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# To investigate the limiting effect of light intensity on photosynthesis.

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Introduction

Aim: To investigate the limiting effect of light intensity on photosynthesis. Prediction: I predict that as the light source (desk lamp) is moved closer to the pondweed (Elodea), the rate of photosynthesis will increase therefore more oxygen will be produced creating more bubbles. I believe this will happen because when the light source is nearer to the plant more of the plants surface area is coming in to contact with the light from the desk lamp therefore more photosynthesis will occur which will mean more oxygen will be produced which will create more bubbles. Plan: Method: I am going to collect my apparatus and set it up as in the diagram, then I am going to fill the beaker with water. I will then set up desk lamp in correct position (eg: 20cm away). ...read more.

Middle

* Keep the desk lamp away from contact with water. * Be careful when using scapular. To make sure the experiment is fair, these things must not change: * The same pondweed must be used every time we change the light distance. * Do the experiment twice for each distance to get an accurate average. * There must only be one variable and that is the distance of the light source from the plant. * Keep the experiment at a constant temperature * Take results after one minute for each individual experiment. Results: Distance of lamp from beaker Number of bubbles observed (Expt 1) Number of bubbles observed (Expt 2) Average Number of bubbles observed Foil around the tube 2 1 1.5 No lamp (no foil) 15 13 14.5 Lamp 20cm away 18 20 19 Lamp 10cm away 34 36 35 Lamp 5cm away 62 61 61.5 Lamp 2cm away 64 63 63.5 Analysis Conclusion: Looking at my results a can see a significant increase in the rate of photosynthesis as the distance decreases. ...read more.

Conclusion

is moved closer to the pondweed (Elodea), the rate of photosynthesis will increase therefore more oxygen will be produced creating more bubbles. Evaluation: I think my method was difficult and I don't think my results are very reliable because counting bubbles is not a very reliable method as some bubbles are bigger than others and it is very difficult to count every bubble. Instead I should have used a gas syringe because this method is more accurate and will make my experiment fairer. I could have also used different light intensity, coloured sheets of plastic over the light to see it that affects the rate of photosynthesis and different plants instead of just using elodea. I could have also repeated my experiment more to make my average results more accurate too because I don't think I have enough results to support a firm conclusion. I have also found some anomalous results on my graph and I think these have occurred because I haven't used a very accurate method. By Kira Rudder ...read more.

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