The Effects of Different Carbon Dioxide Concentrations on Photosynthetic RateQuestionHow does carbon dioxide affect the rate of photosynthesis?Background-The equation for photosynthesis is:6CO2 + 6H2O = C6H12O6 + 6O2 + H2O-When photosynthesis occurs in leaf discs in a solution, small oxygen bubbles form on the discs that will eventually cause them to float to the top of the solution-Leaf discs float in a solution until oxygen is drawn out of the space by creating a vacuum-Leaf discs placed in a bicarbonate solution, created by mixing baking soda and water, are able to photosynthesizeHypothesisIf leaf discs taken from English ivy are exposed to varying concentrations of bicarbonate solutions, then photosynthesis will occur at the fastest rate in the bicarbonate solution that is most highly concentrated because carbon dioxide and water are the reactants of photosynthesis.Materials-goggles-gloves-baking soda-distilled water-liquid soap-10ml plastic syringes-English ivy leaves-single hole punch-4 200ml cups-graduated cylinder-plastic tray-scale-lamp-timer-plastic spoon-beakerVariables and Controls-Independent Variable: concentration of the bicarbonate solutions-Dependent Variable: floating leaf discs-Controlled Variables: light source, plastic cup, temperature; one cup held a bicarbonate solution without added soap to act as a control groupProcedurePunch 40 leaf discs from the English ivy leaves.Make 4 sodium bicarbonate solutions (1g/350ml with 1-2 drops of diluted soap solution, 5g/350ml with 1-2 drops of diluted soap solution, 10g/350ml with 1-2 drops of diluted soap solution, and 1g/350ml with no soap).Fill 4 cups with 200ml of each of the four solutions.
Place 10 leaf discs in a syringe. Push the plunger of the syringe down all the way, so that there is no oxygen left in the syringe, but do not crush the discs.Draw 5ml of the first solution from the cup (1g/350ml with diluted soap solution) into the syringe.Turn the syringe upside down and place a finger over the end. Pull up on the plunger to create a vacuum.Release the vacuum; the leaf discs should sink.
Put the discs and liquid back into the cup containing the solution from which they came.Repeat steps 4-8 with the other three solutions.Expose the cup to light and record how many discs are floating at the end of each minute. Record in table.
Continue observing until all discs are floating.When all of the discs are floating, cover the cup with aluminum foil and put it somewhere dark. At the end of each minute, observe how many discs are still floating.Repeat steps 10-12 with the other three solutions.Data and ObservationsNumber of Leaf Discs Floating at the End of Each Minute While in LightTime (Min)1g/350ml with soap5g/350ml with soap10g/350ml with soap1g/350ml without soap100002000033000480005100006100007100008100009100001010000111020012103001310530141056015106100161071021710810418109107191010109Number of Leaf Discs Floating at the End of Each Minute While in DarkTime (Min)1g/350ml with soap5g/350ml with soap10g/350ml with soap1g/350ml without soap199101029781035810104551010AnalysisET50:Solution 1: 3.4Solution 2: 13Solution 3: 12.
3Solution 4: 16.31/ET50, the inverse of ET50, shows the photosynthetic rate at differing bicarbonate concentrations.Total Respiration Rate Calculations:Solution 1 (1g/350ml with soap): 0.6275Solution 2 (5g/350ml with soap): 0.3269Solutions 3 and 4 could not be obtained.Standard DeviationMean: 45 (sum of ET50 values) divided by 4 (number of values) = 11.25(3.
4-11.25)2 + (13-11.25)2 + (12.3-11.25)2 + (16.3-11.25) = 91.2991.
29 divided by 4 = 22.823Square root of 22.823 = 4.777Standard Error4.777 divided by (sqrt4) = 1.194ConclusionThe function of the sodium bicarbonate in this experiment is to provide carbon dioxide, allowing photosynthesis to occur. The leaf discs rise due to photosynthesis converting the carbon dioxide to oxygen, which occupies the gas spaces in the leaf discs. The leaf discs sink due to the bicarbonate solution filling the gas spaces in the discs.
Increasing the concentration of bicarbonate solution resulted in an increase in the time it took for the leaf discs to photosynthesize; the photosynthetic rate was slower. Increased concentrations of the bicarbonate solution also caused respiration to occur more slowly. The rate of photosynthesis for the experiment, based on an average of the two photosynthetic rates able to be calculated, was 0.4772. The hypothesis that leaf disc photosynthesis will occur at the fastest rate in the most highly concentrated bicarbonate solution is refuted by the data because photosynthesis rates slowed as bicarbonate concentration increased. Photosynthesis limiting factors include temperature, light intensity, and carbon dioxide concentration.
Possible errors include damaged leaf discs when attempting to sink them in preparing the solutions, temperature variations throughout the experiment, varying light intensities between experimental groups, and/or inability to provide complete darkness at the end of the experiment to measure respiration. All plants do not have the same respiration rates due to environmental factors and plant type, as well as differences in leaf and roof nutrients. In the future, the experiment could be improved by ensuring the same temperature, light intensity, and darkness for all experimental groups. Future experiments could be conducted measuring the lowest amount of bicarbonate solution at which plants will continue to photosynthesize.