Effect of Carbon Dioxide Availability on the Photosynthesis Rate of an Aquatic Plant

Subject: Science
Type: Proposal Essay
Pages: 6
Word count: 1537
Topics: Biology, Microbiology, Photosynthesis
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The process of photosynthesis is an important activity for all organisms; the process can be affected by a variety of factors that influence both the heterotrophic and autotrophic organism. The purpose of this research was to determine how carbon dioxide concentration can affect the rate of photosynthesis by using the scientific method. In the experiment, it was hypothesized that an increment in carbon dioxide concentration would definitely increase photosynthesis activity. This hypothesis was proven correct when the various concentration of bicarbonate solution increases the rate of photosynthesis. Thus, it can be concluded that various concentration of carbon sources can affect the photosynthesis and that an increment in the concentration of carbon source would increase the rate of the photosynthesis process.

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Effect of Carbon Dioxide Availability on the Photosynthesis Rate of an Aquatic Plant

Photosynthesis is the process in which autotrophic organisms synthesize organic molecules such as sugars from an inorganic salt, carbon dioxide, and water. The photosynthetic rate is affected by several factors, including the availability of carbon dioxide, temperature, light intensity, and availability of water. The concentration of carbon dioxide will directly affect the rate of photosynthetic plants as it is directly used in the photosynthesis reactions (C. Baligar, V. 2012).  Thus, improving the condition of autotrophic plants would directly lead to an increase in the rate of photosynthesis.  According to Xu, C., Zhang, J., Mihai, D., & Washington, I. (2013), the photosynthetic plants contain light-sensitive pigments known as chlorophyll which capture energy. These cells are then able to convert energy into organic molecules in the presence of carbon dioxide. The cells do not only drive Calvin cycle, but also produces most of the oxygen available in the atmosphere. Consequently, heterotrophy plants use photosynthetic products to break down sugar and release carbon dioxide (Bruhn, Mikkelsen & Atkin, 2002).  The main purpose of this research was to test whether the availability of carbon dioxide would affect the process and the rate of photosynthesis in the aquatic plant by using the scientific method. In this method, we will use oxygen production as an indicator of the photosynthesis process. The photosynthesis activity uses carbon dioxide as a reactant and then release oxygen as a by-product. We will measure the rate of photosynthesis of aquatic leaves in a solution saturated with bicarbonate which serves as the source of carbon. We hypothesized that an increase in the concentration of carbon source would directly increase the rate of photosynthesis until it is saturated as measured by the number of oxygen bubbles produced.  Thus, it is essential to note that the presence of carbon source does affect the rate of photosynthesis because carbon dioxide plays an important role in photosynthesis processes (Ziska, Sicher & Bunce, 1999).

Materials and Methods

Apparatus needed for the experiment

In order to succeed in conducting this experiment, specific materials and methods we required. Materials essential in this experiment includes 250 ml Erlenmeyer flask, sodium bicarbonate of 0.7% concentration, regular tap water, 4 healthy aquatic plants, plastic container to store plants, desk light with white light bulb, rubber stopper with 1ml pipette and 10 ml syringe with needle, 75 ml glass tube, and scissors and forceps. In addition, all laboratory rules and safety precautions should be followed throughout this experiment.

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The rate of photosynthesis in aquatic plants was subjected to bicarbonate solution as the source of carbon and the number of bubbles produced in the form of oxygen was measured. The following procedure was used in the experiment.

  1. The apparatus was set up by obtaining two 250 ml Erlenmeyer flasks and two clean 75 ml glass tubes. The tubes were marked as tube 1 and the other as tube 2, and they were used as miniature photosynthesis chambers, and 225 ml of regular tap water was poured into the two 250 ml Erlenmeyer flask.
  2. Both tube 1 and 2 were filled with 75 ml of bicarbonate solution, and they were carefully placed into one of the 25 ml Erlenmeyer flask containing tap water; these tap water in Erlenmeyer flask acted as a temperate controller during the process of experiment.
  3. The aquatic plant of approximately 20 cm longs with healthy leaves was mounted on a working stand. The plant was cut to 15 cm from the growing tip by using scissors; it was cut under water to avoid exposing the cut tip to the air to prevent airlock and gaseous flow during the whole process of experiment.
  4. 1 plant was placed in each of test tube 1 and 2 and care were taken to ensure that the growing tips of the plants were placed at the bottom of the tubes and the cut tip at the top. The plant was entirely submerged in the bicarbonate solution filled in tube 1 and 2.
  5. The stem of the plant was kept submerged in the solution; the scissor was inserted into tube 1 and cut off 0.5 cm of the stem. The cut was made on the internodes between the leaves instead of the nodes. It is important to ensure that the stem remained submerged in bicarbonate solution while cutting and it was not exposed to air as stated in step 3.
  6. Step 5 was repeated for the aquatic plant in tube 2.
  7. A rubber stopper attached to the bent pipette, needle, and syringe was then placed in each of the tubes. It is advisable to ensure that no air is trapped in the test tube when placing the stoppers. The bicarbonate solution was left to overflow the tubes after adding the stopper, and the excess solution was wiped out with paper towels.
  8. Finally, the stopper was gently pushed into each of the tubes to ensuring that no air bubble was available in the tubes. The solution was moved into the bent pipette and fully inserted stopper, the needle-syringe was used to remove the solution from the tubes to allow the level of the solution in the bent pipette to be 0 or in a suitable starting point close to the bend in the pipette.


The effects of bicarbonate as carbon source continued to increase the number of oxygen bubbles in the stem with an increase in the concentration of NAHCO2 in 5 test tubes as shown in table 1 below. Thus, carbon dioxide is a necessity for the photosynthesis process. It is useful in making the organic products of photosynthesis. If the aquatic plant is able to absorb more carbon dioxide, then the rate of the photosynthetic process will definitely increase as the plant are able to make more organic components; thereby rejecting the null hypothesis of the experiment. Thus, the aquatic plant is given carbon dioxide in the form of sodium bicarbonate.

Table 1: Data from the experiment using various concentration of NAHCO2 in 5 test tubes to analyze the rate of photosynthesis in an aquatic plant

  TEST 1 – total ml TEST 2- total ml TEST 3-total ml TEST 4- total ml TEST 5- total ml
Treatment Control (H2O) 0.1% of NAHCO2 Control (H2O) 0.3% of NAHCO2 Control (H2O) 0.5% of NAHCO2 Control (H2O) 0.7% of NAHCO2 Control (H2O) 1% of NAHCO2
Sample (n) 8 8 8 8 8 8 8 8 8 8
critical t– value 2.145 2.145 2.145 2.145 2.145
calculated t-value 2.3928 7.7684 7.5614 6.9812 12.7338
df 14 14 14 14 14
actual p-value 0.0313 0.0001 0.0001 0.0001 0.0001
Conclusion (did you reject or fail to reject the null hypothesis?)   Reject Reject Reject Reject


Based on our results, the questions and hypothesis that an increase in the source of carbon (bicarbonate) concentration would definitely increase photosynthesis were correct. The results showed that a higher concentration of bicarbonate increased the rate of photosynthesis. Our concentration of 0.1% bicarbonate showed that without carbon source no any process of photosynthesis could occur. In our other concentration of 0.3, 0.5, 0.7, and 1.0, it showed that the process of photosynthesis occurs with an increase in the concentration of bicarbonate; thus, rejecting the null hypothesis of the experiment. The aquatic plant absorbed more carbon dioxide and produced oxygen which in turn increased the pressure in stopper and syringe; thereby pushing the air bubbles down. The plant, in turn, produces oxygen as an end product during the process of photosynthesis. Nevertheless, an increase in the rate of bicarbonate of above certain levels would have no effect on the process of photosynthesis because other factors such as light would be limiting the reactions.

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In conclusion, we attained our aim of discovering the effect of various carbon dioxide concentrations on photosynthesis rate. As shown in the data, we noted that an increase in the concentration of carbon dioxide caused an increase in the photosynthesis rate. Re-conducting this research would need extra precaution to ensure that no leaves are damaged and corrected made solutions are available for true results. In addition, extra trails in the experiment would be required to eliminate any form of outlier information. In conclusion, the rate of photosynthesis in the aquatic plant could also be affected by light intensity, color, and pressure. All these are potential variables that could be used for future research.

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  1. Bruhn, D., Mikkelsen, T., & Atkin, O. (2002). Does the direct effect of atmospheric CO2 concentration on leaf respiration vary with temperature? Responses in two species of Plantago that differ in relative growth rate. Physiologia Plantarum114(1), 57-64.
  2. Baligar, V. (2012). Photosynthetic Photon Flux Density, Carbon Dioxide Concentration and Temperature Influence Photosynthesis in Crotalaria Species. The Open Plant Science Journal6(1), 1-7.
  3. Xu, C., Zhang, J., Mihai, D., & Washington, I. (2013). Light-harvesting chlorophyll pigments enable mammalian mitochondria to capture the photonic energy and produce ATP. Journal Of Cell Science127(2), 388-399.
  4. Ziska, L., Sicher, R., & Bunce, J. (1999). The impact of elevated carbon dioxide on the growth and gas exchange of three C4 species differing in CO2 leak rates. Physiologia Plantarum105(1), 74-80.
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