Brogan Walters
Higher osmolarity in sweet potatoes than ordinary potatoes
Biology 182 Lab, Thursday 11:00am
Lab 5 Osmosis, Dialysis and Diffusion Laboratory
10/1/14

Introduction: Osmosis is the diffusion of water across a semi-permeable membrane. (1) This process depends on the difference of concentrations of solutes on each side of the membrane. In this experiment the osmolarity of two types of potatoes were compared, the sweet potato and the ordinary potato. The sweet potato is more nutrient dense than a normal potato, in that it has more sugar, fiber and vitamins than a normal potato.(3) The hypothesis is the sweet potato will have a higher osmolarity than the ordinary potato because of its more nutrient dense nature. The ordinary potato will see an increase also but not to the magnitude of the sweet potato.
Methods:
Fifteen potato cores were prepared from both the sweet and ordinary potato and trimmed to be 1cm long. Each core was weighed using a balance and set aside for later in the experiment, keeping them organized. There were five different solutions; 25 mL were placed in each beaker. For each type of potato 15 beakers were used, three for each of the known solutions. When each beaker was ready, one of the weighed cores was placed into each of them. Time was recorded when submersion commenced. After 45 minutes, the cores were pulled out and patted dry to resemble the starting moistness. Each core was weighed for the final weight. The data was used to calculate the average percentage change in weight. The controls in the experiment were the size of the potato, immersion time in the solution and the amount of each solution.

Results Ordinary potato | 0.15 mOsm | 0.20 mOsm | 0.25 mOsm | 0.30 mOsm | 0.35 mOsm | Initial average weight (g) | 1.074 | 1.043 | 1.054 | 1.072 | 1.033 | Final average weight (g) | 1.090 | 1.095 | 1.041 | 1.099 | 1.014 | % change | 1.45% | 5.07% | -1.22% | 2.47% | -1.80% |
Table 1: The average initial and final weights of ordinary potatoes with the percent change Sweet potato | 0.15 mOsm | 0.20 mOsm | 0.25 mOsm | 0.30 mOsm | 0.35 mOsm | Initial average weight (g) | 0.783 | 0.764 | 0.779 | 0.766 | 0.776 | Final average weight (g) | 0.876 | 0.842 | 0.838 | 0.850 | 0.839 | % change | 11.87% | 10.23% | 7.56% | 10.87% | 8.06% |
Table 2: The average initial and final weights of sweet potatoes with the percent change

Figure 1: Percentages of weight change in each solution of ordinary and sweet potatoes In Table 1, the average initial and final masses for the ordinary potatoes are displayed with the calculated percentage change. The largest increase in mass percentage was in the 0.20 mOsm solution at 5.07%. The largest decrease in mass was at the 0.35 mOsm solution at -1.80%. There were three solutions that gained mass and two solutions
Table 2 shows the average initial and final masses for the sweet potatoes with the calculated percentage change. The largest increase in mass was in 0.15 mOsm solution with 11.87% increase. There were only gains in mass with the sweet potato for all five solutions. The smallest increase was at 0.25 mOsm with 7.56% increase. Figure 1 displays the data from Tables 1 and 2 using a line graph. The ordinary potato is shown with the blue line and has lower values and some in the negative. The red line shows the data for the sweet potato and has much higher values than the ordinary potato with no values in the negative.

Discussion: The hypothesis was supported in the osmosis experiment; the sweet potato did have a higher rate of osmolarity than the ordinary potato. The sweet potato in all the different conditions always increased in weight, but with different percentages. This shows that the solution’s water concentration was higher compared to the sweet potato, so it was transferred to the sweet potato. More research would have to be done to see which solutes in the sweet potato caused this, but it can be inferred because of the more nutrient dense nature of the sweet potato compared to the ordinary potato. (3) The biggest mass gain was in the 0.15 mOsm solution with 11.87% increase. As the solution became more concentrated the increase in weight gradually went down ending at 8.06%. There is a 7.56% increase at 0.25 mOsm, but this could be considered an error because with diffusion there should be a linear relationship. The normal potato increased at three of the solution and decreased with two of the solutions. The largest increase in mass was at 0.20 mOsm with 5.07%. The largest decrease was at 0.35mOsm with -1.80%. This data was confusing because there is no sense of a linear relationship. It fluctuates back and forth between increasing and decreasing mass, the composition of the potato stays the same and the solutions continue to increase in concentration. The ordinary potato should have had the biggest increase at 0.15 mOsm like the sweet potato. This could be user error and the final potatoes were not dried to resemble the initial potato moistness. The use of different tools could have ensured a more consistent sample size and weight. Possibly to improve the results, the solution could be weighed instead of the core. A common problem was how much to dry the potato cores, but if the cores were removed with caution the solution could be weighed to measure gain/loss of mass. The greatest error with this experiment though is that there was no control. There was no pure solution that had no sucrose, so the data for how each type of potato reacts in pure water remains unknown. This makes the experiment very weak and hard to base any kind of conclusion besides the relative osmolarity between the two types of potatoes.
References
1. Caprioglio, H., Luscombe, C., Righini, S., and Brown, P. (2014). “Osmosis, dialysis, and diffusion laboratory (vanden huevel, 2006).” Bio 182L Fall 2014 Lab Manual 25-27. 2. Wellness Team. (2013). “White potatoes vs. sweet potatoes: which are healthier?.” Cleveland Clinic. http://health.clevelandclinic.org/2013/03/white-potatoes-vs-sweet-potatoes-which-is-healthier/.