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Photosynthesis and Limiting Factors

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AT1: Photosynthesis and Limiting Factors Aim: In this experiment, I will test to see how heat affects the rate of photosynthesis in a water plant as a limiting factor. Background Knowledge: Photosynthesis is the process by which chlorophyll containing organisms, (namely green plants, algae, and some bacteria), capture energy in the form of light and convert it to chemical energy. Virtually all the energy available for life in the earth's biosphere, (the zone in which life can exist), is made available through photosynthesis. A generalized chemical equation for photosynthesis is: Carbon Dioxide + Water + light energy = Sugar (Glucose) + Oxygen + Water This can be seen as two different chains of reactions... One involves the transfer of light energy into chemical energy that is light intensity dependant - if it is lighter the reaction happens more efficiently. The other shows the creation of glucose and is heat dependant. The glucose is created by carbon dioxide and water, and the reaction is powered by the chemical energy converted from solar energy. The carbon dioxide must be broken down using enzymes to form the basics of the glucose. This is heat dependant because enzymes work better at higher temperatures. This creates glucose (C6H12O6) and waste products, oxygen (O2) and a little water (H2O). Artificial Photosynthesis If chemists were able to duplicate photosynthesis by artificial means it would result in systems having enormous potential for tapping solar energy on a large scale. ...read more.


I will also keep the amount of carbon dioxide in the water constant by changing the water after each test. If there is too little carbon dioxide in the water then the rate is decreased because the plant has no carbon dioxide to use in the photosynthesis reaction. I will keep the plant the same length of 5cm and the same species of pondweed (Elodea). Outcome: - I will measure the temperature of the water with a thermometer to get an accurate fair temperature for the plant to be in. I will also count the number of bubbles that the plant gives off. To keep it fair I will obey the variables and do the test at each temperature 3 times to clear any anomalous results. This will be so that if are any anomalous results then I can reject them without creating a gap in my results. To keep this experiment safe I will mop up any water that I drop near the lamp or plug to stop any chance of electrocution. I will also keep in mind the heat that the lamp generates so I will be careful to not touch it. Results Temperature Number of bubbles 1st test 2nd test 3rd test Average 0 C 2 3 3 2.7 10 C 3 5 5 4.3 20 C 5 7 9 7 30 C 12 11 11.5 40 C 16 17 20 17.7 50 C 6 4 5 ...read more.


Therefore, I think that I can improve this experiment a lot. Firstly, I think that the control of the environment should be improved; the best way of doing this would be to go to a dark room, sealed off from light. I would be on my own and the room would need good ventilation. Secondly, I think that the experiment itself had serious flaws. Counting bubbles is a rudimentary method of measuring. It would be better to use displacement of water as a measurement. This way I could measure in ml instead of bubbles that could be different sizes. It would look like this: The larger beaker is so that there is always water to give up its oxygen to the plant. With this more advanced apparatus, all I need to do is find the difference between the amount of water in the beaker at the start and at the end. I would also do the experiment for longer, for 30 minutes because otherwise there would not be enough collected oxygen to show for anything. This new experiment does not have the rudimentary form of miscounting any bubbles. Also, I would have a larger, 10cm piece of weed. This would provide a more stable and reliable set of results as the measurement method is more accurate and can be measured by volume. With this information, I could draw up a more detailed, reliable and accurate conclusion because I would have superior results and I could use this experiment as a precursory experiment. ...read more.

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A reasonable account of the investigation but let down by a lack of attention to detail.

Marked by teacher Adam Roberts 20/05/2013

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