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The aim of the experiment is to determine whether the intensity of light would affect the rate of photosynthesis in a plant. You will know whether or not it does by counting the number of bubbles.

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Katie Garford Background Information Photosynthesis is the process where plants produce their own food. They are self-sufficient. Plants change carbon dioxide and water to make glucose and oxygen. This does not happen without light energy and chlorophyll. Without light energy and chlorophyll carbonic acid would be produced. Light provides the energy for photosynthesis to happen and chlorophyll is an enzyme which speeds up the reaction. Oxygen is a bi-product of photosynthesis and is released into the atmosphere. Glucose is used for biomass and energy or it can be stored as starch. The equation for photosynthesis is: light energy carbon dioxide + water glucose + oxygen. chlorophyll 6CO2 + 6H20 C6H1206 + 602 The temperature, intensity of the light, water supply and carbon dioxide supply all have an effect on how efficiently plants convert the raw materials into the food that they need. To prove that chlorophyll was required for photosynthesis I did two experiments. First of all I tested variegated leaves for starch. When you put iodine on the leaf, the white areas will contain no chlorophyll whereas everywhere else will. You could also put one plant in darkness for 12 hours and another one in light for 12 hours. After that time you test for starch using iodine and the leaf in the dark would turn yellow as it wouldn't contain starch because it hadn't photosynthesised. ...read more.


Prediction I predict that the more intense the light, the higher the rate of photosynthesis. I think this because plants rely on light for photosynthesis and so therefore if the light is not very intense not so many bubbles of oxygen will be produced. As the light is moved away the intensity of the light is reduced and the number of bubbles will decrease steadily. For example, at 25cm away the number of bubbles may be 25 so you would expect the number of bubbles at 50cm away to be 50cm as the light intensity is decreased. I think that no bubbles or very few will be produced at 100cm away from the light. I think the same results will follow for the strength of light. As the strength of light decreases the amount of bubbles will also decrease. Results These results are from the first set of experiments. Voltage(W) 100 100 100 100 100 Distance(cm) 0 25 50 75 100 Bubbles/min. 17 12 7 5 4 Voltage(W) 60 60 60 60 60 Distance(cm) 0 25 50 75 100 Bubbles/min. 17 6 5 3 1 Voltage(W) 40 40 40 40 40 Distance(cm) 0 25 50 75 100 Bubbles/min. 12 3 0 0 0 These results are from the repeat experiment. Voltage(W) 100 100 100 100 100 Distance(cm) 0 25 50 75 100 Bubbles/min. ...read more.


Perfect results could never be achieved as living things do not work at a constant rate. For more accuracy the results could be taken over a period of time, say 4 weeks. This way you would achieve results from when the pondweed is working at different rates. The method used for measuring the number of bubbles wasn't very accurate as counting bubbles can get very boring and miscounting could be a common mistake made and could easily explain anomalous results. Another reason why anomalous data may have been collected is the possibility that the piece of pondweed was damaged. It may have got too hot which would have denatured the chlorophyll and this would affect the rate of photosynthesis as chlorophyll is required for photosynthesis to occur. To overcome this problem you could change the piece of pondweed after each set of results was taken or you could leave a set amount of time after each set of results was collected for the pondweed to cool down. If I was to do this experiment in the future then I would use different light filters to change the colour of the light. By doing this I would find out if the plant prefers to absorb certain colours over others. For example, does chlorophyll prefer green as it is green itself. To do this I would use the same set up as I did for this experiment but the distance and light voltage would stay the same whereas the light filters would change in order to get different colours. ...read more.

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