The effects of light intensity on the rate of photosynthesis in Elodea.
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The effects of light intensity on the rate of photosynthesis in Elodea Aim I aim to investigate the effects of the quantity of light and thus the light intensity on the rate of photosynthesis in Elodea. Background Photosynthesis is the production of food compounds from carbon dioxide and water by green plants using energy from sunlight, absorbed by chlorophyll ie. Photosynthesis is how plants feed. lightlightlil 6CO2 + 6H2O à C6H12O6 + 6O2 Raw materials Products ie. Green plants make organic substances from inorganic substances. In order to keep the equation for photosynthesis simple, glucose is shown as the only food compound produced. However, this does not mean that glucose is not the only food compound produced. The process of taking in and giving out gases is known as gaseous exchange. When green plants photosynthesise, they take in CO2 and give out O2. This only happens in daylight when light is available as an energy supply. The exchange of gases in green plants in light is the opposite of that of animals; however this does not mean that green plants do not respire. During daylight, plants photosynthesise and respire at the same time, hence all CO2 produced by the plant during respiration is transformed into O2 and food (and thus energy) for the plant. It is only when the rate of photosynthesis is greater than the rate of respiration that CO2 will be taken in and excess O2 given out. ie.
Also, the weight must not cover the very tip of specimen, the meristem; this tip of the plant is where the plant is growing the most, and thus photosynthesising the most. The end of the plant should be cut at an angle, in order to release CO2 most effectively. The thermometer monitors the temperature of the water bath, thus checking whether or not there is a temperature increase or decrease, resulting in the change in the rate of p/s in the Elodea specimen. A change in the temperature would prevent the investigation from being a fair test. Hence, maintaining a constant temperature and CO2 level maintains a fair test, with only one variable changing - the LI. Counting the number of bubbles produced by the Elodea would be a fairly reliable way of measuring the CO2 produced. Obviously affixing a gas syringe to the top of the boiling tube would be far more reliable, but I doubt that there would be a sufficient volume of CO2 in a short time (max 3 mins) produced to make a considerable difference when reading the volume of gas produced by the Elodea specimen. By counting the number of bubbles, we are assured of a sufficiently large reading. The Elodea must be left for a sufficient amount of time for it to adjust to the new LI; I believe that five minutes should be ample enough - this will be consolidated by the preliminary results.
The planned procedure worked fairly well, needing only a few minor adjustments to obtain good results. The evidence obtained supports photosynthetic theory and my prediction; it appears to be sound. As mentioned before, the only (slightly) anomalous result is simple to explain; Elodea, being a living organism will not produce uniform results - thus the anomaly, it can be said, is due to the fallibility of the specimen. No problems were encountered; the only circumstance which would have been a difficulty would have been controlling the temperature. However, this was eliminated by putting the boiling tube into a water bath which absorbed the majority of the heat energy from the lamp, and by keeping the specimen far away enough from the lamp for there to be no significant change in temperature. This experiment is rather crude, and the method of measuring the rate of photosynthesis especially; counting the number of bubble of CO2 produced in a minute is not very accurate - measuring a volume would be far more precise, but the time for a reasonable amount of CO2 to be produced would be rather long, I feel; this would be inappropriate I believe, where time is limited. Further work could be carried out, investigating the effects of the quality of light on the rate of photosynthesis; different coloured light for example could be used. This could be of commercial benefit, as finding out the effect of the colour of light on the rate of photosynthesis could aid plant growers to find out which type(s) of light make(s) plants grow quickest.
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