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How does light intensity affect the rate of photosynthesis?

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How does light intensity affect the rate of photosynthesis? Questions 1) How does light intensity affect the rate of photosynthesis? Prediction I predict that the more intense the light, the higher the rate of photosynthesis. To photosynthesise, plants need light. It provides the energy for the process to happen. Chlorophyll is an enzyme and it speeds up the reaction. If a plant does not get enough of either of these things, photosynthesis will not happen as quickly, if at all. Therefore, I predict that when the light is not very intense we will not see so many bubbles being produced. This is because the plant will not have so much energy (derived from light) to activate photosynthesis. All reactions require a certain activation energy, and if this is not reached the reaction will occur more slowly. I think that as we move the lamp away (and therefore reduce the light intensity) from the elodea pondweed the number of bubbles produced will decrease steadily. For instance, say at 10cm distance 50 bubbles are counted, it is likely that at 20cm distance 25 bubbles will be counted, as the lamp is twice the distance away. This means the rate of photosynthesis is halved. I think that if we move the lamp any further away than 50cm no bubbles at all will be produced because there will simply not be enough light for photosynthesis to work. Plan Apparatus desk lamp Elodea pondweed x 2 boiling tube x 2 paperclip x 2 250ml glass beaker x 2 test tube rack thermometer sodium hydrogen carbonate solution stopwatch ice tongs metre stick black A4 paper sellotape scissors 1ml pipette Method Preliminary work... ...read more.


This should give reliable results, because of repeated readings and the range of 10-50cm in intervals of 10cm. If the pondweed stops bubbling at any time during the experiment, this may be due to an air lock in the xylem tubes of the plant. In this case you need to cut the end of the pondweed with no leaves on while it is still under the water. This should stop the air from blocking up the xylem tubes of the plant. The other problem may be that the plant has used up all the carbon dioxide form the sodium hydrogen carbonate solution. In this case you need to add two or three 1ml pipettes of the solution to the water the pondweed is in. Variables the dependant variable is light intensity the indedendent variable is the rate of photosynthesis 1) the power of the light bulb 2) the piece of pondweed 3) adjustment time 4) temperature Conclusion I conclude that the greater the light intensity, the quicker the rate of reaction. For photosynthesis, plants require light and chlorophyll to make the reaction happen. They are not constituents of glucose but are still vital. So, when the lamp was further away from the pondweed the plant was unable to photosynthesis as well as when the lamp was right up close to the pondweed. When the lamp was 50cm away, an average of just 3 bubbles was produced, compared to an average of 25 for 10cm away. ...read more.


However, at least the results were not completely anomalous and I was able to draw reasonable conclusions from them. There is not really any way in which we could improve this procedure, because living things are so unreliable. However, we could take results over a period of several weeks for more accuracy. This way we would catch the pondweed at times when it was working at a high level and at times when it was working at a low level. Another thing that was not very suitable was the way of measuring the rate of reaction. Counting the bubbles got very boring and I could easily have miscounted, leading to anomalous results. A better way would be to find some way of collecting the oxygen bubbles in a capillary tube and measuring how far along the oxygen goes. We would have to fill the capillary tube with water and seal the top, and attach the tube to the pondweed. Although fiddly this would be more reliable. There were no anomalous results, but if there were there are many reasons why it could be. For a start, I could have miscounted the bubbles. Also, the pondweed might not have been bubbling properly due to an air lock that I did not notice. Similarly, there might not have been enough sodium hydrogen carbonate solution, which provides carbon dioxide for the plant. Also, there is the possibility that the piece of pondweed used was damaged - for example perhaps it had been heated up too much and the chlorophyll had become denatured. Because there were no anomalies, this supports my prediction in that they were reliable. ...read more.

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