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Experiment to test whether light intensity affects the rate of photosynthesis.

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Introduction

Experiment to test whether light intensity affects the rate of photosynthesis. Introduction: Photosynthesis is the process by which green plants and certain other organisms transform light energy into chemical energy. During photosynthesis in green plants, light energy is captured and used to convert water, carbon dioxide, and minerals into oxygen, sugar and other, energy-rich, organic compounds. Photosynthesis can be indicated by the following equations: Carbon Dioxide + Water Sugar + Oxygen CO2 + H2O C6H 12O 6 + O 2 Or: Light CO2 + 2H2O (CH 2O) + O 2 + H2O Green plants Photosynthesis is incredibly important in the maintenance of life on Earth. If photosynthesis ceased, there would soon be little food or other organic matter on Earth. Most organisms would disappear, and in time the Earth's atmosphere would become nearly empty of the gas oxygen. The only organisms able to exist under such conditions would be the chemosynthetic bacteria, which can apply the chemical energy of certain inorganic compounds and thus are not dependent on the conversion of light energy. The rate of photosynthesis is defined in terms of the rate of oxygen production either per unit mass (or area) of green plant tissues or per unit weight of total chlorophyll. In this case we are measuring the amount of gas collected in the syringe in milliliters (ml). ...read more.

Middle

3. Each test will consist of five measurements. For each measurement the lamp will be 10cms further away from the plant (up to 50cms because the light will not photosynthesise beyond that). 4. To make it a fair test we will keep everything constant except the light intensity (the distance of the lamp from the plant). 5. To keep the carbon dioxide levels the same we will put 1% bicarbonate in the water because it produces CO2. 6. Also we will keep the temperature of the water in the beaker at about 20 - 30�C. Each measurement will last 3 minutes and there will be a rest of about 2 minutes after each one so the plant recognises the change in light intensity. 7. We will keep a table of results for each test we do and we will do more than one test to increase accuracy. 8. Finally we will draw a graph and write an evaluation. Safety: We will make sure our apparatus are out of the way of other people so that they will not be knocked over. Fair test/Accuracy: In order to conduct a fair test we will make sure we keep everything that we are not testing constant. Results: Test number Distance of lamp from plant/cm (D) Start /ml Finish /ml Difference /ml 1_ D2 1 10 0.56 0.65 0.09 0.01 20 0.68 0.74 0.06 0.0025 30 0.75 0.79 0.04 0.0011111 40 ...read more.

Conclusion

We could have weighed the pond weed and measured the length etc. * The temperature of the water was checked but not very accurately. * Adding bicarbonate controlled the CO2 levels but we don't know if those levels were the same every time. * The water supply was also not checked to see whether there were any impurities and that it was obtained from the same source. * The availability of minerals is the last factor that was not kept constant. * We did not give the plants any more minerals than they already had and we did not measure how much they started with. * If I could do the experiment again I would want to try different ways of testing that light affects the rate of photosynthesis. For example I would put different coloured filters over the lamp to see what colours the plant photosynthesises in faster. I could also do the experiment again only this time changing things like the CO2 levels, the plant type or whether it is flowering, the level of minerals and others like those mentioned above. To conclude I would say that the rate of photosynthesis is directly proportional to the light intensity. I would say this because the graphs that I have drawn follow the same pattern where, as the light intensity decreases, so does the amount of oxygen produced. Tom Gerrard Biology - Mr Marsh 13/09/02 10Si - 1 - ...read more.

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