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Photosynthesis Investigation

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Photosynthesis Investigation Prediction The equation for photosynthesis is: Water + Carbon Dioxide Glucose + Oxygen 6H2O (l) 6CO2 (g) C6H12O6 (aq) 6O2 From this equation it is seen that sunlight is very important in the production of glucose. If all other products are available e.g. water and carbon dioxide in sufficient quantities then light can be used as a variable. If not enough of any reactant is present it will be a limiting factor. This means that no matter how much light is added no more glucose can be made. In our experiment the plant i.e. elodea is placed in water and sodium hydrogen carbonate is added thereby preventing a limiting factor. This is because the water of course is plentiful and the sodium hydrogen carbonate provides the elodea with carbon dioxide. The only way that a limiting factor can be reached is if the temperature rises too high. To prevent this we placed a beaker in front of the light source, which absorbed the heat. The beaker also prevented an increase in temperature as the lamp was moved closer to the elodea. The introduction of the beaker stopped an additional factor entering the experiment. As a limiting factor is unlikely to occur I anticipate that there will be a positive correlation between the rate of photosynthesis and the light intensity. This means that as the light intensity doubles the rate of photosynthesis doubles also. Plants are always respiring but during the light stage the carbon dioxide that should be released is used as for the production of starch by photosynthesis. During the dark stage though the carbon dioxide is released, as photosynthesis is not taking place, due to a lack of sunlight. When the plant respires it takes in oxygen and gets rid of carbon dioxide just like a human. While making food however the processed is reversed with carbon dioxide being absorbed and oxygen being given off. ...read more.


Also there is an inverse proportion between the rate of photosynthesis and the distance of the elodea from the light source. This shows that the closer a plant is to light the higher the light intensity and the higher the rate of photosynthesis. Plant's distance from light (cm) 10 20 30 40 50 0.5 0.7 0.3 0.1 less than 0.1 0.8 1 0.5 0.2 0.1 Amount 1.5 1.8 0.7 0.4 0.1 Of 2 2.1 1 0.6 0.2 Oxygen 2.6 2.6 1.2 0.7 0.3 Produced 3.1 3 1.6 0.8 0.4 (Cm) 3.5 3.3 1.9 0.9 0.4 4 3.5 2.1 1 0.5 4.6 3.8 2.4 1.1 0.5 Total amount of oxygen produced (cm) 5.3 4.1 2.7 1.3 0.6 Average rate of photosynthesis (cm/min) 0.53 0.41 0.27 0.13 0.06 Volume of oxygen produced (cm3) 0.6 0.52 0.34 0.16 0.075 Volume = ?x r2 x h R = radius of capillary tube = 0.2 H = Total amount of oxygen produced The results above are those that I found from my experiment. Due to events beyond my control the results from my experiment appear lower and are less accurate. To compensate I have found results from an identical experiment carried out by some other students at a school. Their results are more useful to analyse as they took many results and must not have had problems equalling mine during their experiment. Their results: Light Intensity arb. units Distance of lamp to weed Set 1 Set 2 Set 3 Set 4 Set 5 Set 6 Set 7 Set 8 Set 9 16 10 25 26 26 28 25 27 26 19 26 8 14 24 24 25 13 22 15 24 8 22 4 20 19 18 18 12 18 7 20 7 11 2 28 16 13 15 11 7 5 14 5 9 1 40 10 9 13 6 2 3 11 3 5 These results reflect the same trend as my results but they are more accurate as they are more results. ...read more.


My expected graph is fairly similar to the outcome but as I have already said it does not reflect the forty-five degree gradient causing a definite direct proportional graph. In my prediction I thought that the line of best fit would show that as one value is double the other doubles also but really this is not the case. If I were to redo the experiment there would be some major and minor changes that I would make. Firstly I would hope that the electricity would not keep cutting out so I could carry out the experiment easier and more accurately. Also I would make sure I checked the thermometer more as in the last experiment it was not checked as often as it should have. Maybe instead of using a thermometer a temperature probe could be used to guarantee the temperature did not get too high or low. This way it would be easier and would make sure that the temperature was checked and not be down to me while I handle everything else. I would try and find a better way of preventing the heat from reaching the elodea, as the beaker was effective. I may use a heatproof screen which would let only light through. This way it would be easier to set up and more safe at more elevated heights. Also while marking the air bubble on the capillary tube the mark was thick which could have slightly affected the results. I could use a pen with a thinner nib or mark it using string or wire. Also I could have tried to control the background light more efficiently by covering the whole experiment perhaps. If a black bag was tied around the light and elodea it would make sure that the experiment was a total fair test with no extra light. Also to test if this proportion worked for all plants I could try and set up an experiment using another plant. Mrs Knight Andrew Fowler 28 April 2007 ...read more.

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