The Rate of Photosynthesis in Two Submerged Organisms (Cabomba and Ceratophyllum)
Introduction
In this experiment, the set alternative hypothesis was that the rate of oxygen production in Cabomba was significantly different from the rate of oxygen production in Ceratophyllum. This was informed by the report from a previous study by Van and colleagues (1976) that indicated that Cabomba had a lower rate of photosynthesis compared to Ceratophyllum and Hydrilla that had similar photosynthetic rate.
Materials and Methods
Experimental Design
The experimental independent variables were 6 grams for Ceratophyllum and Cabomba organisms while oxygen produced was the dependent variable. Water collected from the pond was used as the control in the experiment. The question to be answered was whether there is any significant difference in the rate at which oxygen is produced by Ceratophyllum and Cabomba. The prediction for the study was that each plant had a different rate of oxygen production.
The treatments were divided into two treatment 1 and treatment 2. The experiments were conducted by different groups with each group working on two treatments and a control. Each treatment was conducted in duplicates. In treatment 1, the treatment involved 6 grams of Ceratophyllum that was then filled with the appropriate amount of pond water. In treatment 2, the treatment involved the introduction of 6 grams of Cabomba into the experimental tube which was then filled with the appropriate amount of pond water. Control tube contained only the appropriate pond water with no organism.
Experimental Apparatus
The Closed Manometric System
The apparatus that was used to measure the amount of oxygen produced in the experiment was the closed manometric system. The system had various components, which included a tank, test tube rank, three glass tubes, three stoppers assemblies, each with a stopper, syringe and pipette, plastic Pasteur pipette, blue water (fluid indicator), and conditioned water for glass tubes.
Organisms used in the Experiment
The experiment used two different kinds of organism. These organisms were Ceratophyllum and Cabomba. For each organism, six grams were weighed ensuring that the content of water present on the weigh scale was minimal.
Glass Tube Contents-Experimental and Control Tubes
For each treatment, there were three glass tubes. Two of the glass tubes acted as the experimental tubes and contained 6 grams of each of the two organisms. The other tube acted as the control tube with no organism. The control tube only had water with no organisms.
Closing the Manometer System
Each syringe plunger was set to about 2 units on each syringe. A stopper was used to stopper each glass tube on syringe assembly and a small drop of blue water (fluid indicator) was added to the end of each pipette using the plastic Pasteur pipette. The water droplet was pulled using the syringe into the main body of the pipette making sure that the droplet measured between 3mm and 5mm in length. Using the syringe water droplet was adjusted to a starting position. During this process, it was ensured that the each pipette was in a horizontal position.
Equilibration
After completing the setup, each of the systems was allowed to stand for 15 minutes in order to allow the organisms equilibrate to the variable. During the equilibration time, movement of the blue water (fluid indicator) in each pipette was observed taking place slowly away from the direction of the stopper. Incidents where there were no movement of a water droplet or water droplet moved in the opposite direction rechecking of the system was done making sure that the system had no leakage. Since the control tube had no organism, there was no movement that was expected in these tubes.
Measurement of Oxygen Produced
The closed manometer was used to measure the amount of oxygen produced by the organisms through photosynthesis process. The water droplet (fluid indicator) was reset using the syringe to a pre-determined value on the pipette in each of the systems. A timer was started and the readings on the pipette taken at an interval of two minutes. The reading was conducted from the same side of the water droplet. Any change in the water droplet position was as a result of the oxygen produced by the organisms. Time as which pipette reading was taken and the pipette readings were recorded in respective tables for the two organisms. The measurements were taken at an interval of 2 minutes for a period of 16 minutes. The recorded readings for each tube were added to the appropriate class data sheet. At the end of the experiment, all the experimental apparatus were taken back to their location and spilled water wiped. The working station was cleaned leaving it clean and dry.
Results
Treatment 1
The pipette readings indicated the cumulative amount of oxygen that was produced during photosynthesis. These measurements were recorded in the Ceratophyllum table (Table 1).
Photosynthetic Rate Calculations
The rate of photosynthesis for each experimental and control tube in treatment 1 was calculated using the gradients of the slopes obtained after plotting a graph of cumulative oxygen produced against time in hours (Figure 1). Drawing a line of best fit for all the graphs gave a line with a gradient that was taken to be the rate of oxygen production per hour. To determine the rate of oxygen production per hour per gram of an organism, the gradient of the slope was divided by the mass of the organism used.
The rate of photosynthesis for the organisms in the tube in group 1 was calculated as follows. The slope had a gradient of 0.1375mL oxygen produced per hour which was divided by the mass of the organisms (6.07 grams) used in the experimental tube.
rate of oxygen production=0.1375ml/hour6.07 g0.0226
For this tube, the rate of oxygen production was, therefore, 0.0226ml of oxygen produced per hour per gram of Ceratophyllum
The rate of photosynthesis for the organisms in tube 2 in group 1 was calculated as follows. The slope had a gradient of 0.3425mL oxygen produced per hour which was divided by the mass of the organisms (6.05 grams) used in the experimental tube.
rate of oxygen production=0.3425ml/hour6.05 g0.325
For this tube, the rate of oxygen production was, therefore, 0.325ml of oxygen produced per hour per gram of Ceratophyllum
The rate of photosynthesis for the organisms in control tube in group 1 was calculated as follows. The slope had a gradient of 0.0625mL oxygen produced per hour.
The rate of photosynthesis for the organisms in tube 1, in group 2, was calculated as follows. The slope had a gradient of 0.05mL oxygen produced per hour which was divided by the mass of the organisms (6g) used in the experimental tube.
rate of oxygen production=0.05ml/hour6 g=0.008
For this tube, the rate of oxygen production was, therefore, 0.008ml of oxygen produced per hour per gram of Ceratophyllum
The rate of photosynthesis for the organisms in tube 2 in, group 2 was calculated as follows. The slope had a gradient of 0.105mL oxygen produced per hour which was divided by the mass of the organisms (6g) used in the experimental tube.
rate of oxygen production=0.105ml/hour6 g0.0175
For this tube, the rate of oxygen production was, therefore, 0.0175ml of oxygen produced per hour per gram of Ceratophyllum.
The rate of photosynthesis for the organisms in control tube, in group 2, was calculated as follows. The slope had a gradient of 0.0225mL of oxygen produced per hour.
The rate of photosynthesis for the organisms in tube 1, in group 3 was calculated as follows. The slope had a gradient of 1mL oxygen produced per hour which was divided by the mass of the organisms (6g) used in the experimental tube.
rate of oxygen production=1ml/hour6 g=0.167
For this tube, the rate of oxygen production was, therefore, 0.167ml of oxygen produced per hour per gram of Ceratophyllum
The rate of photosynthesis for the organisms in tube 2, in group 3 was calculated as follows. The slope had a gradient of 1.9mL oxygen produced per hour which was divided by the mass of the organisms (6g) used in the experimental tube.
rate of oxygen production=1.9ml/hour6 g=0.32
For this tube, the rate of oxygen production was, therefore, 0.32ml of oxygen produced per hour per gram of Ceratophyllum
The rate of photosynthesis for the organisms in control tube, in group 3 was calculated as follows. The slope had a gradient of 0.2mL of oxygen produced per hour.
The rate of photosynthesis for the organisms in tube 1 in group 4 was calculated as follows. The slope had a gradient of 0.45mL oxygen produced per hour which was divided by the mass of the organisms (6g) used in the experimental tube.
rate of oxygen production=0.45ml/hour6 g=0.075
For this tube, the rate of oxygen production was, therefore, 0.075ml of oxygen produced per hour per gram of Ceratophyllum
The rate of photosynthesis for the organisms in tube 2 in group 4 was calculated as follows. The slope had a gradient of 0.9mL oxygen produced per hour which was divided by the mass of the organisms (6.05g) used in the experimental tube.
rate of oxygen production=0.9ml/hour6.05 g=0.149
For this tube, the rate of oxygen production was, therefore, 0.149ml of oxygen produced per hour per gram of Ceratophyllum
The rate of photosynthesis for the organisms in control tube in group 4 was calculated as follows. The slope had a gradient of 0mL of oxygen produced per hour.
The rate of photosynthesis for the organisms in tube 1 in group 5 was calculated as follows. The slope had a gradient of 0.65mL oxygen produced per hour which was divided by the mass of the organisms (6g) used in the experimental tube.
rate of oxygen production=0.65ml/hour6 g=0.108
For this tube, the rate of oxygen production was, therefore, 0.108ml of oxygen produced per hour per gram of Ceratophyllum
The rate of photosynthesis for the organisms in tube 2 in group 5 was calculated as follows. The slope had a gradient of 0.85mL oxygen produced per hour which was divided by the mass of the organisms (6g) used in the experimental tube.
rate of oxygen production=0.85 ml/hour6 g0.142
For this tube, the rate of oxygen production was, therefore, 0.142 ml of oxygen produced per hour per gram of Ceratophyllum
The rate of photosynthesis for the organisms in control tube in group 4 was calculated as follows. The slope had a gradient of 0mL of oxygen produced per hour.
Treatment 2
The pipette readings indicated the cumulative amount of oxygen that was produced during photosynthesis. These measurements were recorded in the Cabomba (Table 2).
Calculations
Photosynthetic Rate
Photosynthetic Rate Calculations
The rate of photosynthesis for each experimental and control tube in treatment 2 was calculated using the gradients of the slopes obtained after plotting a graph of cumulative oxygen produced against time in hours (Figure 2). Drawing a line of best fit for all the graphs gave a line with a gradient that was taken to be the rate of oxygen production per hour. To determine the rate of oxygen production per hour per gram of an organism, the gradient of the slope was divided by the mass of the organism used.
The rate of photosynthesis for the organisms in tube 1 in group 1 was calculated as follows. The slope had a gradient of 1.5mL oxygen produced per hour which was divided by the mass of the organisms (6g) used in the experimental tube.
rate of oxygen production=1.5ml/hour6 g0.25
For this tube, the rate of oxygen production was, therefore, 0.25ml of oxygen produced per hour per gram of Cabomba
The rate of photosynthesis for the organisms in tube 2 in group 1 was calculated as follows. The slope had a gradient of 1.95mL oxygen produced per hour which was divided by the mass of the organisms (6g) used in the experimental tube.
Photosynthetic rate=1.95ml/hour6 g=0.325
For this tube, the rate of oxygen production was, therefore, 0.325ml of oxygen produced per hour per gram of Cabomba
The rate of photosynthesis for the organisms in control tube in group 2 was 0mL of oxygen produced per hour per gram of Cabomba.
The rate of photosynthesis for the organisms in tube 1 in group 2 was calculated as follows. The slope had a gradient of 3.8mL oxygen produced per hour which was divided by the mass of the organisms (5.92g) used in the experimental tube.
rate of oxygen production=3.8ml/hour5.92 g=0.64
For this tube, the rate of oxygen production was, therefore, 0.64ml of oxygen produced per hour per gram of Cabomba
The rate of photosynthesis for the organisms in tube 2 in group 2 was calculated as follows. The slope had a gradient of 1.5mL oxygen produced per hour which was divided by the mass of the organisms (6.02g) used in the experimental tube.
rate of oxygen production=1.5ml/hour6.02 g=0.25
For this tube, the rate of oxygen production was, therefore, 0.25ml of oxygen produced per hour per gram of Cabomba.
The rate of photosynthesis for the organisms in control tube in group 2 was 0mL of oxygen produced per hour per gram of Cabomba.
The rate of photosynthesis for the organisms in tube 1 in group 3 was calculated as follows. The slope had a gradient of 3.75mL oxygen produced per hour which was divided by the mass of the organisms (5.99g) used in the experimental tube.
rate of oxygen production=3.75ml/hour5.99 g0.626
For this tube, the rate of oxygen production was, therefore, 0.626ml of oxygen produced per hr per gram of Cabomba
The rate of photosynthesis for the organisms in tube 2 in group 3 was calculated as follows. The slope had a gradient of 4.15mL oxygen produced per hour which was divided by the mass of the organisms (6.02g) used in the experimental tube.
rate of oxygen production=4.15ml/hour6.02 g=0.69
For this tube, the rate of oxygen production was, therefore, 0.69ml of oxygen produced per hr per gram of Cabomba.
The rate of photosynthesis for the organisms in control tube in group 3 was 0mL of oxygen produced per hour per gram of Cabomba.
The rate of photosynthesis for the organisms in tube 1 in group 4 was calculated as follows. The slope had a gradient of 3.125mL oxygen produced per hour which was divided by the mass of the organisms (5.99g) used in the experimental tube.
rate of oxygen production=3.125ml/hour5.99 g=0.52
For this tube, the rate of oxygen production was, therefore, 0.52ml of oxygen produced per hr per gram of Cabomba
The rate of photosynthesis for the organisms in tube 2 in group 4 was calculated as follows. The slope had a gradient of 2.575mL oxygen produced per hour which was divided by the mass of the organisms (6.02g) used in the experimental tube.
rate of oxygen production=2.575ml/hour6.02 g0.428
For this tube, the rate of oxygen production was, therefore, 0.428ml of oxygen produced per hr per gram of Cabomba
The rate of photosynthesis for the organisms in control tube in group 4 was 0.132mL of oxygen produced per hour.
The rate of photosynthesis for the organisms in tube 1 in group 5 was calculated as follows. The slope had a gradient of 2mL oxygen produced per hour which was divided by the mass of the organisms (5.93g) used in the experimental tube.
rate of oxygen production=2ml/hour5.93 g=0.337
For this tube, the rate of oxygen production was, therefore, 0.337ml of oxygen produced per hour per gram of Cabomba.
The rate of photosynthesis for the organisms in tube 2 in group 5 was calculated as follows. The slope had a gradient of 3.2mL oxygen produced per hour which was divided by the mass of the organisms (5.87g) used in the experimental tube.
rate of oxygen production=3.2 ml/hour5.87 g=0.545
For this tube, the rate of oxygen production was, therefore, 0.545ml of oxygen produced per hour per gram of Cabomba.
The rate of photosynthesis for the organisms in control tube in group 5 was 0mL of oxygen produced per hour per gram of Cabomba.
The graphs of the mean oxygen produced per hour for the different treatments and their associated control was plotted as shown in Figure 3 below.
Tables and Figures
Figure 1: A graph of cumulative oxygen produced in mL against time in hours for the Ceratophyllum organisms
Figure 2: A graph of cumulative oxygen produced in mL against time in hours for the Cabomba organisms
Figure 3: A graph of mean oxygen produced per hour for the different Treatments
Discussion
Photosynthesis, which is a process that takes place in algae, plants, and some types of bacteria, is the process through which these organisms utilize light energy to make food using carbon dioxide. The process gives out oxygen one of the bi-products (Toole & Toole, 2004). The rate at which photosynthesis takes place is usually affected by a number of factors such as light intensity, carbon dioxide and temperature. An increase in the level of these factors increases the rate at which photosynthesis occurs and reduction of the factors reduce rate of photosynthesis (Mishra, 2004).
Both Cabomba and Ceratophyllum are submerged plants and are mainly found in ponds Cabomba belongs to the Cabombaceae family (Bremer, et al., 2009) and are mainly used by aquarists in oxygenating fish tanks. Ceratophyllum are also known as hornworts and are also found in streams and marshes.
This experiment aimed to compare the rate of photosynthesis both in Cabomba and Ceratophyllum organisms by measuring the amount of oxygen produced by a given amount of the organisms. From the results, the difference in rate of oxygen production in Ceratophyllum was less than the rate in Cabomba. This results in rejection of the null hypothesis that said that the rate of photosynthesis in the two organisms were similar. The results also differed from the prediction that was set that Cabomba had the lowest rate of photosynthesis as reported earlier (Van, Haller, & Bowes, 1976). It can thus be concluded that, the two organisms that were examined had different rates of photosynthesis with Cabomba having the highest photosynthetic rate and Ceratophyllum having the lowest.
Reference List
Bremer, B., Bremer, K., Chase, M., Fay, M., Reveal, J., Soltis, D., & Stevens, P. (2009). An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG III. Botanical Journal of the Linnean Society, 161(2), S105-121.
Mishra, S. (2004). Photosynthesis in Plants. Grand Rapids: Discovery Publishing House.
Toole, G., & Toole, S. (2004). Essential A2 Biology for OCR. Cheltenham: Nelson Thornes.
Van, T. K., Haller, W., & Bowes, G. (1976). Comparison of the Photosynthetic Characteristics of Three Submersed Aquatic Plants. Plant Physiology, 58(6), 761-768.
