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Investigation Into the Factors Affecting the Rate of Photosynthesis

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Introduction

INVESTIGATION INTO THE FACTORS AFFECTING THE RATE OF PHOTOSYNTHESIS AIM- To identify the factors affecting the rate of photosynthesis and, choosing one factor, to ascertain the effects it has. Photosynthesis is an endothermic reaction that occurs in plants, by which plants use light energy to make glucose. It needs energy from the photons of light and it is their anabolic effect on the plant that gives the energy for the reaction to take place. During this process carbon dioxide combines with water to from glucose, and oxygen is released. The glucose made then has many uses in the plant: respiration, making ATP, active uptake.... Sunlight and chlorophyll must be present for the reaction to take place, and the light is trapped in the chlorophyll: sunlight Carbon dioxide + Water Glucose + Oxygen. Chlorophyll The amount of oxygen given off is an indication of the rate of photosynthesis. The more oxygen being given off, clearly the faster the rate of the reaction, and the more photosynthesis occurring / the faster the rate of photosynthesis. POSSIBLE VARIABLES- from background research and previous experiments I know the following variables/ limiting factors to affect the rate of photosynthesis: * Light Intensity - the basic energy source * Temperature- increases enzyme reactions until the point of denature. * Water- a basic reagent- a lack of water also causes stomata to close inhibiting diffusion of CO2 in and out of the leaf. * Chlorophyll- this is what traps the light energy for the reaction * Carbon dioxide - the more CO2 in the air, the more that can diffuse into the leaf to be a basic reagent for the photosynthesis reaction. Of these variables I have chosen to investigate light intensity because there are various reasons why other variables would not be suitable: * Temperature- this variable is not specific to increasing the rate of photosynthesis, but rather to general rates of reaction, as I have seen in previous experiments into reaction rates. ...read more.

Middle

Therefore our results must be at much smaller intervals as fore-mentioned. * I shall try to repeat each experiment twice so that any inaccurate results will be noticed, and so that I get more accurate results (by taking averages from a larger amount of data). For most experiments a control is needed, to which we can compare our results. In this case, we will leave one weed in the dark, and attempt to exclude all light, so we can observe what would happen in terms of photosynthesis and oxygen produced if the plant received no light at all. Obviously we will not be able to count bubbles as they are released in the dark, but we will be able to observe whether after the 10 minutes any oxygen was given off at all. I would predict that it would not be as plants do not photosynthesise in the dark. Any gas that is given off is likely to be carbon dioxide, as plants also respire all the time. We could then use this information to find out how much of the bubbles from our other results were in fact oxygen, or carbon dioxide from respiration. We will then vary the amount of light the plant receives, at set intervals (as mentioned above), and compare this data to the control. PLAN OF RESULTS TABLE Distance between lamp and Elodea (cm) Number of oxygen bubbles produced Temperature of the water (oC) result 1 result 2 average no lamp- in dark 2 4 6 8 10 METHOD 1. Cut 22cm of elodea on the white tile using a razor blade and taking care not to cut yourself. 2. Set up apparatus as shown below: 3. Place one spatula of sodium hydrogen carbonate into the water so that CO2 is in abundance and is not the limiting factor. 4. Place in the dark and leave for 10 minutes (record time using the stop watch) ...read more.

Conclusion

* Some of the gas given off may have been carbon dioxide from the plant's respiration, but again, this was unlikely to mar my results, as they would all have been affected at the same rate. Also most of this gas would have been used up in photosynthesis, so the volumes would have been minimal. * As previously mentioned, when observing the bubbles I noticed that they were all of different sizes. It was hard to judge which I should consider for observation, as some were of negligible size. I decided therefore to count all the bubbles I could, both large and small, even though this may also have resulted in some error. To combat this in the future I could collect the oxygen produced in a gas syringe, or inverted measuring cylinder, to measure the volume, which would be much more accurate than counting bubbles. Having said all of this, I believe that the evidence collected, supported by my evidence from research and previous enquiries, was sufficient on which to base firm conclusions. However, for further confirmation, and also more insight into the topic as a whole, I could extend the enquiry by doing the following things: * I could vary one other or all of the other variables mentioned in my plan. * A sensible extra variable to investigate would be the colour, and therefore the wavelength, of the light, keeping the intensity of the light constant this time. Taking into account that plants are green, and so this light will not be as effective for photosynthesis.... I could also vary the wavelength of light, trying to coincide this factor with the one I already investigated (the greater the intensity of light, the greater the rate of photosynthesis). * I could repeat my experiments to get a wider range of data, leaving each one for a longer period. * I could investigate different sorts of plants and see whether there is any difference in photosynthesis rate depending on their habitat/environment. ...read more.

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