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Rates of photosynthesis

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Verity Kennedy 11I Rates of photosynthesis For this experiment we will be finding out how light affects the rate of photosynthesis. To do this we will fill a beaker with water and add some Canadian pondweed. Then we will place a funnel over the pondweed to prevent any gas escaping, then place a measuring cylinder over the funnel to measuring the amount of water displaced by the gas. This will determine the rate at which the plant photosynthesises. We will change the intensity of the light to see if this affects the experiment. Before we started the experiment we carried out a computer simulation of the experiment. We set the program to a certain amount of light the plant received and recorded the results, the temperature was set for 20 degrees and the amount of calcium chloride was set for 3%. These are the results for the light experiment that was done by computer simulation: - Light experiment Light distance (m) 0 10 20 30 40 50 60 70 80 90 Volume of oxygen (mm2) 0 8 16 25 33 42 50 58 67 75 Safety As this experiment isn't very dangerous there is no need to take heavy precautions, but we should always: - * Wear goggles * Put bags and coats out of the way so it isn't a hazard to other pupils * Keep the experiment away from the side of the bench in case ...read more.


The graph from the computer simulation shows me that the line for the amount of oxygen produced gets steeper when the amount of light is more intense. This determines that as the light intensity gets higher the more water is displaced, this is because the light is changing carbon dioxide and water into glucose and oxygen by a chemical process. Oxygen is the visible product of the equation, because the oxygen displaces the water. The closer the light the more energy absorbed by the plant, so as the rate of photosynthesis increases the more oxygen is release. Table of Results Experiment 1 Distance of light (m) Amount of water (ml) Number of bubbles Temperature (c ) Time (min) 100 1 140 20 2 80 1 229 20 2 60 1 299 20 2 40 1 400 20 2 20 1 580 20 2 0 1 >600 20 2 Experiment 2 Distance of light (m) Amount of water (ml) Number of bubbles Temperature (c ) Time (min) 100 1 137 20 2 80 1 228 20 2 60 1 260 20 2 40 1 450 20 2 20 1 660 20 2 0 1 >700 21 2 Experiment 3 Distance of light (m) Amount of water (ml) Number of bubbles Temperature (c ) Time (min) 100 1 198 20 2 80 1 250 20 2 60 1 262 20 2 40 1 390 20 2 20 1 612 20 2 0 1 >650 20 2 Average Results Distance of light (m) ...read more.


* Carbon dioxide There could have been carbon dioxide already present in the water, which would have given the plant more carbon dioxide; this would have made the plant produce more oxygen. The pondweed may have been already photosynthesising before the experiment, because of the small amount of carbon dioxide already in the water, which would have made our results higher than they should have been. The amount of water wasn't a problem because the pondweed is used to being situated in a high depth of water or a low depth of water. We could have prevented the changes in temperature by keeping the pondweed in a fridge where it is cold and dark. This would have reduced the chance of the plant photosynthesising to a minimum. The enzymes in the plant would have been in a dormant state. Overall I am happy with the experiment. This experiment is the best way to study rate of photosynthesis I know that it would be quite have to change it much. If I were to do the experiment again I think the main improvement should have been the time. I think that it should have been extended so that our results where more accurate. We could have studied the plant photosynthesising for longer. This would be easy to change and if I were to do the experiment again I would time each light distance for 5 minutes. If I did this maybe the water would displace more so that I could include it more in my evaluation and analysis. ...read more.

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