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In my investigation I aim to determine whether intensity of light would affect the rate of photosynthesis in a plant.

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Gabriel Clark 1010 How does light intensity affect the rate of photosynthesis? In my investigation I aim to determine whether intensity of light would affect the rate of photosynthesis in a plant. Introduction Photosynthesis can only happen if light is present, and takes place in the chloroplasts of green plant cells. Photosynthesis is the production of simple sugars from carbon dioxide and water causing the release of sugar and oxygen. The chemical equation for photosynthesis can be expressed as: (light) 6CO2 + 6H2O --> ( C6H12O6 + 6O2) The reason that light intensity may affect the rate of photosynthesis is that as light (energy), falls on the chloroplasts in a leaf, it is trapped by the chlorophyll, which uses the energy for chemical reactions in the plant. Therefore the amount of light that falls on the plant will change the amount of energy absorbed, so affecting the energy available for the chemical reactions. However light is not the only factor that affects photosynthesis; light intensity, temperature, the amount of chlorophyll in the leaf/plant and carbon dioxide concentration. Predictions I predict that as the intensity of light increased, so will the rate of photosynthesis. Also I believe that the rate of photosynthesis will be directly proportional to the light intensity because it stands to reason that if light intensity increases consistently so will photosynthesis. ...read more.


Added to the water was a spatula full of sodium hydrocarbonate to speed up the reaction. The lamp was set up at the furthest distance from the plant (this was so it took longer for the water to change in temperature). The apparatus was left for exactly one minute for the reaction to begin and then the stopwatch was started and, for 1 minute the number of bubbles were counted. Observations Distance of light from plant (cm's) Number of bubbles per minute (exp 1) b.p.m. (exp 2) b.p.m. (exp 3 ) b.p.m (average) 25 8 14 11 11 20 16 10 10 12 15 20 13 12 15 10 24 22 23 23 5 27 28 26 27 0 28 31 34 31 Gabriel Clark 1010 Gabriel Clark 1010 Analysis From the results obtained I have been able to draw a graph of my findings. The graph shows a direct pattern between light intensity and photosynthesis: As the light intensity increased so did the rate of photosynthesis. I believe this is the case because photosynthesis is a reaction and needs energy from light to work, so as the amount of energy available from light increased with the rise in light intensity, so did the amount of oxygen produced as a product of photosynthesis e.g. the faster the reaction. ...read more.


This could explain why my graph was a curve as opposed to a straight line, that is something to be investigated further. A way round the temperature problem would be to place a Perspex block between the lamp and the plant, which would absorb most of the heat, while allowing the light energy to pass through. The final inaccuracy apparent, though a small one, was in the time keeping. The main problem here was in when exactly to begin the minute. If for one reading, the minute was started just after one bubble had been produced, and in another reading it was just before, the readings could be influenced and would have had a negative effect on the accuracy of my results. Next time I could ensure that in each case I started the stopwatch just after a bubble had been produced, so increasing the accuracy. Overall I believe however my investigation was reliable and successful, the correct results were obtained and no injuries or breakages occurred. I have also had ideas on how to extend my enquiries further. I could perhaps try to link in some of the other limiting factors to the same experiment such as temperature an maybe perhaps used heavy water instead of h2o. Whether I investigate further or not I can say I have successful found that the rate of photosynthesis increases with the light intensity. ...read more.

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