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Photosynthesis is the process plants use to make their food.

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PLANNING Introduction: Photosynthesis is the process plants use to make their food. This occurs when plants take in sunlight energy and water (intake by the roots from the soil - especially when it has rained) and carbon dioxide. The energy from the sun is absorbed and then stored by the chlorophyll to make the carbon dioxide and water react together to make glucose and oxygen. The word formula is: Carbon dioxide + water --> glucose + oxygen And the chemical formula is: --> This is what we will be experimenting on: The rate of photosynthesis according to how much light (intensity) is applied from various distances. To measure this, we will be counting bubbles and taking readings. Aim: My aim is to investigate the effect of changing light intensity on the rate of photosynthesis and to show that oxygen is produced during photosynthesis. (We will be measuring this by counting the bubbles produced after a set amount of time.) Apparatus list * 1 piece of weed (elodea) * 0.25g of NaHCO (sodium hydrogen carbonate) * 250ml of H O (water) * a graduated measuring cylinder * a lamp (caution: HOT!) * a razor * tin foil/black paper * a stop clock * a metre ruler * a paperclip Prediction: When there is more light applied to the selected plant instead of a whole group of plant, the individual plant can use more energy. The more energy there is, the more can be used to make the carbon dioxide and water react together to produce glucose and oxygen; therefore the whole process speeds up when the light intensity is higher. ...read more.


Results: Distance from elodea (cm) Reading 1 (0.2% vol) Reading 2 (0.4% vol) 1st Reading 2nd Reading Average no. bubbles p/min 1st Reading Average no. bubbles p/min 10 372 396 76.8 399 79.8 20 274 257 53.1 262 52.4 30 228 219 44.7 209 41.8 40 185 177 36.2 159 31.8 50 150 148 29.8 135 27 The readings in the above table show the amount of bubbles after 5 minutes. From this table I was able to calculate the light intensity, which would be to divide 1 by the distance squared and then say for example the distance is 10cm, it would be 0.01 so, to write that in standard form would be 100 x 10 so that would be the light intensity for the light applied at a distance of 10cm away from the elodea. This will help me to plot a graph showing light intensity at different distances. To show this for all 5 distances, I have decided to put it in a table to show light intensity. Distance Light intensity 10 0.01 100 x 10 20 0.0025 25 x 10 30 0.0011 11 x 10 40 0.000625 6.25 x 10 50 0.0004 4 x 10 Graph(s): See graph paper. Observing: At the beginning, the average number of bubbles per minute for the 0.2% solution did not differ greatly from that of the 0.4% solution (76.8 and 79) and therefore the end result being 29.8 and 27. This is probably why, visually, the graphs look similar, because all of the graphs look extremely similar with trend, pattern and size. ...read more.


Accurate and reliable results? I think that a large proportion of my results are accurate, therefore are reliable but the anomalous results suggest that somewhere I have gone wrong with timing or maybe I miscounted the bubbles at some point e.g. at 30cm on the 1st reading of the 0.2% solution. However, the number of bubbles could have increased at some point more dramatically because of a rise in temperature on the outside (room temperature) causing the rate of photosynthesis to become unbalanced. I cannot see any anomalous results that are really far off the mark other than that of the reading for 20cm on the 2nd reading of the 0.2% solution. This indicates that my results are reliable. The experiment was difficult to complete because there was so much to do and find out and I think I probably could have spent hours doing more of it because no matter how much or how little you did, there was always something else you could do (e.g. change the temperature of the solution, the pH of the solution, the concentration - % - of the solution and so on), and I would have liked to be able to experiment a bit more, given the time. Possibilities for other experiments include using the concept and basics of this experiment but changing the NaHCO2 to something other like potassium hydroxide solution perhaps. Maybe we could use a plant under conditions in which we could measure the amount of carbon dioxide (CO2) taken in and the amount of oxygen given off and compare the two to see what kind of difference there is and why. 6 8 ...read more.

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