How do ph levels affect diffusion of starch in a sweet potato cell? A Great Student. Biology 111. October 12, Mrs. Stewart

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1 How do ph levels affect diffusion of starch in a sweet potato cell? A Great Student Biology 111 October 12, 2016 Mrs. Stewart

2 Abstract The agriculture of sweet potatoes can be massively affected by the ph of the soil the potatoes are placed in. There have been very few experiments done to study what ph level is best for sweet potatoes. In this experiment, my team and I soaked five sweet potato cores in different ph s in ten minute intervals and weighed the cores in between the intervals. The trend found from the data was that all five ph s caused the cores to gain weight which did not support my hypothesis, but ph 7 affected the core the least and ph 2 affected the core the most. One fatal error made in the experiment was accidentally using a yam instead of a sweet potato, which can be attributed for the odd results.

3 Diffusion and osmosis occur in a multitude of organisms and help balance out many substances within and outside of organisms. Diffusion, by technical definition, is the movement of particles of any substance so that they spread out into the available space (Reece et al., 2014). Diffusion occurs down the concentration gradient, thus requiring no energy (Reece et al., 2014). Any type of transport across a biological membrane that does not require energy is considered passive transport (Reece et al., 2014). There are many specific types of diffusion. The most important type is osmosis, which is the movement of water across a membrane down its concentration gradient (Reece et al., 2014). The main goal is for the movement of free water to reach equilibrium where the net movement of water across a membrane is zero, or happening in both directions at the same rate (Reece et al., 2014). Osmosis is directly related to tonicity (Reece et al., 2014). There is isotonic, hypertonic, and hypotonic s. Isotonic s have no net movement of water in or out of the cell (Reece et al., 2014). Hypotonic s cause a cell to take in water faster than the cell can diffuse the water back out (Reece et al., 2014). Lastly, hypertonic s cause a cell to lose water faster than the cell can intake water (Reece et al., 2014). In animal cells, a hypotonic causes the cell to lyse or explode, while a hypertonic causes a cell to shrivel up (Reece et al., 2014). However, it is quite different for plant cells. Plant cells require a hypotonic environment to stay turgid, so a isotonic causes the cell to become flaccid and a hypertonic results in a plasmolyzed cell (Reece et al., 2014). If a plant cell is plasmolyzed, the cell s plasma membrane has started to peel off of the cell wall, thus squeezing and bursting the organelles inside of the plasma membrane (Reece et al., 2014).

4 Different ph s can affect the cell the same way different tonicity levels do. The ph scale is a scale that measures how many hydrogen ions are in a (Reece et al., 2014). Solutions with a high concentration of hydrogen ions have lower ph levels, and s with a low concentration of hydrogen ions have a higher ph level (Reece et al., 2014). This is a key concept to understand when discussing the similarities of tonicity and ph and their effect on cells of living organisms (Reece et al., 2014). Tonicity and ph levels affect a variety of plants and other organisms differently. For instance, sweet potatoes, also known as Ipomoea batatas, use starch as a storage compound. The normal ph for a sweet potato cell is about 5.4 to 7.0 (Tawo, Abara, Malu, & Alobi, 2009). Anything other than a 5.4 ph may have an effect on the growth of a sweet potato because of the change it causes to the cells environment. There have not been many studies done on the impact of different ph s on vegetables or fruits, especially on sweet potatoes. One of the few experiments done to view the effect of ph levels on sweet potatoes was done by Lla ava, Asher, and Blamey (1995). These three scientists researched the effect of the ph of soil on the growth of sweet potatoes to aid farmers who grow them (Lla'ava, Asher, & Blamey, 1995). They found that the optimal ph for root and top growth varied from 4.5 to 7.0, but as the ph increased, there was a decrease in the concentration of nutrients (Lla'ava, Asher, & Blamey, 1995). Overall, this experiment focused on the agricultural side of sweet potatoes and ph levels and demonstrates how important diffusion is in living organisms. This particular experiment focused on the affect that ph had on a sweet potato core s weight. My hypothesis is if a sweet potato core is placed in a of a ph level higher than 5.4, the core will lose weight, and if a sweet potato core is placed in a of a ph level

5 lower than 5.4, the core will gain weight. My null hypothesis is that there will be no difference between the weight of sweet potato cores placed in different ph s. Methods: 1. Core five sweet potato pieces. 2. Label five beakers A through E and fill the beakers with the designated ph. Beaker A Beaker B Beaker C Beaker D Beaker E 100 ml of ph ml of ph ml of ph ml of ph ml of ph Label five weigh boats A through E and zero the electronic balance with a weigh boat on it. 4. Weigh the five sweet potato cores in weigh boats and record the initial weights. 5. Place the five cores in their designated beaker for ten minutes. 6. Pull the sweet potato cores out of the beakers using test tube holders and place them in their designated weigh boats. Make sure to shake the core off before placing in the weigh boat. 7. Weigh each potato core in the weigh boat and record the weight. 8. Repeat steps 5 through 7 until the sweet potato cores have soaked for 60 minutes in total. Results: After performing the experiment for 60 minutes, I found that the general trend for all five ph s was the sweet potato cores gained weight (Bauer & Norman, 2017).

6 As shown in the graph above, the sweet potato cores increased in weight by almost 1 gram in the first ten minutes of soaking, then began to stabilize or fluctuate in weight from the ten minute mark to the forty minute mark. After the first forty minutes, the sweet potato core consistently gained weight of a little under 0.5 grams. The average range of weight is 1.1 grams with the lowest being a difference of 0.21 grams for ph 7 and the highest being a difference of 1.54 grams for ph 2 (Bauer & Norman, 2017). Conclusion: Based off of the results, I can conclude that the data does not support my hypothesis. I predicted that the sweet potato cores would lose weight in a ph higher than 5.4 and would gain weight in a ph lower than 5.4. The data does not support the null hypothesis either due to the overall change of weight for all five sweet potato cores. Even though, all of the sweet potato

7 cores gained weight, it can be seen in the ranges of ph 2 and 7 that the ph 7 had the least effect on the core by only gaining a weight of 0.21 grams, while the ph 2 had the most effect on the core by gaining 1.54 grams. There was one large error that could have massively affected the experiment. The vegetable I thought was a sweet potato was actually a yam. Although yams and sweet potatoes are very similar, the normal ph for a yam is 6.0 to 8.0 and the normal ph for a sweet potato is 5.6 to 7.0 (Tawo, Abara, Malu, & Alobi, 2009). This could have severally changed the outcome of the experiment due to the differing ph levels that is considered normal. This is one of the only mistakes my team and I made during the experiment, so this is the only contributing factor that could have drastically altered the results. In the future, I would love to repeat this experiment using an actual sweet potato, and I would love to try a similar experiment with a yam to see what should have happened in this experiment. I would also like to study the effect temperature has on yams and sweet potatoes. Overall, the data does not support my hypothesis or null hypothesis. The results are very unclear on what they mean due to the fatal error of using a yam instead of the intended sweet potato. I would love to retry this experiment without the major error and, during the retry, I would do the experiment for a longer period of time to get more clear results.

8 References Bauer, N. & Norman, C. (2017). General biology III laboratory manual (3rd ed.). Plymouth, MI: Macmillan Learning Curriculum Solutions. Lla'ava, V. P., Asher, C. J., & Blamey, F. P. (1995). Plant-Soil Interactions at Low ph: Principles and Management. In Plant-Soil Interactions at Low ph: Principles and Management (Vol. 64, pp ). Springer Netherlands. doi: / _99 Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., Jackson, R., & Campbell, N. A. (2014). Campbell biology, volume 1: Custom edition for College of Western Idaho (Vol. 1). Boston, MA: Pearson Learning Solutions. Tawo, E.N., Abara, A.E., Malu, S.P., & Alobi, N.O. (2009). Evaluation of ph Levels in Some Common Carbohydrate Food Items Consumed by Communities in the Central Senatorial District of Cross River State, South-South of Nigeria. Pakistan Journal of Nutrition, 8: doi: /pjn