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Photosynthesis and colour of light

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Photosynthesis and colour of light PROBLEM I have been asked to investigate the link between wavelength of light and rate of photosynthesis. HYPOTHESIS I predict that the order of best absorption in a plat to produce more bubbles will be blue, yellow, orange, red and finally green. I predict this because blue has the shortest wavelength which produces the most energy and there is slightly higher absorption in the blue region by the plant. The red has the largest wavelength in the visible spectrum which produces the least energy. The reason why green is at the bottom of the list of absorption in a plant is because green is reflected off the plant and not absorbed as much as the others. It is reflected of the plant to be seen as green in our eyes. SCIENTIFIC KNOWLEDGE The spectral quality or colour of light is associated with its wavelength. Blue light has a shorter wavelength and higher frequency than red light. A simple table that indicates the wavelengths of colours in the visible spectrum is shown below. Wavelength (nm) Colour of light 400 Violet Indigo Blue 500 Green Yellow 600 Orange Red 700 In photosynthetic plants the pigments are very important. They absorb light energy and enable it to be converted into chemical energy which is used by the plants to make glucose and oxygen from carbon dioxide and water. ...read more.


Red algae, which tend to be found at even greater depths, contain more pigments to absorb the blue light which penetrates deeper into the water. It is the combination of pigments in a plant which determines which wavelengths of light can be utilised in photosynthesis. No plant absorbs light with equal effectiveness across the visible spectrum. This is why different colours of light may affect photosynthesis and the subsequent growth of plants. EQUIPMENT The equipment that I used was: * Elodea * Lamp * Beaker * Plasticine * Syringe * Ruler - measure the distance between the lamp and the plant * Timer - measure time * Sodium hydrogen carbonate METHOD Firstly I collected the equipment and set it up. We then filled the beaker with 400ml of 2% sodium hydrogen carbonate. To this we added the elodea and placed the beaker 50 cm away from the lamp. We then placed a coloured filter and placed it in front of the lamp. We left the plant there for 2 minutes (acclimatise to the conditions), and then placed the syringe over the plant. We decided that we would measure the volume of gas evolved from the plant during a 5-minute period. We then repeated using the same colour to ensure that our results are accurate. ...read more.


EVALUATING In the table, the results show that I have consistent results. Although they are consistent I do not think they are very accurate. In hypothesis I said that blue would be the most absorbed as it has the most energy to produce more oxygen. But as seen in the graph and results table, it only has the second highest bubble rate. Another strange result that I had was that green did not have the lowest bubble rate. I would have expected green to have the lowest bubble rate as the plant was also green, meaning that the green light should have been reflected back by the plant. However this could be because of a number of reasons, the shade of green that the filter was could have been a different shade to that of the plant. I could do more experiments for this investigation, as there are two more things that can be varied to change the release of oxygen in the plant. The two other factors are the amount of carbon dioxide added and water added. I could also vary the intensity of light on the plant to change the amount of oxygen released. This coursework As a conclusion to this experiment I think my results were good enough to say that they fitted my hypothesis and that with a little more precaution I could have proved my hypothesis completely correct. Sean O'Sullivan ...read more.

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