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Investigate a factor which may affect the rate of photosynthesis of Canadian pondweed.

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Biology Coursework - To investigate a factor which may affect the rate of photosynthesis of Canadian pondweed... Aim: I plan to investigate whether light intensity affects the rate of photosynthesis of a length of Canadian pondweed, or ELODEA. This plant is suitable because it naturally occurs in water, so placing it in water for a prolonged period of time would not disturb it. Light intensity is measured in arbitrary units, and is calculated by using the formula Intensity = distance(from lamp) -2 or Intensity = 1 ? distance (from lamp)2 As the distance from the lamp increases, so the intensity decreases - they are INVERSELY PROPORTIONAL. Photosynthesis is a chemical reaction in plants that converts carbon dioxide and water into glucose and oxygen via a substance called CHLOROPHYLL. This is a green-pigmented chemical that absorbs sunlight and uses the energy to split water, thereby giving off oxygen bubbles. ...read more.


I will place an inverted syringe, filled with water, on top of the funnel, and use this to measure the volume of gas collected. The apparatus will then be placed at different distances from the irradiator, and I will use each distance to calculate the intensity of the light reaching the set-up. I will leave the apparatus like this for enough time to collect a measurable amount of gas, but so I can fit in as many different experiments as possible - and every 2 minutes I will record the volume of gas collected. Diagram: Table of Results: Distance (cm) Intensity (1/d2) Bubble Count Amended Intensity (intensity x 100,000) 10 0.01 72 1000 20 0.0025 80 250 30 0.001111111 107 111.1111111 40 0.000625 55 62.5 50 0.0004 53 40 60 0.000277778 28 27.77777778 70 0.000204082 23 20.40816327 80 0.00015625 19 15.625 90 0.000123457 14 12.34567901 100 0.0001 7 10 Analysis: From my results I gather that my hypothesis was correct, although the results are not an accurate display of this fact. ...read more.


Instead I just counted the number of bubbles. This proved not so accurate, but a lot easier to do. My hypothesis was proved correct, as the curve shows that there is (sort of...) a positive correlation between light intensity and bubble count. Evaluation: The experiment was not a resounding success, but did merely what I set out to do - prove my hypothesis correct, if only slightly. In order that I could obtain more accurate results, I could have done many things, including: � found the correct equipment to measure the volume, and done so � used a light meter to gauge the light intensity � repeated each distance more times to obtain an accurate average � used an automated data-logging machine of some kind to count the bubbles, thereby eliminating the factor of human error � found the rate of the reaction by involving time in my calculations Overall, my experiment was not astoundingly impressive, but served my purpose very well. ...read more.

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