The Effect of Surface Area on the Diffusion of Glucose in Potatoes
Michelle Pryce
Biology 106 Section 46
Jenn Rinehart
Abstract
The purpose of this experiment was to determine the effects of surface area on the diffusion rate. Potatoes were used so that the diffusion rate of the glucose out of the potato could be measured. The glucose levels in the solutions were measured using the spectrophotometer. The levels of glucose were tested in order to determine whether or not there was a relationship between the surface area of the potato, and the diffusion rate of the glucose. A diffusion rates of glucose in the potato core with a greater surface area were higher than those with smaller surface areas.
INTRODUCTION
The relationship between surface area and diffusion were examined in this experiment. Diffusion is the random movement of substances from higher to lower levels of concentration, down a concentration gradient. Diffusion occurs until equilibrium is reached. Equilibrium is reached when the molecules that diffused are distributed equally (Mader, 2007). The steeper the concentration gradient, the faster diffusion occurs. The rate of diffusion is also affected by temperature and the size of the diffusing substances. As temperature increases, the rate of diffusion increases as well. As the size of the diffusing substances increases, the diffusion rate decreases (Kaisa, 2008).
The objective of this experiment was to determine the relationship between surface area and the rate of diffusion. The alternative hypothesis was that there is a direct relationship between the surface area and the diffusion rate. The null hypothesis was that there is no relationship between surface area and diffusion rate.
METHODS AND MATERIALS
To begin the experiment three beakers were filled with 15 milliliters of distilled water each. Three potato cores of four centimeters each were then obtained from the same potato. The first core was left at four centimeters. The surface area of this core was calculated using the formula (2Πrh) + (2Πr2), r being the radius of the core and h being the height of the core. The second core was cut into two segments, each two centimeters long. The same formula was used to calculate the total surface area of each of these two centimeter cores. The final potato core was divided into four segments, of one centimeter each. The total surface area of the four remaining cores was then calculated using the above formula.
Each of the three sets of potato cores were placed into one of the beakers containing 15 milliliters of distilled water. Each sample remained in the water for twenty minutes. The allowed time for the glucose from the potato to diffuse down the concentration gradient into the water. After twenty minutes, the potato cores were removed from the beakers and the contents were stirred. One tenth of a milliliter of the remaining substance from each of the beakers was placed into three separate cuvettes. Then a half of a milliliter of o-dianisidine-enzyme solution was added to each cuvette. O-dianisidine was used because it changes color in the presence of the glucose molecule. It becomes darker when put into a solution that contains glucose. A blank was then prepared by placing one tenth of a milliliter of distilled water and a half of a milliliter of o-dianisidine-enzyme solution in another cuvette. A standard was prepared in a separate cuvette using one tenth of a milliliter of glucose standard and a half of a milliliter of o-dianisidine-enzyme solution. All five of the cuvettes were then incubated at thirty-seven degrees Celsius for thirty minutes.
After the samples incubated for thirty minutes the glucose levels were determined using a spectrophotometer. The wavelength was set at 450 nanometers using the nanometer arrows. After the wavelength was set, the cuvette containing the blank was inserted into the spectrophotometer. The blank was then set at zero absorbance by holding down the 0ABS/100%T button. When the blank was set, it was removed and the standard was put in. In order to set the standard, the Standard soft key was pressed and the arrow keys were used to enter the concentration of the standard. Then the Set C soft key was pressed to calculate the factor for the standard. Once the standard factor was established, the standard was removed from the spectrophotometer and the samples were ready to be tested. Each of the three samples was placed into the spectrophotometer and the concentrations were calculated. A chi-square median test was also conducted. This was used to measure whether or not differences in the numbers actually meant anything.
RESULTS
The results of the experiments showed that as the surface area increased, the rate of diffusion also increased. As shown in Table 1, the four-centimeter potato core had a surface area of 957 millimeter2 and a diffusion rate of 0.16 mg/dl/min. The sample composed of two, two-centimeter cores had a total surface area of 1,034 millimeter2 and a diffusion rate of 0.17 mg/dl/min. The final sample of four, one-centimeter cores had a total surface area of 1,188 millimeter2 and a diffusion rate of 0.22 mg/dl/min. These values did differ significantly and the probability (p) value was calculated at greater than ten percent (Table 1).
DISCUSSION
The findings of this experiment did agree with our hypothesis that a greater surface area results in a higher rate of diffusion. The diffusion rate of the core sample that was divided into four pieces was the greatest because there was more area for molecules to pass in and out of. In opposition, the single four-centimeter core sample, with the smallest surface area, had the lowest rate of diffusion.
One weakness of this experiment was time. Time was a weakness because all three of the samples had the same time requirement. They all had to be allowed to sit in the fifteen milliliters of distilled water and diffuse for twenty minutes before being removed. It was difficult to perform this procedure for each of the samples at the exact same time. The cores were removed from the beakers one at a time. This allowed some of the cores to diffuse for a slightly longer amount of time than the others that were removed first. Another weakness of this experiment was measurement. This is a weakness because of human error. The samples had to each sit in exactly fifteen milliliters of water so that they were each in the same amount. If any of the beakers had more water than another, the concentration would be off and the final results would be skewed.
In the future this experiment could be completed using more than three samples. For example, a core larger than four centimeters could be used and divided into many pieces. The glucose diffusion rate of pieces greater than four centimeters and smaller than one centimeter could be measured, providing more data. The greater the number of pieces of core, the greater the surface area of each of the cores. Another thing that could be done in the future is a similar experiment relating the surface area and the rate of diffusion using a sample other than potato cores. The diffusion rate of something other than glucose could be measured. This would provide more information as to whether there is a relationship between surface area and diffusion rate in substances containing samples other than glucose.
LITERATURE CITED
Kaisa, T.R. 2008. Biology 105 Laboratory Manual. Tafadzwa R. Kaisa, Clemson, SC.
Mader, Sylvia S. 2007. Biology. 9th ed. McGraw Hill Press, New York, NY.
Table 1: Relationship between surface area and glucose diffusion rate.
Surface Area and Glucose Diffusion Rate Data
Surface Area (mm2) / Glucose Diffusion Rate (mg/dl/mi)957 / 0.16
1034 / 0.17
1188 / 0.22
P>10%