Biology Yeast Experiment

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 (NaHCO3) on the rate of photosynthesis using a Cobomba plant.

Hypothesis: As the concentration of NaHCO3 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 greater amounts of NaHCO3, because the Cobomba plant will not be able to use all the extra, available CO2 as it’s enzymes physically do not have the ability to do so.

Background Information: When dissolved in water, NaHCO3 produces carbon dioxide gas: . As can be seen in the equation for photosynthesis, carbon dioxide is a reactant in photosynthesis: 6 CO2 + 12 H2O + photons → C6H12O6 + 6 O2 + 6 H2O. The presence of NaHCO3 means that CO2 is more readily available in larger quantities, to speed up the process of respiration. However if a large amount of CO2 is present in the water the Cobomba plant will not be able to use it all, as the enzymes 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, O2 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 NaHCO3 added to water Using the same weighing scale and weighing boat each time to measure the amount of NaHCO3. Also using fresh tap water each time, so that the concentration of NaHCO3 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 NaHCO3 was left in the water.

Apparatus:
Apparatus Application/Justification
1 x 500cm3 beaker To contain water to allow the NaHCO3 to dissolve in
1 x glass funnel To put Cobomba plant under so that oxygen released goes into the measuring cylinder
1 x 10cm3 measuring cylinder To collect oxygen that is released
Cobomba plant The plant which will respire and provide the results
5g of NaHCO3 It will dissolve in water to release CO2 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 NaHCO3
Glass stirring rod To stir the NaHCO3 when it is put in water to evenly distribute the concentration
Stopwatch To ensure that time lengths are accurate for each time the experiment is carried out
Scissors To cut the Cobomba stem
Ruler To measure length of Cobomba plant

Method:
1. Measure a length of 10cm 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 O2 is in the measuring cylinder
7. Start the timer again, and after six minutes stop it. Note down the volume of O2 in the measuring cylinder
8. From this it can be deduced how much O2 has been collected
9. Repeat steps 1-4, but next measure 0.5g of NaHCO3 using the weighing boat and the weighing scales
10. Add the NaHCO3 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 NaHCO3, and make sure to note down the volume of O2 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 O2 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 0.5g of NaHCO3 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 NaHCO3 or getting it in your eyes Do not put NaHCO3 near to face

Results: Table showing the mean value of oxygen collected with different amounts of O2
Amount of NaHCO3 (g) +/- 0.001 g Volume of O2 collected (cm3) +/- 0.01 cm3 1
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 0.2 0.2 0.3 0.1 0.2 0.2 0.06
1.0 0.3 0.2 0.3 0.2 0.4 0.28 0.07
1.5 0.4 0.4 0.5 0.4 0.5 0.44 0.05
2.0 0.6 0.7 0.6 0.6 0.5 0.6 0.06
2.5 0.7 0.7 0.7 0.8 0.7 0.72 0.04

Graph to show the amount of O2 released with different amounts of NaHCO3 from photosynthesis attached

Discussion: The results show a positive correlation that evidences that as the amount of NaHCO3 increases, so does the volume of O2 collected. This shows that NaHCO3 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 NaHCO3 the volume of O2 increased. Therefore this partly proves the hypothesis, because it is shown that the addition of more CO2, provided by the NaHCO3, 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 NaHCO3 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 NaHCO3 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 NaHCO3. 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 difference with the amounts of NaHCO3 added to the water. Furthermore the ratio of water and NaHCO3 was not sufficient; as such a small amount of NaHCO3 was used for a comparatively large volume of water. Therefore a greater amount of NaHCO3 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 NaHCO3 on it that would not make the next measurement of NaHCO3 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 O2, and the results may be clearer.
• An increased range of NaHCO3 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 could 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 NaHCO3 in its surrounding water. Therefore this suggests that CO2 has an affect on photosynthesis, and that with greater amounts of it available there is a greater rate of photosynthesis.

Bibliography: IB Study Guides, Biology, Oxford, Andrew Allott

Appendix: Attached

Bibliography: IB Study Guides, Biology, Oxford, Andrew Allott Appendix: Attached