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Introduction

What is Photosynthesis? Process by which green plants trap light energy from the Sun. This energy is used to drive a series of chemical reactions, which lead to the formation of carbohydrates. The carbohydrates occur in the form of simple sugar, or glucose, which provides the basic food for both plants and animals. For photosynthesis to occur, the plant must possess chlorophyll and must have a supply of carbon dioxide and water. Photosynthesis takes place inside chloroplasts, which are found mainly in the leaf cells of plant. The by - product of photosynthesis, oxygen, is of great importance to all living organisms, and virtually all atmospheric oxygen has originated by photosynthesis. Chloroplasts contain the enzymes and chlorophyll necessary for photosynthesis, and the leaf structure of plants is specially adapted to this purpose. The equation of photosynthesis is CO2 + H2O ? C6H12O6 + O2 The Structure of a Leaf (left) 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. Light 6CO2 + 6H2O ? 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. ...read more.

Middle

The Blu-Tac / Plasticene / paperclip is used to weigh down the Elodea specimen in the boiling tube.. This makes sure that the entire plant is submerged in the Na+HCO3- solution and therefore the entire plant is exposed to the CO2 released by the Na+HCO3-. However, this weight covers as few leaves as possible, thus reducing the chance that the CO2 production / release will be interfered with. 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) ...read more.

Conclusion

Evaluation I feel that this experiment has been successful in fulfilling the objective. 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. ...read more.

This student written piece of work is one of many that can be found in our GCSE Green Plants as Organisms section.