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# Investigating the rate of photosynthesis in pondweed.

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Introduction

Investigating the rate of photosynthesis in pondweed Possible variables and preliminary work Variable High Explained Low Light intensity 9 mm3/min of O2 I found that changing the light intensity was good as it gave good results. 7.5 mm3/min of O2 CO2 concentration 10 mm3/min of O2 I found that concentration gave a good range of results and it would also be interesting to investigate this one. 5.8 mm3/min of O2 Temperature 8.3 mm3/min of O2 Temperature gave a small range of results and is unreliable as the temperature would always be changing. 8.4 mm3/min of O2 Volume of water 8.6 mm3/min of O2 The volume of water did not give a good range of results. 7.9 mm3/min of O2 Chosen Variable My chosen variable is concentration of CO2 because it gave me a good range of results and it is a main factor of photosynthesis. Fair Testing To keep this a fair test I will change only my chosen variable and keep all other variables the same. ...read more.

Middle

using light absorbed by chlorophyll. Here is the formula for photosynthesis: Carbon Dioxide + Water Sunlight Energy + Oxygen 6CO� H�O C6H12O6 6O� In this experiment the NaHCO� increases the amount of carbon dioxide in the solution. Therefore more carbon dioxide molecules diffuse into the plant than before the NaHCO� was added. The CO� molecules pass through the plant's pores, letting the plant photosynthesise at a higher rate. I expect the graph to look like this. 1. This part shows that as the CO� increases so does the rate of photosynthesis. 2. This part shows that it tails off. This is caused by limiting factors. There are 4 things needed for photosynthesis to occur. They are light, chlorophyll, water and CO�. At any given time one other of the above factors will become the limiting factor that keeps photosynthesis at that rate. If the CO� increases then it will cause the photosynthesis will increase until a point. ...read more.

Conclusion

Overall the results obtained were of good quality. The procedure was a good one although there are some things that could be changed. The bulb was probably heating the water slightly therefore not keeping all the variables the same this could be improved by having the bulb further away from the beaker. The results however were not changed greatly by this and therefore were suitable to support the conclusion. To provide additional evidence experiments on the other factors of light and heat could be investigated. These would show a similar graph shape proving again that these limiting factors stop the rate of photosynthesis increasing any further. This would be done by setting up this same experiment but keeping the sodium hydrogen carbonate level the same and moving the light nearer or closer to the beaker to measure light intensity would be one. The other would be to change the temperature of the water for each result. However if the temperature was increased too much it would be found that it would destroy the chlorophyll enzymes preventing photosynthesis occurring further. ...read more.

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