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Investigation into the colour of light needed to start a photosynthesis reaction

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Introduction

Investigation into the colour of light needed to start a photosynthesis reaction Diagrams Method The apparatus for this experiment will be setup as shown in the diagram, for all the experiments the coloured filter will be 5cm away from the white light bulb, which is a 60watt bulb, and the beaker will be 20cm away from the edge of the coloured filter. Just before the experiment takes place we will place the pond weed (which has been in darkness for at least 24 hours to stop it any photosynthesis) into the beaker. I will then place the funnel over the pond weed and place the test-tube into the beaker (like the diagram above) I will then fill the beaker up with cold tap water till it covers the bottom of the test tube (450ml). This is so that we can easily count the oxygen bubbles as they come off the pond weed. Now that the experiment is ready to start, I will turn on the light for one minute, then after the first minute I will count how many oxygen bubbles come from the pond weed in the second minute. I will repeat this stage again once 10 minutes has passed. ...read more.

Middle

From these results I have found that violet light is the most absorbed by the pond weed and that green light is the lease absorbed and most reflected, unused colour. I think my results support my prediction, apart from the bit where I thought that green light would not allow the pond weed to photosynthesise and create oxygen bubbles. Evaluation Overall, I think my experiment went well, but I did notice that sometimes the accuracy was not as good as it should be. This was show by the size of our error bars, which do not give a very clear sign of the exact result. This was due to the fact that I was depending on the oxygen bubbles been the same size, which they visibly wasn't, this experiment wasn't very successful scientifically because there was not enough detail about the oxygen bubbles, the quality of the filters or the energy of the light coming through the filters. I think this error margin shown by the error bars could have been reduced if I had repeated the experiment more and taken an average. There are also a number of smaller inaccuracies which apply to both the preliminary experiment and the main experiment. ...read more.

Conclusion

Another point is that I would use more accurate measuring techniques which I said before in this evaluation if I were to repeat this experiment again. One of the things which struck me most was that violet light made the pondweed give off many more oxygen bubbles than any other colour, so a good idea for if the experiment was repeated again would be to use ultra violet energy to see if the trend with violet light continued. I think another improvement to my tests would be an extension on the amount of time each test lasted, because I don't really think I gave the pondweed enough time to "get going" - this was a constraint on me though, because I did not have enough school time to do the experiment as long as I wished. Another idea I would like to try if I repeated the experiment is whether light from different light sources combined with different colours has different effects on the rate of photosynthesis by the pondweed. I could try light from fluorescent or halogen sources along with coloured light filters. ?? ?? ?? ?? Adrian Hall Adrian Hall - Centre No#: 44171 - Candidate No#: 0268 ...read more.

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