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Investigating the effect of Light Intensity on Elodea.

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Investigating the effect of Light Intensity on Elodea Aim: The aim of my experiment is to determine whether or not the intensity of light would affect the rate of photosynthesis in a plant. To do this I will place different pieces of Elodea (pondweed) into a beaker and expose it to varied light intensities, and observe the amount of oxygen given off by the plant. Introduction: Photosynthesis is the process of converting light energy into chemical energy and storing it in the bonds of sugar. Photosynthesis occurs only in the presence of light, and takes place in the chloroplasts of green plant cells. Photosynthesis can be defined as the production of simple sugars from carbon dioxide and water causing the release of sugar and oxygen. It is the chemical process, which takes place in every green plant to produce food in the form of glucose. Plants use the suns energy to join together water and carbon molecules to make the glucose, which is sent around the plant to provide food. Cells in the root or stem can use the glucose to make energy, if the plant does not need to use all the glucose immediately then it is stored as starch. It is possible to measure the rate of photosynthesis by counting how many bubbles or the volume of oxygen produced. In this experiment I will collect data to see if it supports my prediction. The following chemical equation summarises photosynthesis: Carbon dioxide + water glucose + oxygen CO2 + H2O C6H12O6 + O2 From this equation we can see that the photosynthesis reaction requires light. Light is a form of energy, and when it falls on the chloroplasts in the leaf, it is trapped by chlorophyll, which then makes the energy available for chemical reactions in the plant. As the amount of light (energy) falling on the plant increases, the more energy chlorophyll can trap, so more energy is available for chemical reactions, so more photosynthesis can take place in a given time. ...read more.


The angle should be the same, so that the test is fair, a bigger opening would let out more bubbles than a smaller opening. 4. This process should be done under water so that air bubbles aren't trapped in the ends of the Elodea. It should be done carefully with a scalpel on tile, cutting away from your body. 5. Place one length of Elodea into the measuring cylinder. 6. Close the blinds and turn off all the lights. 7. Place the lamp at a measured distance from the Elodea (using a 1m ruler). E.g. start the experiment with a distance of 50cm from the Elodea. Set up a lamp at a set distance from the plant, ensuring that this distance is from the filament of the lamp to the actual pondweed, rather than the edge of the beaker. 8. Turn the lamp on, and give the Elodea about 2min to adjust to this light intensity. Then time with a stop watch and count how many bubbles are produced in 1min at that light intensity. Repeat at the same light intensity for a second and third time and record results. 9. Repeat the experiment at the following distances: 50, 45, 40, 35, 30, 25, 20, 15, 10, 5cm from the plant. 10. Repeat the whole experiment using 2 more pieces of Elodea. 11. Record all results into a table, and graphs. The graphs are useful to see patterns in data. Results: Table to show how many bubbles produced by the plant within a minute at several distances (light intensities) 5cm 60 64 67 65 63 64 10cm 49 51 50 53 49 49 15cm 38 39 40 39 39 38 20cm 35 36 34 33 34 35 25cm 29 30 30 28 30 29 30cm 25 25 26 24 27 26 35cm 23 24 23 22 23 23 40cm 19 21 19 20 20 20 45cm 17 18 16 17 19 16 50cm 11 13 10 12 15 14 5cm: 64 10cm: 50 15cm: ...read more.


Limitations: whether light was the limiting factor in the experiment. My prediction of light intensity no longer being a limiting factor could not be investigated, as a distance of zero cm could not be investigated. However, different light bulbs of various intensity's could have been used to investigate this prediction. A bulb of greater intensity could have been used to calculate where the graph levels of due to other limiting factors. Reliability of Evidence: The evidence cannot be taken to support a firm conclusion as the test was not very reliable due to equipment and method used. In my opinion, the experiment was not repeated enough times as the results seemed to be quite different from each other, and I was unsure of which results were anomalous. In my opinion, if I had obtained a mode result then I would be more able to support a conclusion. In my prediction I wrote that as light intensity increases, so would the rate of photosynthesis at a proportional rate. My results can support this prediction, although not prove the fact that the rate increases proportionally because my results are not reliable enough. My results cannot support the prediction that the rate of reaction will level off when light is no longer a limiting factor, because I did not increase the light intensity enough for it to no longer be a limiting factor. My results did form a curve, which supports the notion that light intensity is inversely proportional to the distance squared because the light energy spreads out as it travels further from its source. To further investigate: * A wider range of light intensities- to observe when light is no longer the limiting factor. This would have to be done by using brighter light bulbs. * How different coloured lights affect the rate of photosynthesis. * Experiment on a wider range of plants, observing patterns and trends. * Investigate how carbon dioxide affects the rate of photosynthesis. * Investigate how the availability of water affects the rate of photosynthesis. * Investigate how temperature affects the rate of photosynthesis. ...read more.

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