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How does light intensity affect the rate of photosynthesis of Canadian Pondweed?

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Step - By - Step Plan Firstly I will get all my equipment out and place it on my working place. Secondly I will turn out all the lights and pull down all the blinds (if there are any) so that I will be able to get maximum light intensity from my lamp to the pondweed and keep it a fair test as my pondweed is only getting the light from the lamp and from no where else. Then I will measure 10cm of pondweed and place it into my glass beaker and place my glass funnel over the pondweed as you can see in the following diagram: Next I will fill my glass beaker with water up to about half way then add my hydrogencarbonate indicator (to keep the amount of CO2 the same each time), after I have done that I will fill the glass beaker to the top with water, next I will get my straw and place it in the beaker filled with water and blow until it goes a yellow colour, this is about a blow for 5 seconds. After that I will get my test tube and fill it to its peak with water and put my thumb over it making sure I don't spill in water, I will carefully put it over the top of the funnel without losing any water (it is essential that you don't lose any water because if you do, each time you carry out the experiment there will be different amounts of water and it will not be a fair test) ...read more.


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. It cannot photosynthesise any faster 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 which is called the light saturation point but if the light intensity is to high then it could bleach the chlorophyll and delay photosynthesis. The other limiting factors should be at their optimum or remain constant throughout the experiment and so should not affect the experiment. So overall I think that the most oxygen bubbles given off will be when the lamp is 10cm away from the pondweed because it is not to close and therefore wont bleach the chlorophyll and delay the rate of photosynthesis, I think it is the ideal distance. When the lamp is 20cm and 30cm away from the pondweed they will be relatively similar results and a difference of approximately 20 air bubbles. It will give off the least oxygen bubbles when the lamp is 40cm away from the pondweed because the further the lamp gets away from the pondweed the harder it is for the chlorophyll to absorb the light so it will take longer to photosynthesise. ...read more.


My line of best fit did not suit some of my results because I had anomalous results as a result of this. I may have had anomalous results because some of the factors were limiting by the time. Something or a factor was limiting. I would suggest that it was the temperature because it could have got too low and slowed the rate of photosynthesis or maybe the concentration of the carbon dioxide would explain the amount of anomalous results. The evidence is just about sufficient enough to support a firm conclusion because about half of the results are nearly accurate, although some are anomalous when drawing a line of best fit. Some results that were plotted are in one place and some scatter off on the graph which prove that they are anomalous and something was not accurate during the experiment such as a factor that was limiting. Evidence is sufficient as a clear pattern is discovered that this is because the rate of photosynthesis slows down and ultimately this supports this firm conclusion. The improvements I would make for further work is to allow my results to be even more accurate and fair and much more reliable, but trying to avoid anomalous results when obtaining evidence and analysing evidence. I would like to provide additional evidence for the conclusion by extending the results and making more justifications and using scientific knowledge for more key factors that could be tested which I would like to investigate and test on with this similar method. ...read more.

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