Enzymes are essential to photosynthesis if the enzymes and chlorophyll cannot work very well then my results will be poor, therefore I cannot heat the
As the plant we are testing comes from canada it will probably have a very large temperature range, possibley from around 5C - 30C
The graph's results were taken from my Pilot experiment, which i used to get a rough idea of temperature ranges, and that temperature does dramatically effect the rate of photosynthesis. Other factors that effect photosynthesis are; light intensity and carbon dioxide content. There are also smaller, insignificant factors such as the type of water which could have effected my results.
"Pilot" Diagram
To test my apparatus and theory I did a "Pilot" experiment
Method
For our experiment we chose as accurate equipment as possible to give us the most accurate results. The equipment is as follows:
A Lamp
A boiling tube
A small piece of Elodea
A beaker
The boiling tube was filled with water and the Elodea placed in. The boiling tube was placed in the beaker and the lamp placed at a set length away. He plastic sheets were individually wrapped around the beaker with an elastic band. For every new plastic sheet we counted the number of bubbles each time for a minute. It was important to keep the experiment the same each time to ensure it was fair test for example: The lamp stayed the same distance from the beaker, we used the same plant each time and the plastic sheets were all the same size. The experiment was repeated three times and the results were averaged to ensure they were regular and as expected. Results were recorded each time and patterns observed. Previous results for an experiment of this kind have been recognized and compared. Throughout the experiment we made observations for a number of distinctive things:
· Increase/Decrease in bubbles
· Temperature Increase/Decrease
· Change in Elodea
· Size of bubbles
Variables include:
· Length of Elodea
· Amount of water
· Distance of lamp
· Size of boiling tube
· Transparency of sheets
· Time spent counting
Changing either of the variables would have had effects on the end results; we kept ours all the same each time to ensure a fair test.
Results
As predicted, the results conclude that using sheets with colours near the red and blue end of the spectrum produce a higher amount of bubbles than those near green. Thereby proving that photosynthesis is increased with certain colours of light.
Conclusion
In observation of the results, I have seen how the rate of photosynthesis in the Elodea has been affected by the various factors. In reference to the prediction, I was correct in that the red and blue coloured sheets produced the highest rate of photosynthesis, whereas the sheets, which were green and yellow, resulted in the least bubbles. I feel that we had taken enough measurements to be sure of a fair test as the experiment was repeated several times so. Each plastic coloured sheet we used had the same time, and variables as the others so we obtained precise results for every test. We did not find anything, which stood out too much from the pattern except that the red plastic sheet, when used resulted more bubbles generally than the blue sheet. This shows that chlorophyll absorbs red light more easily than blue. We acquired similar results with each repetition and found ours to be similar to previous experiments. The Elodea produced more bubbles with sheets at each end of the spectrum because the chlorophyll in the plant absorbs all the colours but transmits green. When the light is absorbed the plant converts it into energy to photosynthesize. The more light energy it receives the better and faster it can do this so when the sheets near the blue and red parts of the spectrum are held in front of the Elodea it absorbs the light and can photosynthesize better. If plastic sheets are held up which are have a colour near the green part of the spectrum then the light will be transmitted and the plant will not be able to photosynthesize as well. In this experiment we have covered the main colours of the visible spectrum and they are sufficient to produce the results that we are looking for.
If we were to repeat the experiment then there are several ways we could improve it. For example to get around the problem of the heat from the lamp producing more bubbles then a thick glass panel could be placed in the middle to prevent any heat reaching the Elodea. To improve the accuracy of counting the bubbles, you we could only count the ones, which are a certain size, and only the ones coming from the very end of the Elodea. If there were lots of people counting the bubbles and the results averaged then that would be a more accurate way of obtaining the information necessary. To extend the investigation you could change certain variables for example the type of plant that you are using to count the bubbles from. You could try an entire species of plant and see if the results are similar for every type. You could use different chemicals in the water each time to see which chemicals result in the greatest rate of photosynthesis.
Evaluation
Overall, I would state the experiment as a success since my predictions were supported by my results. This is important in reflecting success only if my prediction was sensible and logical. Just as important is where the experiment was not a success and why. This photosynthesis investigation was probably not performed as accurately as it could have been due to some controllable and uncontrollable conditions. Some mistakes can be corrected.
While performing the experiment, the piece of pond weed did not photosynthesize at a steady rate, even when the temperature was kept almost constant. The second reading at 25C was far greater than the first reading at 25C. While the number of oxygen bubbles was being recorded, the rate at which the plant was photosynthesizing had increased several times. This may be due to the poor circulation of sodium hydrogen carbonate at the beginning of the experiment. Carbon dioxide may have initially limited the rate of photosynthesis. I had to repeat the first few temperature readings as they were so unequal, until finally they settled down.
The negative effects from this problem may be inaccurate data for some readings. These would show up on my graph. However, there seemed to be few anomalies than was expected when the experiment was being performed. Almost all readings were in correlation with each other.
A large factor in determining data accuracy is the amount of human error during experiments. The rate at which oxygen bubbles were being produced by my plant was so high that I found it difficult to count the amount of bubbles. I estimate a margin of error of at least 3 bubbles for each reading taken. To improve the accuracy of the results, the readings would have to be taken several more times. The entire experiment could have been performed again, and the new results could be combined if the same plant is used. But the photosynthetic rate of the same piece of pond weed would eventually decrease over time anyway. Repetitions would, however, improve the overall reliability of the results.
There are quite a few factors that could affect the results of my experiment. Some of these are variables that were mentioned earlier and could not be controlled, or they were variables that were not initially considered.
While performing the experiment, some of the oxygen produced from photosynthesis may have dissolved into the water. Some oxygen may have even been used by micro-organisms living on the pond weed. The amount of oxygen dissolved or used by microbes is probably insignificant to my results since the degree of accuracy at which I measured was not high enough. Some oxygen is also used during the respiration of the plant. But since only bubbles were counted, the volume of bubbles was not as important. But to volume of oxygen produced is important, since it was volume in terms of bubbles that were measured. As the rate of photosynthesis decreased due to a decrease/over increase in temperature the size of the bubbles produced also became smaller. This change in bubble size was no accounted for when the results were analyzed. For a more accurate analysis of the collected data, volume should have been measured instead of bubble quantity since the size of bubbles can vary. Using a capillary tube in place of the test tube so that the volume of each bubble could have been measured could have done this.
During the optimum temperature I had experienced counting difficulties of the bubbles being produced. There are also factors affecting accuracy at low temperatures, as the light I am using is vital for the plant to photosynthesise but it also gets extremely host and can heat the water. Although this temperature increase will be slow and insignificant it was still effecting my results and threfore not perfect.
Light intensity was also another factor that was controlled by the lamp being used; the lamp was fixed at a point as close to the beaker as possible to ensure maximum light intesity on the elodea.
The method of the experiment could probably also be improved to obtain more reliable results. As already mentioned, the a capillary tube should be used in place of a test tube to accurately measure the volume of the oxygen produced. Due to the high rates of photosynthesis of the pond weed, readings should be taken within shorter time periods. I had originally chosen to count the number of bubbles in 30 seconds but this produced miscounts in the readings. If during a repeated experiment, counting bubbles is still used, there is a smaller chance for human error when counting within a smaller time frame. If the capillary tube option was to be chosen, volume should be measured for a smaller time frame to reduce the overall time to complete the experiment. Also, during high rates of photosynthesis, it would still be difficult and impractical to measure the volume of oxygen produced for a long duration.
Due to the nature and convenience of the experiment, it could be easily modified to investigate another variable of photosynthesis. Since sodium hydrogen carbonate (NaHCO3) is used to provide the pondweed with carbon dioxide. Performing the experiment with different volumes of NaHCO3 could vary the amount of CO2. The plant would be kept at a constant distance from the lamp and a constant volume of water would be added to the sodium hydrogen carbonate.
