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Investigating how the amount of oxygen given off by Pond weed changes when the environment is changed.

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Chris Wirt 1st December 2000 Investigating how the amount of oxygen given off by Pond weed, when the environment is changed. Aim: My aim is to do a well planned safe experiment. It should show clearly how the amount of oxygen given off by pond weed can be changed by changing the environment. Photosynthesis Equation: 6CO2 + 6H2O light energy & chlorophyll C6H12O6 + 6O2 Carbon dioxide + water carbon hydroxide + oxygen List of Equipment: When choosing the equipment for my investigation I have to take into account which will be the most appropriate for the task. * beaker 200ml * Thermometer * Stop watch * Funnel * 5cm piece of pond weed (Elodea) * water * lamp * 25w, 40w, 60w, 75w, 100w bulbs * test tube Variable: These are some possible variables I could use: * I could change the intensity of the light shone on the pond weed. I would do this by testing the amount of oxygen given off after a period of time, using different wattage bulbs. * I could change the colour of the light shone on the pond weed. I could easily do this by covering the head of the lamp with coloured translucent material. For the variable in my experiment I will be changing the Intensity of the Light shone apon the pond weed. The different wattage which I will use are 100w, 80w, 60w, 40w, 20w. Once I have allowed for the light to start effecting the weed I will be able to see how much oxygen is produced in a set time. ...read more.


As a watt is a unit of power, or work done per unit time, equal to 1 joule per second. It is used as a measure of electrical and mechanical power. One watt is the amount of power that is delivered to a component of an electric circuit when a current of 1 ampere flows through the component and a voltage of 1 volt exists across it. So basically the greater the wattage the more power that is applied to the device. So as I increase the wattage of the bulbs there is more power being used, and as more power is used more power is transferred to photosynthesis in the plant. So the rate of photosynthesis will increase as the watts do. This will only continue until the rate is stopped by other limiting factors, such as when all the carbon dioxide in the water is used up the reaction will stop. This can be clearly shown using graph 2 above as an example. Results: Bulb wattage (W) 1st try bubbles per min 2nd try bubbles per min 3rd try bubbles per min average bubbles per min temperature (�C) 25w 3.0 3.0 4.0 3.3 29.0 40w 4.0 6.0 6.0 5.3 29.0 60w 10.0 8.0 9.0 9.0 29.5 75w 17.0 19.0 17.0 17.7 29.5 100w 26.0 30.0 32.0 29.3 30.0 Conclusion: From the results I have gathered I can clearly say that the light intensity does increase the rate of photosynthesis in the plant. This will have happened due to when I increased the intensity of the light the result would be more energy being caught in the chlorophyll. ...read more.


The temperature was also another factor which could affect the rate of photosynthesis. This was a problem as most of the energy from a lamp is heat energy, so this could increase reaction speed. To make sure this was not happening we measured the temperature, which stayed between 29.0�C and 30?C. The method for my experiment could also be improved to generally increase the quality of my results. As I said before a gas syringe could be used to collect all the gas for greater accuracy. I also said that I was finding counting the number of bubbles a problem, this could be solved by only testing the rate of photosynthesis over a shorter period, such as 10seconds. Measuring over a shorter period of time will reduce the chance of human error as there are fewer bubbles to count and they are over a shorter period of time. Because of the way my experiment is set up it is easy for me to adapt to measure another variable of photosynthesis. As it is possible to control the amount of carbon dioxide in the water by using sodium hydrogen carbonate (NaHCO3). This could be easily done by using different volumes of NaHCO3. All other variables will be kept at constants. Another possible adaptation would be to alter the wavelength of the light used for photosynthesis. This would be done my using translucent colour filters in front of the lamps. The only problem is that there is no way to define or measure the wavelength of light. It is because of this point that we only have a basic way to class colours, that the coloured light experiment would not be as affective or interesting as light intensity or CO2 concentration. ...read more.

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