Design Experiment to investigate the effect of the concentration of Sodium Hydrogen Carbonate on the rate of photosynthesis using Cobomba plant. Aim: The aim of the experiment is to investigate the effect of the concentration of Sodium Hydrogen Carbonate (NaHC03) on the rate of photosynthesis using a Cobomba plant. Hypothesis: As the concentration of NaHC03 increases the rate of photosynthesis of the Cobomba plant should increase, as there is a greater presence of a carbon dioxide, obtained from the carbonate, which is a key reactant in photosynthesis.
However it is also expected that the rate of photosynthesis should plateau with reater amounts of NaHC03, because the Cobomba plant will not be able to use all the extra, available C02 as it’s enzymes physically do not have the ability to do so. Background Information: When dissolved in water, NaHC03 produces carbon dioxide gas: . As can be seen in the equation for photosynthesis, carbon dioxide is a reactant in photosynthesis: 6 C02 + 12 H20 + photons -+ C6H1206 + 6 02 + 6 H20. The presence of NaHC03 means that C02 is more readily available in larger quantities, to speed up the process of respiration.
However if a large amount of C02 is present in the water the Cobomba plant will not be able to use it all, as the nzymes cannot function quick enough. Other limiting factors may also cause the rate to slow, such as light intensity. As can be seen in the equation for photosynthesis, 02 is a product of photosynthesis and thus the rate of photosynthesis can be calculated by the amount of 02 released when photosynthesis occurs. Variables: Independent Dependent Controlled How to measure/control Amount of NaHC03 added to water Using the same weighing scale and weighing boat each time to measure the amount of NaHC03.
Also using fresh tap water each time, so that the concentration of NaHC03 would be exact Amount of oxygen released Measured using the water bath and 100cm3 measuring cylinder Temperature of water Stayed in the same room, and used a heat barrier to prevent any heat from the lamp from affecting the rate of photosynthesis. Light intensity Used a lamp, kept in the same position each time to keep the light intensity equal for each repeat. pH of water Used tap water each time, and used fresh tap water for every measurement to ensure no NaHC03 was left in the water.
Apparatus Application/Justification 1 x 500cm3 beaker To contain water to allow the NaHC03 to dissolve in 1 x glass funnel To put Cobomba plant under so that oxygen released goes into the easuring cylinder 1 x 10cm3 measuring cylinder To collect oxygen that is released Cobomba plant The plant which will respire and provide the results 5gof NaHC03 It will dissolve in water to release C02 which will affect the rate of respiration 100cm3 measuring cylinder To act as a heat shield from the light Lamp To ensure that the Cobomba plant has a constant light source to enable photosynthesis.
Weighing scale and boat To measure the amount of NaHC03 Glass stirring rod To stir the NaHC03 when it is put in water to evenly distribute the concentration Stopwatch To ensure that time lengths are accurate for each time the xperiment is carried out Scissors To cut the Cobomba stem Ruler To measure length of Cobomba plant Method: 1. Measure a length of IOcm of Cobomba plant using the ruler 2. Fill the 500cm3 beaker, up to 500cm3, with tap water and place the Cobomba in the water underneath the glass funnel 3.
Place the 10cm3 measuring cylinder upside down on top of the funnel, and ensure that it fills up with water 4. Set up a heat barrier using the 100cm3 measuring cylinder and fill it with water. Place it in between a lamp and the 500cm3 beaker 5. Switch on the lamp and start the timer 6. Once four minutes has passed stop the timer, and note down what the volume of 02 is in the measuring cylinder 7. Start the timer again, and after six minutes stop it. Note down the volume of 02 in the measuring cylinder 8. From this it can be deduced how much 02 has been collected 9. Repeat steps 1-4, but next measure 0. g of NaHC03 using the weighing boat and the weighing scales 10. Add the NaHC03 to the beaker and stir it with the glass rod 11. Start the timer and stop it after four minutes to allow the Cobomba to adjust to the water with added NaHC03, and make sure to note down the volume of 02 after four minutes 12. Then start the timer again for a further so minutes. When this time is up write down the volume, and from that it can be deduced how much 02 has been released 13. Repeat steps 10-12, making sure to replace the water in the beaker each time with new water, but adding another 0. gof NaHC03 each time 14. Repeat steps 1-13 a minimum of four more times to allow an average to be obtained Risk Assessment: Risk Precaution Being burnt by the lamp Take care and move slowly Swallowing a large quantity of NaHC03 or getting it in your eyes Do not put NaHC03 near to face 02 Amount of NaHC03 (g) +1- 0. 001 g Volume of 02 collected (cm3) +1- 0. 1 cm3 2 3 4 5 Average (2 s. f) Standard Deviation (2 s. f) 0 0. 2 0. 1 0. 2 0. 1 0. 2 0. 16 0. 05 0. 5 1. 0 1. 5 2. 0 2. 5 0. 2 0. 3 0. 4 0. 6 0. 7 0. 1 0. 8 0. 28 0. 44 0. 72 0. 06 0. 07 0. 05 0. 4 Graph to show the amount of 02 released with different amounts of NaHC03 from photosynthesis attached Discussion: The results show a positive correlation that evidences that as the amount of NaHC03 increases, so does the volume of 02 collected. This shows that NaHC03 speeds up the rate of photosynthesis, as all each amount time the experiment was done the time limits were kept the same but with more NaHC03 the olume of 02 increased. Therefore this partly proves the hypothesis, because it is shown that the addition of more C02, provided by the NaHC03, increases the rate of photosynthesis.
However the rate of photosynthesis did not begin to plateau, as the hypothesis had stated. This may have been because there was not a great enough range of measurements of NaHC03 used to allow this pattern to be shown. Evaluation: The time restraints were quite limiting, and had there been more time a greater amount of repeats could have been done which would have allowed a more accurate average to be calculated. ?? A systematic human error was not being able to add the NaHC03 to the water at the same time as starting the stop clock, which means there may have been a difference of a few seconds between each time the experiment was done. ?? The act of measuring was not as precise as it could have been, and to resolve this equipment with a greater degree of accuracy could have been used. ??? Another error was the decision to use small amounts of NaHC03. The consequence of this was that the digits of the results obtained were very small. Not only did this make them hard to measure, but also it meant that there was not a hugely significant ifference with the amounts of NaHC03 added to the water. Furthermore the ratio of for a comparatively large volume of water. Therefore a greater amount of NaHC03 should be used if this experiment were to be repeated again. ?? Another human error was the repeated use of the same Cobomba plant. This may have affected the results, because the plant will have been respiring for a long time and also may still have remains of NaHC03 on it that would not make the next measurement of NaHC03 precise. To solve this the same mass of Cobomba plant, but from a different stem, could have been used each time. However this also poses problems as different stems may respire at different rates in the first place. ??? If time had allowed then the time that the plant was given to respire could have been extended.
This would have given a greater volume of 02, and the results may be clearer. ??? An increased range of NaHC03 masses could be used, and this would hopefully show the results as expected in the hypothesis. ???The light intensity in the room may have changed during the time the experiment was done in, as it was turning into evening, and this may have had an affect on the results. To improve this, the experiment ould have been carried out in a dark room, but with several lamps shining on the beaker with heat barriers in front of them.
This would have allowed the light intensity to remain constant. Conclusion: To conclude, it can be seen from the results obtained in the experiment that the rate of photosynthesis of the Cobomba plant increases with an increased amount of NaHC03 in its surrounding water. Therefore this suggests that C02 has an affect on photosynthesis, and that with greater amounts of it available there is a greater rate of photosynthesis. Bibliography: 1B Study Guides, Biology, Oxford, Andrew Allott Appendix: Attached