Investigate_the_Effect_of_Bicarbonate_Concentration_on_the_Rate_of_Photosynthesis_in_Asystasia_Leaves

Investigate The Effect Of Bicarbonate Concentration On The Rate Of Photosynthesis In Asystasia Leaves Lucas T. Background information Photosynthesis is the process by which autotrophic organisms use light energy to convert carbon dioxide into sugars as their form of nutrition. Plants, algae and many species of bacteria carry out photosynthesis. Photosynthesis uses carbon dioxide and water, releasing oxygen as a waste product: light energy captured by chlorophyll 6 CO2 + 6 H2O C6H12O6 + 6 O2 This is a simplified equation of the two types of chemical reactions that occur in chloroplasts. They are the light dependent and light independent reactions. During the day, the limiting factor for photosynthesis is usually the amount of carbon dioxide and this is what will be investigated in this experiment. The rate of photosynthesis can be measured by measuring the rate of oxygen produced. The leaf discs are extracted from the same area as much as possible to minimise inaccuracies caused by differences in chlorophyll density in different areas of the leaf. They are prepared for the experiment by subjecting them to a low-pressure environment so that air will come out of the leaf discs, causing them to sink. In this way, the time taken for them to float back up is measured, because a faster time means that the rate of photosynthesis is faster, so oxygen is produced faster in the leaf and this lowers the density of the leaf disc, causing it to float. The time taken for the first three leaf discs to float up is measured so that if one leaf disc is a special case and a result significantly different from the others, it will not affect the results so much. In other words, an anomaly will not have that great an impact on the results. Aim To investigate the effect of carbon dioxide concentration on the rate of photosynthesis in leaves Hypothesis The greater the concentration of carbon dioxide, the faster the rate of photosynthesis Variables Independent Concentration of sodium hydrogen carbonate solution Dependent Rate of photosynthesis Controlled Temperature Light intensity Light wavelength Materials Freshly plucked Asystasia leaves 0.5M solution of sodium hydrogen carbonate Hole puncher 50 ml measuring cylinder 10ml syringe 50ml beakers Stopwatch Procedure 1. Prepare five 50 ml beakers with “0.500M”, “0.250M”, “0.125M” and “0.100M” concentrations of sodium hydrogen carbonate. 2. Prepare leaf discs a) b) c) Punch out 20 leaf discs from the same leaf with the whole puncher Place 5 leaf discs in the syringe and put the plunger in place Aspirate 10 ml of 0.500M sodium hydrogen carbonate solution into the syringe, letting out as much air as possible d) e) Invert the syringe and place your finger over the nozzle Pull the plunger down repeatedly. The leaf discs should sink after a few repetitions f) Place the contents of the syringe back into the beaker with the corresponding solution concentration g) Repeat steps b-f with the other 3 concentrations 3. Quantifying the rate of photosynthesis a) Place the prepared beaker with leaf discs directly under lamp and start the stopwatch b) Record the time it takes for each of the first three leafs to float to the surface of the solution c) Repeat steps a and b with the other concentrations Raw data Table 1 Time / min Concentration/M 1 0.500 0.250 0.125 0.100 5.23 6.57 7.67 15.8 2 5.40 6.72 7.72 16.9 3 5.83 6.87 8.22 18.8 Processed Data Table 2 Concentration/M 0.500 =5.49 0.250 0.125 0.100 Graph 1 6.72 7.87 17.2 0.122 0.248 1.24 Average time /min (5.23+5.40+5.83)/3 0.252 =0.182 0.149 0.127 0.0581 S.D. Rate /min-1 1 / 5.49 Rate of photosynthesis against concentration of sodium hydrogen carbonate solution 0.2 0.15 0.1 0.05 0 0 0.1 0.2 0.3 0.4 0.5 0.6 Concentration /M Discussion Results and conclusion The results confirm the hypothesis that the greater the concentration of sodium bicarbonate solution, the faster the rate of photosynthesis. From Graph 1, it can also be seen that the concentration affects the rate of photosynthesis greatly at around 0.1M to 0.125M, but after that the rate of photosynthesis is only increased slightly. Standard deviation is used in Table 2 to confirm that the values for each concentration do not vary too much; they are close enough to confirm that the rate of photosynthesis is indeed affected by the concentration of sodium hydrogen carbonate solution. Rate / min^(-1) Evaluation and Limitations When pulling the plunger several times in the syringe, a longer exposure to a low pressure would cause the leaf disc to become denser and thus require more time to float up. In this way, the leaf discs in each concentration could have different densities at the start of the experiment, which could have affected the results. Secondly, even though we tried to keep the light intensity for the experiment the same for all concentrations, there will be slight errors due to small changes in the position of the beaker, light, leaf discs, level of solution and many other factors. However, the effect of such should be negligible and should not affect the results much because the setup is generally identical. During the experiment, temperature change is inevitable due to heat released from the lamp, and temperature is one of the factors of photosynthesis. However, the effect of such should be negligible because, firstly, the temperature change is small, and secondly, every solution is subject to the same light intensity, so they would be heated evenly until the first three leaf discs float up in the solutions. Bibliography 1. D. Y. Ryu, K. Shin, E. Drockenmuller, C. Hawker and T. P. Russell. Science. 2005, 308, 236-239. 2. http://plantphys.info/seedg/seed3.html 3. www.kabt.org/wp-content/uploads/2008/08/floating-leaf-assay.doc All pages last accessed on 17th April 2009.