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The effects of light intensity on the rate of photosynthesis.

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Biology Investigation The effects of light intensity on the rate of photosynthesis Introduction Photosynthesis involves an energy conversion in which light energy usually in the form of sunlight is converted into chemical energy stored in molecules of carbohydrate. The equation for photosynthesis is: The chlorophyll in the leaves of the plants absorbs the light energy. Some of this energy is used to produce ATP and some is used to split water molecules in the photolysis of water1. Light intensity as a limiting factor The amount of light available affects the amount of chlorophyll, which has excited electrons and therefore the amount of NADPH and ADP produced in the light-dependant stage. If there is a low level of light then insufficient NADPH and ATP will be produced to allow the reactions of the light independent stage to progress at their maximum rate. In this situation light is said to be the limiting factor for the process2. Also, not all wavelengths of light are equally effective at powering photosynthesis. However in my experiment I will be using a bulb, which will produce white light, as I know this, is an effective wavelength because the light from the sun is also white light3. Controlling the other limiting factors in photosynthesis If there is an insufficient supply of carbon dioxide in the reaction then there will not be enough available for fixation on the Calvin cycle, which means that the reaction cannot proceed at the maximum rate. ...read more.


Materials * Photosynthometers * Elodea- freshly cut at each end * Thermometer * Water * Clamp stand * Metre rule * Light bulb (100W) * Syringe * Sodium Hydrocarbonate Diagram of apparatus Method * Assemble the apparatus as shown in the diagram * Push in the plunger to the end of the syringe, making sure that there are no air bubbles in the tubing * Add 0.25g of Sodium Hydrocarbonate to the test tube with the elodea and stir it to dissolve * Measure the distance between the light bulb and the Elodea * Switch on the light bulb * Leave the Elodea to equilibrate * Then collect the oxygen given off for 5 minutes * Using the plunger in the syringe, carefully draw the bubbles up into the tube so that you can measure the length of the bubble. * Record this length * Repeat this procedure, each time moving the lamp away from the Elodea and measuring the distance * Throughout the experiment regularly checking the thermometer to make sure the temperature of the water remains constant. Results Length of bubble produced in mms Distance between light bulb and Elodea in cms Test 1 Test 2 Test 3 Average 0 70 34 76 60 10 12 15 32 19.66 20 6 10 23 13 30 3 6 12 7 40 2 3 5 3.33 50 1 1 2 1.33 After repeating my experiment 3 times I ...read more.


In my preliminary work I did a couple of tests using different amounts of sodium hydrocarbonate each time so that I knew that there would be an excess of carbon dioxide so that it would not be a limiting factor. I left the elodea to equilibrate before I began each test to let the plant adjust to the surroundings and allow it to perform photosynthesis at a constant rate I was also extremely vigilant with the amount of time I left the elodea to equilibrate, as I knew that this would have a rather dramatic effect on my results. I put a thermometer into the water surrounding the test tube so that I was able to keep a constant temperature. It was difficult to use exactly the same amount of Elodea each time so if I did this experiment again I would consider weighing the Elodea so that my results were more accurate. If I were to perform this experiment again then I would use a larger piece of elodea. This would mean that the amount of oxygen would have been larger and I could possibly decrease the light intensity to a greater extent and still be able to accurately measure the length of the bubble produced. Overall I think that my experiment worked out fairly well, as my results were similar to those, which I had expected. In my experiment I was able to prove that the rate of photosynthesis is affected by the light intensity. ...read more.

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