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Effects of temperature and carbon dioxide on photosynthetic rate in Elodea.

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A2 Biology- Effects of temperature and carbon dioxide on photosynthetic rate in Elodea. Aim: to investigate the effects of temperature and carbon dioxide on the photosynthetic rate of Elodea. Background knowledge: Photosynthesis is the use of light energy from the sun to fix carbon dioxide i.e. converted to sugars. These sugars can then be converted into other essential substances- fats and proteins etc.- that plants need to live and grow. Photosynthesis can be represented using the following equation: 6CO2 + 6H2O ? C6H12O6 + 6O2 The light independent stage occurs in the stroma. Firstly CO2 combines with a 5C compound called ribulose bisphosphate. This reaction is catalysed by the enzyme RuBPC. The 6C compound formed immediately splits into two molecules of glycerate-3-phosphate (GP). The GP molecules are converted into molecules of triose phosphate (TP) using energy from ATP and the hydrogen atom from NADPH. Some of the TP is used to regenerate RuBP. Finally the rest of the TP is used to produce other essential substances that the plant needs- fats, proteins etc. As light intensity is increased, photosynthesis begins, and some carbon dioxide from respiration is utilised in photosynthesis and so less is evolved. With a continuing increase in light intensity a point is reached where carbon dioxide is neither evolved nor absorbed. At this point the carbon dioxide produced in respiration exactly balances that being used in photosynthesis. 'This is called the compensation point'1. 'Further increases in light intensity result in a proportional increase in the rate of photosynthesis until light saturation is reached'2. Beyond this point further increases in light intensity have no effect on the rate of photosynthesis. If, however, more carbon dioxide is made available to the plant, further increases in light intensity do increase the rate of photosynthesis until light saturation is again reached, only this time at a higher light intensity. ...read more.


Remember the concentration of NaHCO3 must remain constant throughout this experiment. Risk assessment: * Wear safety goggles and take care when handling chemicals, such as NaHCO3 solution, to prevent any foreign particles from entering the eye. * Tie long hair back if using Bunsen burner to prevent obstruction of sight, and to prevent accidents. * Care should be taken when handling the sodium hydrogen carbonate solution as it maybe irritating to eyes and skin. * Take care when handling the Bunsen burner as you may burn yourself. * Do not sit down during the experiment, especially when Bunsen burners are alight, and keep all chairs/stools out of the way as these will slow down reaction time, in case of an emergency. * Care should be taken when handling the scalpel, as it is a sharp object and can cause injury if mishandled. * Take care when handling the beakers after heating the contents, as they may be hot. * To avoid accidents, wipe any spillage immediately and maintain organization throughout the experiment. * While the Bunsen burner is not in use ensure that the safety/yellow flame can be seen. Results: Tables showing the volume of O2 produced at different concentrations of NaHCO3 and different temperatures. Temperature 10?c. Concentration of NaHCO3 solution, in mol dm3. Volume of O2 produced, in cm3. 0 0.12 0.10 0.10 0.10 0.10 0.00 0.01 0.40 0.46 0.38 0.36 0.38 0.44 0.025 0.63 0.63 0.65 0.62 0.62 0.63 0.60 0.55 0.55 0.05 0.62 0.62 0.50 Temperature 20?c. Concentration of NaHCO3 solution, in mol dm3. Volume of O2 produced, in cm3. 0 0.25 0.36 0.20 0.20 0.22 0.20 0.01 0.80 0.86 0.75 0.72 0.75 0.88 0.025 1.30 1.30 1.25 1.25 1.25 1.25 1.20 1.18 1.10 0.05 1.20 1.20 1.00 Temperature 30?c. ...read more.


Modifications: Limitations. * The room temperature may fluctuate. * The concentration of carbon dioxide in the water may be reduced during experiment. * The rate of gas evolution is not consistent. * There are other light sources, which may interfere with the results. * Artificial light will increase temperature, as a 60watt bulb will be used, some energy will be lost as heat energy. * Are the bubbles being observed actually oxygen? Setting up the apparatus and placing it in a water bath may overcome the first error. Doing so will ensure that a constant temperature is maintained throughout the experiment. To avoid other light sources interfering with the experiment shelter the apparatus up so that the pondweed only receives light from the table lamp. To ensure consistency of gas evolution when changing to a new condition, the plant should be equilibrated for at least 10 minutes before taking any readings. Using a dilute sodium hydrogen carbonate solution ensures a constant supply of carbon dioxide to the pondweed, avoiding fluctuation of carbon dioxide concentrations. To test for presence of oxygen simply lower a glowing splint into the test tube containing the gas; if the splint relights this indicates that oxygen is present. Using this test increases reliability of the results. The presence of the lamp may cause the temperature to increase; to prevent this from happening ice can be used to maintain a constant temperature. Further experiments could be implemented to test other factors that may have an affect on the rate of photosynthesis. Light intensity has been found to have an affect on photosynthesis. This can be investigated by placing a light at varying distances from the elodea plant and recording the number of bubbles produced. Other experiments in this area could also include testing the rate of photosynthesis with different amounts of chlorophyll in the plants. ...read more.

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