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# An Experiment to Investigate Factors Affecting the Rate of Photosynthesis

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Introduction

An Experiment to Investigate Factors Affecting the Rate of Photosynthesis In this investigation I will be looking at how the rate of photosynthesis is affected in Canadian pond weed by light intensity. Photosynthesis requires 5 things: Carbon dioxide, water, chlorophyll, light and warmth, these are all called limiting factors. A limiting factor is a factor that determines the rate of a reaction. I will set up the experiment by filling a test tube with water and putting some pond weed in it. I will then turn the test tube upside down and place it in a beaker. I will use a lamp for the light source and to collect the result data I will count the number of bubbles given off by the pond weed per minuet. In this graph the rate of photosynthesis increases proportionally to the light intensity. To make the experiment a fair test I must ensure that all the key variables are equal apart from the light intensity. The most common biological variables that could effect the experiment are temperature, pH, light intensity, the amount of carbon dioxide present, Light colour, minerals in the water, chemicals in the water, Health of plant, size of plant and the amount of water . I will be investigating the light intensity. ...read more.

Middle

Apparatus Beaker to place the boiling tube in (filled half way with water) Boiling tube to put pond weed in (filled to the brim with water) Bench lamp for the light source A piece of pond weed about 10cm long 1 m ruler to use to measure the different distances to place the lamp Water to put in the boiling tube and beaker. Method 1. Draw up a result table like this. A table showing the number of bubbles given off/minuet to the amount of light intensity. 2. First cut a small piece of pond weed about 10 cm long and put it into a boiling tube with the cut end facing up. 3. Then fill a large beaker half full of water. 4. From the beaker with use of a 1m ruler mark on the work surface 10, 30,50,75 and 100cm which indicates the different distances to place the lamp. Once you've measured the points do not move the beaker 5. Fill the boiling tube with the pond weed in it up to the brim with water 6. Place your thumb over the end of the boiling tube so no water comes out and submerge it in the beaker half full of water. Take your thumb off and make sure that the boiling tube stands up rite. ...read more.

Conclusion

My results are correct because they solve the experiment and make sense. Evaluating My Evidence My results were pretty good because they were not just random numbers but numbers, which I could take good readings from, and draw a good quality graph. My first results were more consistent than the other 4 results but the other 4 results had greater values. There also my have been a few sources of error in the experiment, such as the health of my pond weed which might effect its ability to photosynthesis, the heating of the water from the light and the light from other peoples experiment effecting mine. My conclusion is only valid over the range of values investigated i.e. 10cm-100cm and for the particular organisms and materials used in this experiment. To improve the reliability of the experiment I could do the experiment in a room by myself so my experiment doesn't get effected by others, I could take a wider range of values, use a more accurate way of knowing the amount of bubbles or amount gas given off and I could investigate with other species of plant. Some further work I could carry out to provide additional and further evidence for the experiment would be to take more readings from the experiment and draw up a larger graph so it would be easier to make out the results and there would be more of them to make the experiment more accurate. ...read more.

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