The effects of pH on mung beans
Gloria Cheng
Winsy Cheung
Lily Wong
Christine Yen
January 15, 1998
Abstract
This experiment explores how different pH environments affect the growth of mung beans. The mung beans were grown in water with various pH levels, consisted of pH levels 5, 6, 7, 8, and 9. A replicated design was used consisting of 3 runs for each pH level. The following results are listed in order of pH levels allowing most growth to least growth of the mung beans: 7, 8, 6, 5, and 9. These results show that pH 7 allows the most growth. Also, pH 7 happens to be the pH level of water.
Introduction
For the growth of all plants, specific levels of pH in the soil and in the plants themselves are important. These levels of pH affect the growth of the plants. In many cases, it is best for plants to have an acidity somewhere between pH 6.0 to pH 7.5 [1]. Plants cannot grow without nutrients. When the plants are placed in an acidic environment, there is not enough nutrients for the plants because hydrogen ions remove the other positively charged ions from the environments where the plants are in. These mineral ions, which the plants need, leach out of the soil [2]. So, when a plant is planted in extremely acidic soil, the plant does not have enough nutrients to grow. If the soil pH is too high, the iron in soil precipitates out. The nutrients that the plants obtain are determined by the acidity of the soil. However, in this study, the pH level for optimal growth of mung beans was never included.
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This experiment was chosen because one of our group members has a garden in her backyard. Her family would like to grow vegetables and other plants there. They want to know what pH solution is best suited for the growth of mung beans. They also want to know whether the pH level in their soil is suitable for the growth of mung beans.
The purpose of this experiment was to find out how the pH affects the growth of mung beans. We wanted to see which pH level(s) lead to the most growth and which pH level(s) hamper the growth of the mung beans. We chose to have a pH range of 5 to 9 in this experiment because any extreme pH levels would prevent the plants from growing.
Materials and Method
About 30 mung beans were first germinated on wet cotton pads in room temperature for three days. On the first day of the experiment (fourth day of beans’ germination), fifteen beans with the best growth were selected and transferred to two ice-cube trays, each with twelve cubicles, where a piece of cotton was place in each cubicle and watered with about 3 mL of water. This provided a humid environment for the beans. One bean was put into each cubicle. Then they were randomly assigned to water with different pH solutions: pH 5, 6, 7, 8, and 9, in which pH7 was used as a control since it was close to the pH level of water. The buffer solutions for the desired pH levels were mixed using citric acid, boric acid and Na3PO4, and stored in five different Erlenmeyer flasks to use for the next several days. The trays were stored in a corner of a classroom counter. Initial lengths of the mung bean spouts were recorded before watering with 2 mL of buffer solutions. After adding the pH solutions through a small plastic pipette, each compartment was tested with a pH paper to ensure the proper acidity. On the second day, the length of each bean was recorded. A pH test using pH papers was again given before watering them with 0,5 mL of buffer solutions. The identical procedure was repeated for the third and fourth day of the experiment. The lengths of the bean spouts were recorded daily so that we could compare the effects of different pH solutions on the growth of mung beans.
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Results
The average growth rate of mung beans under different pH environments.
pH level Sample A Sample B Sample C Avg. growth of four samples (4 days)
pH 5 2 mm 5 mm 8 mm 5 mm ± 2.1
pH 6 4 mm Died 9 mm 6.5 mm ± 2.6
pH 7 13 mm 12 mm 11 mm 12 mm ± 2.1
pH 8 6.5 mm 14 mm 1.5 mm 7.3 mm ± 2.1
pH 9 5 mm 5 mm 2 mm 4.3 mm ± 2.1
In this four-day experiment, the lengths of the bean spouts were measured daily. The three samples of mung beans watered with pH 7 solution grew the most, with the average growth of 12 mm. The beans did not grow well in the two extreme pH levels, pH 5 and pH 9, with only growths of 5 mm and 4.3 mm, respectively. The variance for pH 5, 7, 8 and 9 is 2.1, and 2.6 for pH 6.
Discussion
From this experiment, it shows that the pH of the solution affects the growth of the mung beans. The data implies that mung beans seem to grow more under pH 7, which supports the theory. It stated that that the mung beans grow best in the range of pH 6 to pH 7.5. They grow slower in the extreme pH levels, probably because the chemicals in the basic and acid solutions prevent mung beans from taking enough water molecules, and they need these water molecules to grow. The other reason maybe because the chemicals in the extremely acidic (or basic) solutions cannot cross the plasma membrane of the mung beans cells easily, which retard mung beans’ growth.
The variance for all pH’s except pH 6 is 2.1, and 2.6 for pH 6. These values account for the possible errors happened during the experiment that might have affected the data. The variance value for pH 6 is higher than the other pH levels because one mung bean sample in pH 6 died. A smaller sample size in this pH level could result in a greater data variation.
It is possible that there were some errors in this experiment. The pipette might not have been rinsed thoroughly, which might have made the pH of the solution less accurate. The cotton pads might contain other chemicals that affect the growth of the mung beans. Furthermore, we neglected the effects of the possible chemicals from the mung beans. Also, since the sprouts of the beans were mostly curled, there might have been some mistakes when we measured them with a ruler. Also, these sprouts were short, which made them quite hard to measure.
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Follow-up experiments can be made to test the effects of pH levels on the plant’s growth. They are necessary because this experiment only tested mung beans that were placed in an environment with pH range of 5 to 9. If there are more varieties of pH levels, more generalizations can be obtained. Improvements are needed on these follow-up experiments. There should be more time for the plants to grow. The taller the plants are, the easier it is to measure. Also, it would be better if the mung beans are placed in soil instead of cotton pads because soil provides more nutrients for plants. Therefore, the effects of the pH solution will be more obvious since it is certain that some acid solution will leach the mineral ions out of the soil.
The results from this experiment lead to a new focus question: whether it is better for the mung beans to grow in a basic solution or in an acid solution. This experiment does not tell us any difference between an extreme acidic environment and an extreme basic environment.
Appendix
1. Variance for all pH levels except pH 6:
(32+02+32)/2 = 9 x 3 = 27 (2.52+2.52)/1 = 25/2 = 25
(12+02+12)/2 = 1x 3 = 3 (0.82+6.72+5.82)/2 = 39.585 x 3 = 118.755
(0.72+0.72+2.32)/2 = 3.135 x 3 = 9.405
1.83.16 ? 14
S2 = 13.1
S2/3 = 4.4
S = 2.1
Variance for pH 6:
S2/2 = 6.6 S = 2.6
References
[1] Donahue, Roy L. Our Soils and Their Management. Danville, Illinois: The Interstate Printers & Publishers, Inc., 1961; pg. 151.
[2] Arms, Karen. Biology: A Journey into Life, Third Edition. Orlando, Florida: Saunders Publishing Company, 1994; pg. 690-691.
© Winsy Cheung, Gloria, Cheng, Lily Wong, Christine Yen 1998
