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Investigate the effect of changing light intensity on the rate of photosynthesis.

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Photosynthesis Coursework. Aim: To investigate the effect of changing light intensity on the rate of photosynthesis. Background: Photosynthesis is the manufacture by plants of carbohydrates and oxygen from carbon dioxide and water in the presence of chlorophyll with sunlight as the energy source. This chemical process occurs in the leaves, with glucose (carbohydrate) being the plants food source and oxygen the "waste" product. Photosynthesis is dependent on favourable temperature and moisture conditions as well as on the atmospheric carbon dioxide concentration. Increased levels of carbon dioxide can increase net photosynthesis in plants. The chlorophyll is used to convert light energy into chemical energy. Carbon Dioxide + Water + (energy from light) ? Glucose + oxygen 6Co2 + 6H20 + Light energy = (chlorophyll) = C6H1206 + 6H20 The factors that effect the rate of reaction are temperature light and the concentration of carbon dioxide. The temperature is important because if it is too cold, the rate of photosynthesis will be limited because the enzymes will not work properly. Light is essential because it drives the rate of reaction and carbon dioxide must be present to produce the glucose and 02 Prediction: I predict that the more intense the light, the faster photosynthesis will take place because light is needed for the reaction and there will be more input energy. When the lamp is at its highest wattage it will be giving all the light (energy) ...read more.


Repeat the procedure 3 times to make sure you have no anomalous results. Results: These are the results of the full photosynthesis investigation. Wattage Light energy (joules) Experiment 1 No. of bubbles after 6 minutes Experiment 2 No. of bubbles after 6 minutes Experiment 3 No. of bubbles after 6 minutes No. of bubbles after 6 minutes (average) No light 0 0 1 1 1 20w 72 00 3 8 5 5 40w 14 400 7 16 14 12 60w 21 600 49 44 50 48 100w 36 000 55 51 61 56 We didn't have an 80-watt light bulb so by plotting a graph we could extrapolate how much an 80-watt light bulb would affect the rate of reaction. We also worked out how much light energy was being given out. We did this using the formula: 1 watt = 1 joule of energy per second 40 watts = 40 joules per second To work out how much energy was spent it total, we times the number of watts by 60 to get one minute and then we multiplied it by 6 to work out the energy for 6 minutes. 100w x 60= 6000 = 1 min x 6 = 36 000 joules (6 mins) 60w x 60 = 3 600 = 1 min x 6 = 21 600 joules (6 mins) 40w x 60 = 2 400 = 1 min x 6 = 14 400 joules (6 mins) ...read more.


This could have been due to lack of attention on counting the bubbles. To improve the accuracy of counting the bubbles, we could have used a better container other than the beaker such as using test tubes to see more accurately. Measuring the light intensity could have been more accurate if we measured the distance between the light and beaker with more precision. Also breathing into the test tubes would have affected the experiment as you are letting out carbon dioxide. If we repeated the coursework then we would make sure to either not breathe by the pondweed or to wear masks. Also I could use a thermometer to check that the temperature of the water in each beaker is the same. At 80w we expect the results to be half way between 60w at 100w as that would be the likeliest thing to occur. Making sure there were no other factors affecting the rate of photosynthesis is very difficult, but if we were to make sure carbon dioxide was not interfering with the experiment, it would be a lot more accurate. To confirm that my conclusion is correct, I could repeat the experiment one more time to see if the results were similar. To continue the experiment I could use the other factors that affect the rate of photosynthesis instead of intensity of light. I would find a way to set up the experiment so I would keep the same light intensity (I would use a 40w bulb) and alter the temperature, by using water at different temperatures with the same amount of elodea. ...read more.

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