Abstract

The paper outlines an experiment conducted to test the effect of sodium bicarbonate on the level of photosynthesis in aquatic plants. A control experiment of water solution was used to monitor changes in the level of oxygen generated following different concentrations of NaHCO3. The results of the experiment point to a relationship between the two variables. Indeed, an increase in the concentration of NaHCO3 results to an increase in the volume of oxygen generated. However, increase of sodium bicarbonate beyond the optimal level of 1% results in reduced photosynthesis.

Introduction

This experiment aims to ascertain the effect of carbon dioxide availability on the rate of photosynthesis in plants.  The plant used in this experiment, Eloda densa, is well adapted to the aquatic environment and produces oxygen through the process of photosynthesis. The process of photosynthesis occurs in the presence of water, carbon dioxide as well as solar energy. The plant selected is quite interesting as it thrives under water despite the documented absence of enough solar energy in aquatic environments. In conducting the test, the addition of NaHCO3 was tested for its impact on the level of photosynthesis as it provided carbonic acid to the medium. Normally, HCO3 is more abundant in aquatic environments compared to carbon dioxide (Miao et al, 2011). Consequently, most aquatic plants have developed modifications to use HCO3 as a substitute of the limited carbon dioxide. Studies in the past have shown that aquatic plants use HCO3 in its original form and do not even convert it to carbon dioxide in the process of photosynthesis.

The experiment generated its hypothesis as thus: addition of more concentrations of NaHCO3 results in higher oxygen gas generation as a product of photosynthesis. The reasoning is that NaHCO3 is a source of HCO3, a product that is used in photosynthesis by aquatic plants such as the one in the experiment. In testing the hypothesis, the amount of oxygen generated was used as the independent variable. The gas does not mix with water and would thus float at the top of the inverted conical flask. The concentration of NaHCO3 in the solution was varied to become the dependent variable. The plant Elodea densa was then submerged into the different solutions and light emitted providing the conditions necessary for photosynthesis. The volume of oxygen was calculated at intervals of five minutes. The experiment predicted as thus: if more concentrations of NaHCO3 were added to the solution, then the more photosynthesis would occur and the more oxygen gas would be produced.

Materials and Methods

The experiment used a 250ml Erlenmeyer flask and various concentrations of sodium bicarbonate. In addition, healthy aquatic plants were used as well as a white light bulb for provision of required energy. Water solution was used as a control experiment. After the experimental set up was done then plants were dipped in the different concentrations of NaCO3 solutions in the presence of light from the white bulb. The lamps were placed approximately 15cm from the set up with each Erlenmeyer flask containing a plant having a test-tube. After the set up was completed, it was left to equilibrate for about ten minutes before readings were taken (BIOA02 lab manual, 2016). After the time had elapsed, observations of bubbles in the solutions were observed as well as the level of the solution in the pipette. The pipette was then reset to zero and readings on the pipette recorded after every five minutes. In analyzing the data, Microsoft Excel software was used in creating graphs.

Results

The results of the experiment are written as records of the volume of oxygen generated in different concentrations of NaHCO3. In all the experiments, the volume of oxygen generated was more when sodium bicarbonate was added compared to the volume generated in water. For instance, a concentration of 2.5% NaHCO3 had a volume of 0.55 ml in both tubes compared to the 0.20 ml volume generated in water. The critical t-value was constant in all the five tests at 2.145 as well as the df value at 14 (See table 1). However, the calculated t-values were not similar with test 5 generating the highest at 8.648851.

Table 1: t-test values

Similarly, the actual p-values were different as shown in the table. In addition, the amount of oxygen is highest at a NaCO3 concentration of 1% at a total of 1.6 ml in the two tests. The lowest volume of oxygen generation is recorded at a total of 0.4 for water solution (See figure 1).

Figure 1: total oxygen generation

Discussion

The results of the experiment show a relationship between the addition of sodium bicarbonate in water and the increase in photosynthesis. As thus, the hypothesis is accepted as there is considerable increase in oxygen generation when NaHCO3 is added into the solution. All the tests done under different concentrations accepted the hypothesis. In addition, the values from the t-tests including the critical t-value and the p-values (See table 1). Still, the results showed that the effect of NahCO3 on photosynthesis was significant (P<0.05). However, the optimal concentration of NaHCO3 was identified as 1% since it resulted in the highest volume of oxygen generated. The trend shows an increase in the level of photosynthesis as sodium bicarbonate concentration is increased (Ma et al, 2013). Upon attainment of the optimal concentration, further increase in sodium bicarbonate levels result in reduced photosynthesis.

The results of this study are consistent with past studies in the same field (Denison, 2012). All photosynthetic plants require carbon dioxide to facilitate the process of photosynthesis. In aquatic plants, the mechanism is modified to use HCO3 in place of carbon dioxide. The addition of sodium bicarbonate solution in the water acts as a source of HCO3 that is used in the process (Fageria & Moreira, 2011). Although the control experiment did not have an addition of NaHCO3, the plant managed to produce oxygen through the modified mechanism. However, an increase in the concentration of NaHCO3 resulted in increased photosynthesis characterized by higher levels of oxygen (Williamson, 2004). Ideally, an increase in the supply of HCO3 results in higher levels of photosynthesis in aquatic plants. However, the supply has an optimal point after which any addition may result in negative effects on the photosynthesis (Mattupalli et al, 2013). Any concentration after the optimal point of 1% resulted in slower photosynthesis and oxygen generation.

References

Ma Q, Scanlan C, Bell R, Brennan R. 2013. The dynamics of potassium uptake and use, leaf gas exchange and root growth throughout plant phenological development and its effects on see yield in wheat (Triticum aestivum) on a low-K sandy soil. Plant Soil 373:373-384.

Miao Y, Stewart BA, Zhang F. 2011. Long-term experiments for sustainable nutrient management in China. A review. Agronomy for Sustainable Development 31:397-414.

Denison RF. 2012. Selfish genes, sophisticated plants, and haphazard ecosystems. In Darwinian Agriculture: How Understanding Evolution can Improve Agriculture. Princeton (NJ): Princeton University Press. Pages 76-94.

Fageria NK, Moreira A. 2011. The role of mineral nutrition on root growth of crop plants. Advances in Agronomy (Book series) 110:251-331.

Williamson RC. 2004. Deciduous tree galls [Internet]. Madison (WI): University of Wisconsin-Madison; [cited 2016 October 27]. Available from http://labs.russell.wisc.edu/pddc/files/Fact_Sheets/FC_PDF/Deciduous_Tree_Galls.pdf

Mattupalli C, Genger RK, Charkowski AO. 2013. Evaluating incidence of Helminthosporium solani and Colletotrichum coccodes on asymptomatic organic potatoes and screening potato lines for resistance to silver scurf. Am J Potato Res [Internet]. [Cited 27 October 2016.] Available from http://link.springer.com/content/pdf/10.1007%2Fs12230-013-9314-3.pdf

 
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