# The Effect of Altering the Light Intensity on the Rate of Photosynthesis of the Aquatic Plant Elodea

So that accurate conclusions can be come to we must first put ourresults into a table of values.Distance of lamp from plant (cm)Light intensity (lux)Length of bubble after 5 mins (mm)540007772682367591010003302722262115444.4151016149930111.143321045040122112We must now find an average bubble length for each distance, which wecan use to draw a graph. However care must be taken when working outthe averages. We must exclude any readings that are anomalous from theothers to ensure the results are as reliable as possible.Distance of lamp from plant (cm)Light intensity (lux)Length of bubble after 5 mins (mm)Average bubble length (mm)5400077726823675968.61010003302722262125.215444.4151016149912.230111.143321043.250401221121.5Now, so that we are able to make conclusions we must put the resultsinto graphs
To find any more relationships we must then compare the length of bubble to the light intensity. [image] Conclusion After putting the results into graph and table formats we are now able to explain them, coming to sensible conclusions for this experiment. Firstly we must describe and explain the graphs. The first graph drawn shows the relationship between the length of bubble produced and the distance the plant was from the light. From the graph you can see that the further away the light becomes the shorter the bubble becomes (the less the plant photosynthesises). The graph forms a curve that is very steep from 10-20cm that there but levels off at around 20-50cm. This means that at around 30cm the light begins not to effect the experiment and the results become much more similar. The second graph to be drawn shows the relationship between the length of the bubble and the light intensity. From the graph you can see that the more intense the light gets the longer the bubbles get (the more the plant photosynthesises). Again the graph is a curve, which begins quite steep from 0-1000lux, meaning that there is an increase of photosynthesis occurring, but then again starts to level off from 3000lux onwards. This means that at around 3000lux again the light begins not to affect the experiment. Both the graphs are quite similar, each having a period of steep increase/decrease followed by a period where the line levels, and where the light seems not to affect the plants rate of photosynthesis. To understand why this is we must understand the term "limiting factor". A limiting factor is a factor such as light which if there is not enough present will limit the rate of something, in this case the rate of photosynthesis. There are many limiting factors controlling the rate of photosynthesis, such as light, amount of nutrients in the soil, and amount of carbon dioxide in the surrounding air. For the rate of photosynthesis to be at its maximum all these limiting factors must be at an optimum. If one is not then the maximum rate cannot be achieved and will be lowered. (fig 1) Overall from this experiment we have concluded that light intensity is a definite limiting factor to how much a plant photosynthesises. With a very high light intensity the plants are able to photosynthesis well but without the control of other factors it will not be the maximum rate of photosynthesis. Evaluation Overall I feel that the experiment went well and the results produced were reliable fitting in with our prior knowledge of the subject. However if we were to repeat the experiment we may have changed it to improve the accuracy of the results. Firstly when measuring the length of bubbles the reading, especially for the later experiments, could be read inaccurately such was the minute size of bubbles produced. To improve on this we could have measured a set amount of sodium hydrogen carbonate to use during the experiments. This chemical adds the amount of carbon dioxide there is in the water and so would increase the rate of photosynthesis, meaning that the results would not be a small as they were. Also while performing the experiment, some of the oxygen produced from photosynthesis may have dissolved into the water. Some oxygen may have even been used by micro-organisms living on the pond weed. 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 again this amount would be insignificant. A factor that was not controlled and was very present was the temperature. At the high light intensities there would also be a change in temperature in the water. This may have changed my results and so made them unfair. To remedy this situation we could have used a glass block in front of the light, letting in the light but stopping much of the heat getting through. To further this investigation we could have performed further experiments, which would investigate other limiting factors, such as amount of carbon dioxide in the surrounding environment. To investigate this we would keep the distance constant but change the amounts of the sodium hydrogen carbonate therefore changing the amounts of carbon dioxide in the water. The experiment would be set up exactly the same except for a constant distance. Readings could be taken and then compared to the readings taken in this experiment.

The Effect of Altering the Light Intensity on the Rate of Photosynthesis of the Aquatic Plant Elodea 7 of 10 on the basis of 2221 Review.