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Which factors affect the rate of photosynthesis?

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Which factors affect the rate of photosynthesis? Introduction Plants, like all living organisms, need a supply of food. They need it as a source of energy in respiration and they need it as a source of raw materials to build new cells and tissues as they grow. Food is a kind of "fuel" which drives essential living processes and brings about chemical changes. Animals take in food, digest it, and use the digested products to build their tissues or to produce energy. Plants also need energy and raw materials, but apart from a few insect eating species (e.g. Venus flytrap) plants do not appear to take in food, the most likely source of their raw materials would appear to be the soil however it has been proved that water and air are additional sources. Photosynthesis Photosynthesis is the chemical process of separating oxygen from water which then combines with carbon dioxide to synthesize simple food stuffs such as glucose. It occurs in the chloroplasts of cells. Oxygen gas is released through the stomata Limiting factors A limiting factor is a factor that determines the rate of a reaction. In this case the limiting factors are the main factors which can affect the rate of photosynthesis: * Light intensity (and wave length) * Carbon dioxide concentration * Temperature Increasing each of these will increase photosynthesis, up to a certain maximum value. For example, low light intensity limits photosynthesis even if the carbon dioxide concentration is high. * Chlorophyll could also be considered a variable because if there is more chlorophyll then more light can be trapped which will speed up the process. This needs to be controlled by using the same piece of pondweed for the experiments. The site of photosynthesis For photosynthesis to occur, carbon dioxide, water and light energy must come together where there is chlorophyll in the flowering plant. Leaves, which are usually broad and flat, are the parts of the plant most suitable for photosynthesis; this is because: * Contain chlorophyll. ...read more.


* The lamp must not be kept too close to the leaves for a long period of time. This is because chlorophyll is an enzyme and gets denatured by excessive heat. * Bags and blazers must be kept under benches so that you are less likely to trip over things. * Wear safety goggles and aprons so that the sodium hydrogencarbonate cannot get into your eyes as it would cause irritation. * Never run in the laboratory because it could cause an accident. * Tie long hair back so that it cannot get in the way and become dangerous. * Wash hands after practical so that anything you have picked up from the pondweed is washed off. * The lamp will become hot if it is left on for long periods of time so care must be taken at the end of the practical when it has to be moved. Why I did a pilot I did a pilot experiment so that I could make sure my method worked and also that I was getting sensible results. It gave me an idea of what to expect for my actual investigation. I also did a preliminary test to make sure I was comfortable with the experiment. My results, although they were not thorough, show a relationship, as I have already stated, forming. The rate of photosynthesis was going up at a fairly similar rate to the light intensity so I am confident that in the actual experiment the results will be closer to the graph above and show a directly proportional line on the graph. The results for my preliminary experiment: Distance from beaker (m) Number of oxygen bubbles produced in 5 minutes Light intensity Rate of photosynthesis 1 2 3 Average 0.05 137 145 140 140.6 400 0.469 0.1 115 121 119 118.3 100 0.394 0.5 22 17 19 19.3 4 0.064 What I discovered from my preliminary measurements In my preliminary experiment I learnt what to expect for the real experiment so this prepared me in many ways. ...read more.


The amount of oxygen dissolved or used by microbes is probably insignificant to my results since the degree of accuracy at which I measured was not high enough. Some oxygen is also used during the respiration of the plant. But since only bubbles were counted, the volume of bubbles was not as important. But the volume of oxygen produced is important, since it was volume in terms of bubbles that were measured. As the rate of photosynthesis decreased due to a decrease in light intensity, the size of the bubbles produced also became smaller. This change in bubble size was not accounted for when the results were analyzed. For a more accurate analysis of the collected data, volume should have been measured instead of bubble quantity since the size of bubbles can vary. Using a measuring cylinder in place of the test tube so that the volume of each bubble could have been measured could have done this. During the high light intensities I had experienced counting difficulties of the bubbles being produced. There are also factors affecting accuracy at low light intensities. With low light intensity, the pondweed receives some light energy from background light such as sunlight seeping through curtains or the light from the lamp of another student's experiment. To eliminate almost all background light, the experiment must be performed in a completely dark room. Even then, some of the light from the lamp in my experiment would reflect of the beaker and reach the plant though this amount of light is probably insignificant in affecting the rate of photosynthesis. If during a repeated experiment, counting bubbles is still used, there is a smaller chance for human error when counting within a smaller time frame. If the measuring cylinder option was to be chosen, volume should be measured for a smaller time frame to reduce the overall time to complete the experiment. Also, during high rates of photosynthesis, it would still be difficult and impractical to measure the volume of oxygen produced for a long duration. March 2003 Lucy Blackbourn 1 ...read more.

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