Pond Weed Investigation

The effect of temperature on the rate of photosynthesis in Canadian Pondweed Elodea sp.

In this investigation I plan to investigate how temperature effects the rate of photosynthesis in Canadian pond weed, this will be achieved by comparing the amount of oxygen produced by the pondweed at different temperatures.
It will be a fair test and my only independent variable will be the different temperatures of water the pondweed will be submerged in. I am choosing different temperatures as my independent variable because I know from past experiments that different temperatures affect the enzyme activity and therefore the rate of photosynthesis. This experiment is also the most straightforward to set up and carry out, this means that extra time will be available to spend on repeats and extremely accurate results. All other factors of the experiment remain constant; the weight of pond weed, the light density, the colour of the light, the method of collecting the results (measuring the volume of displaced water in an upturned measuring tube) and the acclimation time of 2 minutes. The dependent variable is the volume of oxygen produced by the pondweed, this is measured by the amount of water displaced in an upturned measuring tube. The volume of oxygen produced is directly proportional to the rate of photosynthesis, so having worked out the rate I can compare the different temperatures.
First I will set up the apparatus, this consists of: a water bath at 20°c, in this bath is a fermenting tube with the sample of pondweed inside and 20cm3 of water. The delivery tubing leads to another water container and to an upturned measuring tube.
I leave the pondweed to photosynthesise for two minutes and then record the level of the water in the measuring tube, the pondweed is needed to be left for the two minute period to allow it to start functioning at the temperature. I then leave the pondweed to respire for three minutes, after this time I aga…

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