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Experiment - Influencing the Rate of Photosynthesis with Light Intensity and Carbon Dioxide Concentration

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Aylin Humzeli April, 07 2011 Influencing the Rate of Photosynthesis with Light Intensity and Carbon Dioxide Concentration Introduction Background: Photosynthesis is the process plants use to produce organic molecules, usually carbohydrates, from carbon dioxide and water by using sunlight or an alternative source of light. The light is used as energy which is absorbed by chlorophyll in the chloroplast of plants. Photosynthesis is comprised of two different reactions: the light-dependent reaction and the light-independent reaction. The light independent reaction is powered by light energy and produces ATP and NADPH, as well as oxygen as its waste product. The light independent reaction is powered by the NADPH produced in the light dependent reaction and produces sugars using carbon dioxide. The general formula for photosynthesis is: 6H2O + 6CO2 + Energy ==> 6O2 + 2 C3H6O3 The rate of photosynthesis can be affected by 3 factors: light intensity, carbon dioxide concentration, and temperature. An increase in light intensity increases the energy absorbed by the chlorophyll, and hence increases the rate of photosynthesis to a point. Increase in the amount of carbon dioxide increases the amount of carbon dioxide available to the enzymes to catalyze. Carbon dioxide concentration increases the rate of photosynthesis only to a point, specifically, when the enzymes are saturated. Since photosynthesis depends on enzymes, an increase in temperature increases the rate of photosynthesis to a point, for the enzymes have reached their optimum temperature. ...read more.


Uncertainties: The distance between the lamp and the test tube was measured with a normal metric ruler. The ruler's smallest measurement was 0.1, half of this is 0.05 which is the ruler's uncertainty. The uncertainty for time was 0.01 seconds which is the smallest unit measurable with a digital stop watch. The uncertainty for the amount of sodium bicarbonate is 0.01 grams which is the smallest value measurable with a digital scale. Results: The data and graph show that when the distance of the lamp is 5 cm and sodium bicarbonate is added the average number of bubbles produced is the highest. The average number of bubbles produced is followed by the lamp at 5 cm without sodium bicarbonate. The condition with the lamp 20 cm away produced the smallest number of bubbles. The second trial of the lamp at 5 cm away produced more bubbles. The second trial for the condition of 20 cm distance produced less bubbles than the first trial. The second trial with the lamp at 5 cm and with sodium bicarbonate produced a lower number of bubbles than the first trial. Conclusion: As the graph shows, the most bubbles were produced when the light intensity was closest, at 5 cms, and when sodium bicarbonate was added. The least amount of bubbles was produced when the light source was 20 cm away and with no sodium bicarbonate added. ...read more.


For more accurate average, more trials should be done. This would decrease the amount of deviation of the number of bubbles produced and would produce a better average value. Unfortunately, the error which comes from using the same elodea cannot be reduced. For using a different plant for each experiment would also affect the data for the plant would vary in surface area and freshness. However, the data still did allow one to see the effect of each condition correctly. Instead of counting the number of oxygen bubbles produced, the test tube would the elodea could be covered so that no gas escapes. The test tube could then be connected to a beaker which is on scale or another instrument to measure mass. Then as the plant produces oxygen, the mass produced could be measured rather than having to count the bubbles which can be affected by human error. Since the objective of the lab is to observe how factors influence the rate of photosynthesis. The experiment could be extended so that it also observes how temperature affects the rate of photosynthesis by submerging the plant in different temperature water. Also, instead of just using white light, different colored lights or transparent glossy paper to see the affect of different colored light on plants. Also, a wider number of distances would improve the experiment for it would provide better accuracy of how light intensity affects the rate of reaction. ?? ?? ?? ?? 1 ...read more.

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