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An Investigation on the effects of Light Intensity on Photosynthesis

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An Investigation on the effects of Light Intensity on Photosynthesis Plan I plan to investigate how light intensity affects the rate of photosynthesis in pondweed. The rate of photosynthesis will be measured by the number of bubbles given off (considering that oxygen is produced as a waste gas during photosynthesis). The light intensity is measured by the distance between the lamp and pondweed. Fair test: Fix: the amount of pondweed, the amount of water and sodium hydrogen carbonate solution in the test tube, the time allowed for each experiment Change: the distance from the lamp to the pondweed (light intensity) Measure: the number of bubbles given off by the pondweed, the temperature of the water bath Variables: The following are factors that affect the rate of photosynthesis: Light - quality and quantity Carbon dioxide Temperature Water Chlorophyll Light is needed to provide the energy for the reaction to take place because it is an endothermic reaction. This is the variable that I am going to change, the light intensity will be measured by the distance from the lamp to the pondweed. The quality of the light will be kept the same because the same lamp will be used. Carbon dioxide is needed because the element are needed to produce glucose which is what the plant is trying to make. This can be controlled by having a fixed amount of sodium hydrogen carbonate solution in the test tube. ...read more.


The whole process was done again but the light was 20cm away, then 30cm, 40cm, 50cm and finally 60cm. Theory: In order for photosynthesis to happen light is needed. The more sunlight there is then the more the plant will photosynthesise because the light is the input energy put into the process (it is transformed into chemical energy). The reaction is endothermic so light is needed. But there comes a point where more light does not make any difference to the rate of photosynthesis because the light is at the light saturation point and photosynthesis occurs at the same speed even with more light because it has reached the optimum amount. The rate of photosynthesis cannot speed up because there is only a certain number of chloroplasts containing a limiting amount of chlorophyll and this can only absorb a certain amount of light. The rate of reaction to the light intensity is inversely proportional 1/d2. Prediction: I predict that the closer the lamp is to pondweed the faster photosynthesis will take place because light is needed for the reaction and there will be more input energy. The rate of photosynthesis to the light intensity is inversely proportional so it will increase rapidly at first but will not increases so rapidly when the lamp gets closer to the pondweed. When the lamp gets close to the pondweed the lamp will be giving all the light (energy) that the pondweed will need to photosynthesise at its optimum speed. ...read more.


hydrogen carbonate solution may have ran out a little, the light intensity might have changed a bit because of the varying sunlight coming in the windows. The sunlight could have been controlled by closing the blinds on the windows. The temperature could have been controlled better by having a bigger water bath. The method of counting bubbles was probably not very accurate because the bubbles can be of different sizes, this can be improved by leaving the plant to photosynthesise for longer and then the volume of oxygen given off can be measured. The experiment will be done as follows. If I had more time to do the experiment I would have done more repeats to get more accurate results and I would have done more experiments with the light intensity at 100 - 400 because this would have improved the line on my graph. This would have given more evidence which would give me a better idea of where to draw the line of best fit. My evidence is sufficient enough to support my conclusion and it agrees with my theory so they must be quite accurate. To extend my investigation to obtain additional evidence I could use more sophisticated equipment like a photosynthometer to measure the rate of photosynthesis. I could also change one of the other variables such as temperature: I would do the same experiment except the lamp would be kept in the same place and the water bath would be gently heated at different temperatures. ?? ?? ?? ?? James Robertson 10S ...read more.

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