Method:
A shoot of Elodea plant was cut at the non-growing end and then put into a boiling tube with the cut end facing upwards. Pond water was then added to the boiling tube as well as some extra Co2. The boiling tube was then placed into a beaker of water. A metre ruler was placed onto the desk with 0 dead centre of the flask. A lamp was placed at distance x from the beaker. This distance was measure to the front part of the bulb head. This setup was left for 5 minutes to equibrate. Distance x was set and the number of bubbles released from the plant in 2 minutes was recorded. This was repeated 3 times from each distance to find the average.
Results:
See chart.
Other observations,
The bubbles coming of the leaf were big.
Some bubbles caught on a leaf above it, forming a bigger bubble which when rising to the surface only counted as one.
Evaluation:
My prediction is true; the rate of Photosynthesis does go up with the light, however thers is a dip. I think that this may be due to one of the factors that could have had an effect on the experiment.
The main factor was the size of the bubbles; they were large and did not rise at even time intervals (this would have suggested even volumes of gas) this also meant that fewer bubbles rose ad that made it less accurate. If I started the 2-minute count down as a bubble was just forming or as it was just about to rise it could change my result by a few bubbles. (quite a lot of gas considering the size of the bubble) this is why it would have been more effective to measure the volume of gas escaping my trapping it.
Other less important factors may have been a change in other lighting, for example the sun going in. For a more accurate study it should have only been one light source.
The amount of CO2 in the water must have decreased as the plant converted it to Oxygen. This may have affected its performance.
Conclusion:
Light intensity does effect the rate of Photosynthesis in a plant, however I think that the experiment could not quantify this rate because it was too inaccurate and had too many sources of error
