Effect of pH Levels on the Growth of Bean Plants

Custom Student Mr. Teacher ENG 1001-04 29 July 2016

Effect of pH Levels on the Growth of Bean Plants

Different pH level may affect the growth and development of the plants. Certain key words include: pH level, germination, acidity, osmosis and diffusion. This experiment examines the effects of different pH level of vinegar on the growth of bean plants. Materials used in this experiment consist of: water (pH 6), vinegar with the pH level of 3, 4 and 5 (each one were made before experiment), beans, soil, and pots. Eight bean plants were planted, two were watered with pH 6 and the other ones were each watered with pH 5, pH 4 and pH 3 vinegar. The results were that beans watered with pH 3 shrunk and began to die, pH 4 beans were growing at a slow rate, beans watered with pH 5 grew at a fairly normal pace and pH 6 grew the fastest. Overall, the more acidic the environment, the harder it is for plants to survive.


Acidity is the quality or state of being acid; pH below 7. Exploring the different levels of acidity affect plant growth and development, the process of germination must occur to see the affects upon the growth of the beans. Germination is the process whereby seeds or spores sprout and begin to grow. With the acidity expressed with pH levels is the measure of acidity or alkalinity of a solution, in depth the measure of the activity of dissolved hydrogen ions (H+). Following these concepts is the process of “normal” plant growth. Plants require nutrients for growth. Their process depends on the essential nutrients of abundant sunlight, water, fertile soil, and minerals6. To investigate how the plants respond to changes in the acidity of their environments, photosynthesis is another significant concept involved. Photosynthesis is the a process by which energy from the sun is trapped by chlorophyll and is later converted to chemical energy with the key reactants of water, carbon dioxide and light6.

Osmosis is the diffusion of water in which the plants obtain their water and nutrients from3. Replacing water with acids of different pH levels (1 being most acidic and 12 the most basic) it is hypothesized that the lower the pH of the acid used to water the plant the faster and more fatal for the plant undergoing plasmolysis (when the plant cells diffuse water out to establish equilibrium in its environment) to perish. The plants watered with a lower pH solution either as stated dies or grows at a slower rate that the controlled plants of pH 6. The conclusion of this hypothesis was based off the knowledge provide from the media about the effects of not only global warming but also acid precipitation and their harms. The process of this experiment was to simulate the actual acid precipitation of nitric and sulfuric acids in which was represented with vinegar solutions to observe the plant responses to different environmental conditions .

Materials and Equipment

•Eight bean plants•One medium sized pot (about 10-15 cm in diameter)•4 small pots (about 5-7 cm in diameter)•A pack of wide-ranged pH paper (is able to detect pH levels of 0-12)•About 500 mL of white vinegar•Three 500 mL beakers•Tap water•A planting area with plenty of light•Planting soil mix•Tape and a marker to label the pots•A rulerMethodsRefer to Figure 1 for the following set-up. The pots were filled with a planting soil mix and one bean was planted into each of the small pots by pushing the beans about 2.5 cm into the soil and covering the hole with soil. Two beans were planted in the medium sized pot with the same methods. Beans were embedded near the centre of the pot to allow room for the roots to extend and the beans that shared a pot were planted near the centre, about 2 cm apart.

Figure 1: Experimental Set UpFigure 1 shows the experimental set up for this investigation (the distance of the seeds from the soil’s surface and the distance between seeds sharing a pot.

The pots were placed in an area with lots of light (under lamps) and were watered with tap water until the beans germinated and grew to about 5cm. The beans germinated at different times and thus the plants were different height when the independent variables (the pH of the solution they were watered with) were added.

While the plants were germinating and growing, an observation table based on Figure 2 was created to record the following variables:Date, pH, height, colour, shape, and other information.

Figure 2: Observation Table templateFigure 2 shows the template for an observation table needed to record data collected from this investigation.

The height, colour and shape were variables that depended on the pH (the independent variable), and so by manipulating the pH level, the dependent variables were also manipulated. Solutions with different pH solutions were created in order to manipulate the independent variable. Refer to Table 1 for the ratios needed to create the pH solutions. Note that because tap water’s pH may be different depending on the water supply, it is best to follow Table 1, and test the pH using pH paper. If the pH level is correct, then add more water or acid accordingly.

Table 1: Ratios needed for pH solutionspHVolume of Tap WaterVolume of VinegarpH 3None250 mLpH 4500 mL50 mLpH 5500 mL5 mLpH 6500 mLNoneTable 1 shows the volumes of tap water and vinegar needed to make the pH solutions.

When the plants grew to the appropriate height, each pot was labelled with the pH level which they would be watered with. Two of the small plats in the small pots would be watered with a pH 3 solution, and so those pots were labelled as “pH 3”. Two “pH 3” plants were needed because it produced a result that was extremely different from the other plants, and so the result needed to be confirmed.

The plants in the remaining small pots were labelled “pH 4” and “pH5”. The medium sized pot was labelled “Control”, as it would be watered with tap water rather than a diluted acid. The control plants helped emphasize the changes manipulations to the independent variable (the pH level) caused in the dependent variable (the height). Again, two plants were needed for the control in order to confirm the results.

After labelling was completed, the data listed in Figure 2 was recorded in the observation table. The height was measured using a ruler. Watering began after the first set of data was recorded. Each plant was watered with the pH solution indicated by their labels. There should be just enough solution to wet the immediate area around the stem of the plant.

The plants were watered once (each) every two of three days, and data was recorded each time the plants were watered. Watering continued for two weeks until 8 sets of data were recorded (data for 8 days).

Observations and Results

All of the plants except for those watered with a pH 3 solution grew at different rates, resulting from the differences in the pH levels of the solutions used to water the plants. The ‘controlled plants’ (plants watered with tap water) grew much faster than most of the other plants. This represented the growth rate of plants in a ‘normal’ environment in which the independent variable (the pH level of water) has not been manipulated. By comparing the other plants with the controlled plants, a better conclusion can be reached. The growth rate of the other plants can be compared with the growth rate of either controlled plants reflected in Figure 3:Figure 3: The Growth Rate of pH 6 plant BFigure 3 shows the height of pH 6 plant B over the span of two weeks.

The controlled plant grew almost exponentially over the span of two weeks. As reflected in Figure 3, Plant B have a slower growth rate near the beginning of the investigation, and towards the middle and near the end, the plant experienced very fast growth. Because this plant was watered with a “controlled” material (tap water), it is seen as the normal growth of a bean plant.

It was hypothesized that the plants watered with a lower pH solution would either die before the other plants would, or would grow much slower than the other plants. As reflected in Table 2, the plants watered with the pH 3 solution began dying within 2 days, while the other plants remained alive.

Although the other plants remained alive for the duration other the investigation, the rate of growth still differed from plant to plant. For example, when the investigation began, the pH 5 plant and the pH 4 plant were the same height (refer to Table 2). However, as watering with acids began, the pH 5 plant continued to grow, but the pH 4 plant would remain the same (or around the same) height for almost the entire investigation, and only grew a total of 2 cm at the end of the investigation. The different between the pH 4 and the pH 5 plants are shown in Figure 4:Figure 4: Comparison of the growth rates of the pH 5 plant and the pH 4 plantFigure 4 shows the height of each plant for each day recorded.

Discussion part 1The hypothesis was correct, that the beans watered with the more acidic vinegar died faster. During the process, the bean that was water with pH 3 slowly shrunk and shrivelled up. However, the bean that was water with pH 6 never shrunk or shrivelled, instead it grew the fastest and healthiest. Refer to Table 2, the pattern shown was that the more acidic the solution is, the less likely the plants will survive in that environment. The independent variable (pH levelled solutions) affected the dependent variable (the plants, in this case the beans) as predicted. Due to the low pH level, the beans watered with it gradually shrunk and dried up. In comparison, the beans watered with the higher pH level (pH 6), grew tall and healthy looking. In the end, the independent variable, the pH level affected the growth of the dependent variable, the beans as expected.

Discussion part 2The data gathered shows the effect of acid on bean plants. It was hypothesized that the plants watered with an acidic solution would grow slower than the control plant because acid can denature proteins and cause damage to cells and tissue . As hypothesized, the plants watered with a lower pH solution either died very quickly or grew at a much slower rate than the controlled plant. As reflected in the data recorded on the final day of the investigation (Table 2), the closer to neutral the solution the plants were watered with, the taller and faster they grew (as reflected in Figure 5):Discussion part 3Although, the results of the plants in acidity conditions were accurately hypothesized, experimental error may have occurred. Meaning if any experimental errors occurred they have not impacted the results.

However, in the process of germination of the bean plants several setbacks aroused. For instance, watering the seeds in the pot may have been too heavy and may have leeched the seed further down the pot causing its death. Other times were where outside interferences may have removed the germinated plants from its pot. Looking at the main procedures of this experiment the lack of supervision of the acids made have weakened or strengthen their pH as outside elements were exposed to them when the parafilms has ripped or ruptured. This changes the effect of soil pH which is great on the solubility of minerals or nutrients. As fourteen of the seventeen essential plant nutrients are obtained from the soil5. Some plants if shared a pot is another factor that may have affected the results a little as competition for nutrients occurred. Other incidences like providing abundant sunlight to the plants, as the sunlight was mimicked by fluorescent light the plants at the ends may have obtained less light for their process of photosynthesis. Procedural errors may have impacted the results more than instrumental errors; however it was not adequate enough to obtain false results as proven in figure 5.

As the purpose of this lab was to simulate actual acid precipitation it relates greatly to the society, economy and the environment. The result of this experiment proves to be a direct impact on the environment as it can ruin or kill off plant vegetation. Starting off from the industries (economy) that pollute the atmosphere with emissions of air pollutants like carbon monoxide, nitrogen dioxide and sulfur dioxide that also seriously affect the health in children, the elderly, and people with heart and lung conditions4. It contributes the formation of acid rain which in this case is the objective of the experiment.

Our mimics of acid precipitation affect ponds, lakes, and streams that lead to not only the disappearance of vegetation but animal life too. In one case, the sulfuric acid plant discovered to have cost a total of two million dollars charged on DuPont and Lucite International Inc. to the United States and the state of West Virginia on April 2009. Not only have the chemical manufacturing complex made modifications to their plant in 1996 without first obtaining pre-construction permits and installing required pollution control equipment their plant emits 98.7 tons of sulfuric acid mist, 86.1 tons of nitrogen dioxide and 212.4 tons of carbon monoxide that contributes to smog each year4. This experiment provided direct importance to the responds of emissions and pollution even thought it was only the use of vinegar.

Figure 5: Comparison of the ‘Final Height” of Each plantFigure 5 shows the height of each plant on the final day of the investigation (May 1st, 2009).

Acid likely affects the plants’ health and growth because they could create environments which make denature proteins in the plants. As plants absorb water and nutrients from their roots, protein in plant cells could be exposed to low pH levels. Also, because acids are solutions, they could put the plants in a hypertonic environment in which there are more solutes outside of the cell than solvents.

Plant cells undergo osmosis (the diffusion of water) in order to obtain water and nutrients. Osmosis usually occurs down a concentration gradient, meaning that the cell would try to establish homeostasis by diffusing water in or out of the cell to equalize the concentration of each environment. Because there are solutes in the acids used to water the plants, it lowers the concentration of water in the soil. To try and establish homeostasis, the cells would diffuse water out. This environment would cause not only the plant to retain less water than a plant that has been watered with tap water, but it would cause the plant to lose water, causing plasmolysis (in which the cells shrivel).

As seen in Figure 5, there are still some inconsistencies in the correlation between plant height and acidity. For example, although Plant A was more neutral than pH 5 Plant, it is shorter. This is a result of several factors: Plant A had germinated later than pH 5, and so would be ‘lagging’ behind in terms of growth, and Plant A also shared a pot with Plant B, which may have competed with Plant A for nutrients and growth room for roots. Although the beans were planted a fair distance apart, roots can grow past that distance.

Another inconsistency is that, although acidity level (the number of hydrogen ions released in solution) increase or decrease tenfold per pH level, some levels have growth patterns that are more alike than others, despite the pH difference of only one. For example, the plant watered with a pH 5 solution has experienced 10 times more acidity (10 times more hydrogen ions) than the larger controlled plant (which germinated at around the same time as the pH 5 plant). Despite this, the plants grew at a similar pace, and the difference in their final height is small, as reflected in Figure 6 and Table 2.

Figure 6: Comparison of the growth rate of Control Plant B and pH 5 PlantFigure 6 shows the height of each respective plant on the days recorded.

pH levels further from neutral have a wider range of effects on the plant, however. The ratio of hydrogen ions in the acid watering the pH 4 Plant and the pH 3 Plants were the same was the ratio between the controlled plant (B) and the pH 5 Plant, but the different in health and growth of the pH 4 Plant and the pH 3 Plants were drastically different, as reflected in Table 2. Although the pH 4 Plant grew much slower than the control plant (B) and the pH 5 Plant, it still remained alive and fairly healthy (as reflected in the “Shape” and “Colour” columns of Table 2). The pH 3 Plants, on the other hand, died or began to die only two days after it was watered with pH 3 acid. As reflected in the “Shape” and “Colour” columns of Table 2, while the pH 4 Plant maintained its healthy colour and shape, both pH 3 Plants became very shrivelled and the colour became very unsaturated.

These results could be explained by experimental error. The pH solutions used to water the plants were unsupervised, and although parafilms were used, they often broke, allowing outside elements to fall into the solution. This could change to pH level of the acids. The solutions were not tested for their acidity aside from the initial preparation for the investigation. This could mean that the pH 5 solution had become less acidic than before, or the pH 3 solution had become more acidic than before.

Moreover, acids affect different plants differently . Although all of the plants were of the same species, they could still possess alleles that make them slightly unique from each other. It is possible that these alleles could affect how acid affects the plants’ growth.

Rubin, Ken. “Effect of Acid Rain on Plants.” SOEST| School of Ocean and Earth Science and Technology. School of Ocean and Earth Science and Technology. 13 May 2009 .

Rubin, Ken. “Effect of Acid Rain on Plants.” SOEST| School of Ocean and Earth
Science and Technology. School of Ocean and Earth Science and Technology. 13 May 2009 .

³ Galbraith, Donald, Leesa Blake, Jean Bullard, Anita Chetty, and Eric Grace. McGraw-Hill Ryerson Biology 11. Toronto: McGraw-Hill Ryerson Limited, 2001. Print.

4 “Sulfuric Acid Plant Emissions Cost Dupont and Lucite $2 Million.” Environment News Service 20 Apr 2009 Web.14 May 2009. .

5 “Soil pH: What it Means.” SUNY-ESF E-Center. 2009. State University of New York College of Environmental Science and Forestry. 14 May 2009 .

6 Paillai, Maya. “Plant Growth Process: How does a Plant Grow?.” Buzzle.com. 17 June 2008. 14 May 2009 .


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  • University/College: University of Arkansas System

  • Type of paper: Thesis/Dissertation Chapter

  • Date: 29 July 2016

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