker, or close to the same range.

Quantitative observations Things such as the temperature could have affected the end result of the colour, but since every bag was in the same bucket of room temperature, all the bags received the same temperature.

Another observation that was taken account for is the amount of starch in the bags. Since there was the amount in every bag was 10 mililetres, this greatly took a role in how the results came out.

Another observation was the amount of time the bags were in the solution. They were in the bath for five minutes giving each set of bags to diffuse in the amount of time that was given.

Table 3: The table above shows the qualitative observations such as colour, and the quantitative observations like temperature and amount of starch through out the experiment.

Figure 6: The above figure shows the four trials after diffusion. The liquid is presented in curvettes which were all sampled in the colourmeter.

Table 4: Table of weaknesses and limitations of the experiment

Weakness/ limitations What(how it was effect it) SolutionLength Because rulers are unreliable,

this made it hard to get a very accurate measurement.

Perhaps to use something that accurately measures the length of the membrane.

Ruler This weakness is by not having very accurate equipment.

Requesting to have better measuring equipment.

Sample size This weakness was made because of the uncertainty of how long each different piece should have been.

Take longer sample sizes. Instead of making the first one short, by making it longer and going from there will improve the experiment.

Table 4: This table shows the weaknesses and limitations that were faced through-out the experiment. It also shows how it affected the experiment, and the solution towards fixing it.

This is a lab that I did on diffusion in the beginning of biology SL. This lab was to see the how the length of a semi-permeable membrane effects the rate of diffusion. The outcome was that the longer pieces diffused faster. The major WoK in this lab is reason. The way that reason partakes in this lab is because, if the data cannot be read right, then a reasonable conclusion cannot be processed.