1. Honori Yamada Biology SL 2 Mar/12/11 The Effect of the Rate of Photosynthesis on Different LeavesIntroduction: Oppositely from cellular respiration, photosynthesis is a chemical reaction inwhich autotrophs or green plants produce their own food and as a byproduct, theysynthesize glucose and oxygen. In order for photosynthesis to process, threefundamental inorganic compounds are needed along with the plant: carbon dioxide(CO2), water (H2O), and light intensity. This overall reaction of the photosynthesisprocess can be written as a equation:6H2O + 6CO2  C6H12O6+ 6O2(1)where6H2O indicates six water molecules, 6CO2are six carbon dioxides, C6H12O6 isglucose, and 6O2 refers to six oxygen molecules. The process of photosynthesis showshow photosynthetic organisms store light energy, water, and carbon dioxide to createglucose and oxygen. Oxygen is released in the atmosphere whereas glucose is used at alater time to supply the energy needs of the cell. Combining of these elements to produce sugar and oxygen takes place in thechloroplast which includes chlorophylls that associate with the action of the greenpigment. A pigment is any substance that absorbs light. The wavelength of the lightreflected or absorbed determines each color of the pigment. Chlorophyll, which is agreen color pigment, tends to absorb all wavelengths of visible light except green. Sincechlorophylls do not absorb the light with the specific wavelength of color green, itreflects back to be detected by our eyes. This is the reason why leaves are green; thecolor green could not be absorbed by the chlorophylls in the cells that the light reflectsback to our eyes making it visible for humans to see. In this research, the experiment will be investigated on whether the color of theleaves will affect the rate of photosynthesis. Throughout this experiment, 15 holepunched disks of leaves will be placed in a water filled syringe to such out the oxygen inthe leaf disks by drawing back the plunger to create vacuum. Then, the leaf disks will beinserted into a 2% sodium bicarbonate (NaHCO3) solution. Photosynthesis will furtheroccur when the leaf disk inserted solution is placed where the light from the lamp isdirectly shined through, making it a light-dependent reaction. The leaf disks aregradually going to create oxygen that will change the buoyancy – causing the disks tofloat. At first, the leaf disks in the water filled syringe all float because the disks insistsmall oxygen particles. However, since this experiment tests the rate of photosynthesisin the leaves, the leaf disks are drawn back with a plunger in order to suck out the
2. Honori Yamada Biology SL 2 Mar/12/11oxygen until each pieces sink. During this experiment, sodium bicarbonate, that hascarbonate ions will be used as it serves as the carbon source for photosynthesis. Assodium bicarbonate dissolves in water, carbonate ions appear as it absorbs into the leafdisks – making it a carbon dioxide gas. Therefore, sodium bicarbonate will be usedthroughout this lab in order to quicken the rate of photosynthesis.Design:Research Question:How will the difference in the color of the leaves affect the rate of photosynthesis?Table 1: Important VariablesVariable Type HowTypes of Leaves Independent Variable Picked up 2 different leaves with different colors (light, dark)Length of time (rate of Dependent Variable Stopwatchphotosynthesis)Circumference of leaf disks Controlled Variable Hole puncherConcentration of solution Controlled Variable Electronic Balance, beaker, - Amount of sodium water, stirrer, sodium bicarbonate bicarbonate - Amount of waterTemperature Controlled Variable Water tank, thermometerSize of Beaker Controlled Variable -------------Light intensity Controlled Variable Ruler, pencil, beaker, lampTable 1▲: These are the important independent, dependent, and controlled variablesthat are shown as well as the process of how it was done.Materials: - Leaves (2 types) - Hole puncher - Syringe - Beaker - Water - Sodium bicarbonate - Thermometer Figure 1: Sodium Bicarbonate, - Electronic Balance syringe, beaker, stopwatch, - Stopwatch leaf A and B are shown. Figure 2:The water tank and - Water Tank - Lamp the lamp are shown which controlled the temperature
3. Honori Yamada Biology SL 2 Mar/12/11Procedure: 1. Prepare a beaker and add 1g of sodium bicarbonate on an electronic balance 2. Get a water tank and fill the water about half way through 3. Prepare the experiment by placing the water filled tank in front of the lamp then the beaker in front of the tank so that the light shines through the water tank, then to the beaker in order to keep the temperature controlled(Figure 3) 4. Trace a mark of the beaker onto the table so that the light intensity would also be controlled 5. Go outside and find two different types of leaves with a different color (one light green, one dark green) 6. Hole punch 15 pieces of disks from one type of leaf 7. Place the 15 disks into the syringe 8. Prepare 50ml of water and draw in the water with the syringe (the disks should all float) 9. Hold a finger over the syringe opening and draw back on the plunger to create vacuum for 30 seconds 10. Repeat the vacuum until all the leaf disks sink to the bottom 11. Hold a finger over the syringe opening and remove the plunger 12. Pour in most of the water in the syringe into the beaker with the sodium bicarbonate and stir it will 13. After the solution is mixed, pour in the rest of the water with the disks 14. Insert a thermometer to keep the temperature controlled and consistent 15. Once the lamp is switched on, start the stopwatch and record the dataFigure 3▲: The figure above shows the setting of the experiment so that the light doesnot affect the rate of photosynthesis by using a water tank.
4. Honori Yamada Biology SL 2 Mar/12/11Data Collection and Processing:Table 2:Time Length for Leaf A Disks to Float# of floated Trial 1 (sec) Trial 2 (sec) Trial 3 (sec) Trial 4 (sec)disks1 34 107 73 62 55 187 92 253 62 226 116 634 216 246 147 1075 235 266 168 1236 254 267 218 1367 277 276 229 1478 289 284 242 1629 323 298 252 17310 345 322 260 216Table 2▲: The table above shows four trials of the time it took for all ten disks for Leaf Ato float.Table 3:The Rate of Photosynthesis for each Trials and its Average Average Rate ofGroups: Trial 1 Trial 2 Trial 3 Trial 4 Photosynthesis (sec) (sec) (sec) (sec)10th Disk time 345 322 260 216 0.0036 ± 0.0009Rate of 0.0029 0.0031 0.0038 0.0046PhotosynthesisTable 3▲:The table above shows the calculated rate of photosynthesis of the four trialsand the average rate of photosynthesis for Leaf type A.Table 4: Time Length for Leaf B Disks to Float# of floated Trial 1 (sec) Trial 2 (sec) Trial 3 (sec) Trial 4 (sec)disks1 756 536 785 6322 787 569 970 6513 874 605 1105 7894 1142 622 1138 9975 1285 992 1162 11636 1349 1032 1202 11827 1369 1041 1246 11968 1396 1052 1337 12139 1405 1206 1415 123510 1453 1238 1457 1386Table 4▲: The table shows four trials of the time it took for all ten disks for Leaf B tofloat.
5. Honori Yamada Biology SL 2 Mar/12/11Table 5: The Rate of Photosynthesis for each Trial and its Average Average Rate ofGroups: Trial 1 Trial 2 Trial 3 Trial 4 Photosynthesis (sec) (sec) (sec) (sec)10th Disk time 1453 1238 1457 1386 0.00073 ± 0.00012Rate of 0.00069 0.00081 0.00069 0.00072PhotosynthesisTable 5▲:The table above shows the calculated rate of photosynthesis of the four trialsand the average rate of photosynthesis for Leaf type B.Sample Calculations: i. Changing the Time from Minutes to Seconds (Leaf B Trial 1 Disk 10) = minutes × 60 + seconds = 24 × 60 + 13 1453 seconds ii. Calculating the Rate of Photosynthesis (Leaf A Trial 1) = 1/time length it took for the 10th disk to float = 1/345 0.0029 (s-1) iii. Calculating the Average Rate of Photosynthesis (Leaf A) = (Add the rate of photosynthesis for all four trials)/4 = (0.0029 + 0.0031 + 0.0038 + 0.0046) / 4 0.0036 (sec) iv. Calculating the Uncertainties (Leaf A) = range of the rate photosynthesis /2 = (0.0046 – 0.0029) / 2 = 0.0017 / 2 ±0.0009
6. Honori Yamada Biology SL 2 Mar/12/11Figure 4▲:The graph above shows the difference of the average rate of photosynthesiswith leaf type A and B.T-Test Results:Using the statistical program from the site of http://graphpad.com/quickcalcs, theunpaired T-test was performed for all the 80 raw data of Leaf A and B.P value and statistical significance: The two-tailed P value is less than 0.0001 By conventional criteria, this difference is considered to be extremely statisticallysignificant.Confidence interval: The mean of Leaf A minus Leaf B equals -886.15 95% confidence interval of this difference: From -977.33 to -794.97Intermediate values used in calculations: t = 19.3491 df = 78 standard error of difference = 45.798
7. Honori Yamada Biology SL 2 Mar/12/11Review your data: Table 6: The Statistical Difference of Leaf A and B Group Leaf A Leaf B Mean 188.10 1074.25 SD 92.40 274.52 SEM 14.61 43.41 N 40 40Table 6▲: The table above shows the results of the differences in the two types of leavesby the T-test.Conclusion & Evaluation:Conclusion: According to graph in figure 4, there is a great different in the average rate ofphotosynthesis for leaf A and B. With leaf A, the rate of photosynthesis was 0.0036s-1whereas with leaf B, the rate was 0.00073 s-1having the difference of around 0.00029s-1.This relatively huge difference in the average rate between the two types of leaves signifythat the rate of photosynthesis can be effected by the type of leaves. As leaf B has asmaller rate than leaf A, this shows how leaf B took a longer time for the process ofphotosynthesis than leaf A. Although this experiment showed a relative difference in thetwo types of leaves, the reason to the result cannot be proven. However, it can bepredicted that either leaf A had more chlorophyll than leaf B, or that leaf B was thickerin size than leaf A. Again, for either reason, it can be concluded that the different type ofleaves do make a difference in the rate of photosynthesis. Not only was the data compared by graphing the rate of photosynthesis, but alsothe unpaired data T-testing was programmed in order to further verify that there is asignificant statistical difference in the two rates of photosynthesis. By adding all fortyraw data for each leaf, the calculation which compared the differences in the two rates ofphotosynthesis showed a statistically significant difference. Below the “ConfidenceInterval”, the mean difference of leaf A and B was886.15. This clearly shows anextremely large difference in rate of photosynthesis. Not only, but even by takingaccount into the statistical error of 5%, the result shows that there will still be asignificant mean difference of 977.33 - 794.97. Therefore, it could be stated bothstatistically and mathematically that the type of leaves do affect the rate ofphotosynthesis. The uncertainties for type A and B were both relatively small. For leaf A, theuncertainty was ± 0.0009whereas for leaf B, the uncertainty was ± 0.00012. This showshow with leaf B, the results were not as consistent as with leaf A. One reason could bebecause of the difference in the amount of chlorophyll in each leaf disks. As leaf A does
8. Honori Yamada Biology SL 2 Mar/12/11not have a big uncertainty amount as leaf B, it could be stated that the results of leaf A ismore reliable than leaf B. Although the raw data consists the time lengths of up to fifteen leaf disks, thisexperiment only measured the first ten leaf disks for a reason. The experiment testedwith fifteen disks in order to lessen the chance of errors. There is a probability that someleaf disks were statistically an outlier. Shown in the raw data, some of disks did not floatup due to some errors that were caused during the process. If the calculations for therate of photosynthesis consisted up to fifteen disks for each trial, errors could haveresulted such as some outliers. Oppositely, using too little data could have resulted withan inaccurate calculation of the rate of photosynthesis as some disks could have floatedtoo fast (oxygen was not completely expunged out of the disks or too many possiblechlorophylls in an area of the leaf disk). To compensate the effect of the outliers, theconcept of Exposure Time or ET50, created by Steucek, is a reliable index to thisresearch. The Exposure Time is the time it takes for half of the process (or 50%) tochange. By using the time it took for the tenth disk to float, it shows a relatively reliableresult of the rates of photosynthesis.Evaluation: Throughout this experiment, there was one big error which was choosing theright type of leaves. On the first day, two different colored leaves were chosen withoutbeing aware of the other differences such as the thickness and the size. This furtheraffected the results since the difference in the rates could have been due to the thicknessof the leaves or the different amount of the chlorophylls in a leaf. Therefore, since thereis more than one solution to why the rates differed with the different types of leaves,nothing could be completely stated. This can be improved by choosing the same type ofleaf which consists of different colors (some parts light green, some parts dark green).This can further make the experiment itself more precise and controlled as it only wouldfocus on whether the “color” of the leaf can affect the rate of photosynthesis. Along with the type of the leaves, the accuracy in expunging all the oxygen out ofthe disks by a syringe could have been an issue. Although the syringe was vacuumeduntil all fifteen disks sunk to the bottom, it was not completely sure that all the oxygenwas out for all the disks, equally. As some of the data for the time length of disks 1-2showed as relatively fast buoyancy change than the others, it could possibly be said thatthe oxygen was not fully expunged for those. This can further be improved by drawingback the plunger for as longer period of time, for example 30 seconds. Although this stillwould not measure that all the oxygen would be out of the disks, there were still be ahigher chance of reliability. To make a 2% solution with 50ml of water, 1g of sodium bicarbonate measuredand used. However, there was difficulty in measuring the exact amount of 1g sodiumbicarbonate. This could have affected the rate of photosynthesis since in some trials,there could have been more carbon ions that would have fasten the rate than the othertrials. This could be improved for next time by doubling the amount of water so that the
9. Honori Yamada Biology SL 2 Mar/12/11amount of sodium bicarbonate would be doubled as well. By doubling the amount ofsodium bicarbonate, it would be easier to measure the exact amount that could becontrolled.Weakness How/what SolveType of Leaves The thickness, size, and the Compare with the same leaf color could have all affected that consist of different the rate of photosynthesis colors (spotted leaves)Expunging oxygen out In data, some disks showed Draw back the plunger for aof Disks Completely a relatively fast buoyancy longer period of time time than the othersConcentration of the Difficulty in measuring Double the amount of waterSolution exactly 1g of sodium so that the amount of Bicarbonate sodium bicarbonate would double as well, making it easier to measure.Amount of Chlorophylls Although used the same Make one or two morein each Disks leaf, each disk could have trials so that the results consisted a different could be more reliable. amount of chlorophyll which could have affected the rate of photosynthesisTable 7▲: The different weaknesses that appeared during the experiment and how itshould be solved is shown