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To investigate the factors that affect the rate of photosynthesis.

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Key Stage 4 Biology Coursework Aim: to investigate the factors that affect the rate of photosynthesis. Planning Photosynthesis equation: carbon dioxide + water sunlight glucose + oxygen 6CO2 6H2O chlorophyll C6H12O6 6O2 Photosynthesis is the process that produces 'food' in plants. The food it produces is glucose. Photosynthesis takes place in the leaves of green plants. Plants need light, carbon dioxide, water and chlorophyll in order to photosynthesise. The leaf is where the food is made. It gets light usually from the sun. The carbon dioxide enters the leaf form the air around. Water comes form the soil, up to the stem and into the leaf. The most important thing is the chlorophyll, which is found in the chloroplasts. The chlorophyll absorbs the energy from the sunlight and uses it to combine carbon dioxide and water to produce glucose. Oxygen is a waste product. Therefore these are all limiting factors. The rate of photosynthesis is affected by a number of factors including light levels, temperature, availability of water, and availability of nutrients. If the conditions that the plant needs are improved the rate of photosynthesis should increase. The maximum rate of photosynthesis will be constrained by a limiting factor. This factor will prevent the rate of photosynthesis from rising above a certain level even if other conditions needed for photosynthesis are improved. This limiting factor will control the maximum possible rate of the photosynthetic reaction. The rate of photosynthesis can be measured by measuring the amount of oxygen given off. To do this you place the water plant in water under a funnel in a beaker full of water. Then place a test tube over the funnel and start counting the bubbles given off. The bubbles are oxygen bubbles. I know this from preliminary work because I tested the gas by putting a glowing splint into the test tube and it re-lit so this proves the gas is oxygen. The more oxygen bubbles there are, the faster the rate of reaction of photosynthesis. ...read more.


For example when the light intensity was 40 at 5cm the amount of oxygen bubbles collected was 40 whereas when the light intensity was 1.6 at 25cm there were only 1.5 oxygen bubbles given off. When I repeated the results a second time, they were fairly similar to the first trial, which proves my prediction was correct twice. As predicted when the light intensity increases so does the rate of photosynthesis. I predicted that a level would be reached where increasing the light intensity would have no more effect on the rate of reaction as there would be some other limiting factor, which limits the rate of the reaction. The rate increases at a steady rate as the light intensity increases until near the end of each line where the rate of increase decreases. This is either because the photosynthesis reaction has reached its maximum rate of reaction or another factor is limiting the rate. The fact that the curve levels off so quickly indicates that there is another limiting factor limiting the photosynthesis. It could be temperature. These tests are being carried out at room temperature so the temperature would have to be raised another 15�C before the enzymes in the plant's cells were at their optimum working temperature. More tests could be done by using water that was at a higher temperature to see what effect this would have on the photosynthesis rate. It is however impossible to raise the plant's temperature without affect other factors. For instance the actual amount of oxygen released by the plant is slightly more than the readings would suggest as some of the oxygen would dissolve into the water. At a higher temperature less oxygen would be able to dissolve into the water so the readings for the photosynthesis rate could be artificially increased. It is also possible that the photosynthetic reactions in the plant are occurring at their maximum possible rate and so can not be increased any more. ...read more.


It could also be interesting to explore the effects of coloured lights on the rate of photosynthesis, which could lead to the question of whether or not other types of light, such as fluorescent lights or halogen lights, would have a different effect on the rate of photosynthesis I think my results are fairly accurate because the results plotted on my graph show that they fit into a pattern. Also when I repeated the results a second time, they were fairly similar to the first trial, which proves my prediction was correct twice. If you repeated it more times you would get similar results, thus proving a successful method and reliable results. However, I realised that on my second trial, amount of bubbles was greater than the first trial so I think I should have let the water equilibrate for longer. I think my results are fairly accurate because most points fit on the line of best fit, and the other points are quite close to the line of best fit. The number of oxygen bubbles didn't completely stop increasing but if I had taken more readings they would have. To improve my experiment I could try other methods. For example, instead of counting the oxygen bubbles, I could measure the volume of oxygen collected. In this method the size of the bubbles would not affect the results so it would make the results more reliable. To extend my investigation, I could investigate if different coloured lights affect the rate of photosynthesis. For this investigation I used white light, so as an extension I could split up this light into the colours of the spectrum by using a coloured filter and find out if one colour has a different effect to the rate of photosynthesis than another. I know that plants reflect green light so I could also investigate if plants absorb one colour more than another does. Amreen Khadri 11QWR Amreen Khadri 11QWR ...read more.

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