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Do different coloured wavelengths of light affect the rate of photosynthesis in Canadian Pond Weed?

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Introduction

Do different coloured wavelengths of light affect the rate of photosynthesis in Canadian Pond Weed? Aim; For the aim of this experiment I am trying to discover if different coloured wavelengths of light affect the speed of photosynthesis in Canadian pond weed either speeding up the rate of photosynthesis or prolonging its effects, or even in some places stopping it take place completely. Prediction; I predict that the different wavelengths of coloured light will affect the rate of photosynthesis, for example I believe that when there is a green filter on the light there will be a very slow rate of photosynthesis, almost no reaction at all because pond weed is green and so this shows me that pond weed does not absorb green light it refracts it yet absorbs all the other coloured wavelengths. I also believe that photosynthesis will not occur very fast with a similar colour to green such as yellow as these are next to each other in the colour spectrum. I believe that photosynthesis will react much faster with colours at the end of the spectrum such as red and blue as they are the two extremes of the colour spectrum, infrared and ultra violet. As these two coloured wavelengths are the furthest away from the green wavelength I believe they will increase the rate of photosynthesis in the pondweed. The light wavelength diagram shown below emphasises that infrared and ultra violet are the two coloured wavelengths of light furthest away from the green coloured wavelength. ...read more.

Middle

test tube stand * A spatula * A Stopwatch Method; Firstly we had many practice experiments just to get used to using the pond weed and giving us a chance to discover some variables that we could change for the practical this coursework is based on. One of these experiments was a change of temperature to see if that affected the rate of photosynthesis this was a very difficult experiment as we did no have access to an electronic water bath and so had to control the temperature by using a Bunsen burner which was very challenging so we were not advised to use temperature adjustments in this experiment but to keep the whole experiment at room temperature. We then did a final practice experiment which was going to be the same as the practical this coursework is based on. In this experiment I did encounter some problems but I did overcome them so the method for the final practical is written below. I collected four samples of pond weed each of six centimetres in length and placed them in a beaker. I then collected four boiling tubes and filled them with water and placed one of the four different coloured filters round each tube. I then collected a lamp and positioned it on the first of the four boiling tubes. I took one of the samples of pondweed and cut of a very small section from one end. ...read more.

Conclusion

To solve this problem I would surround the experiment with a reflective material such as tin foil which will stop light being lost and unfiltered light coming into contact with the pondweed. Secondly the temperature was the second problem I faced. With the temperature not being at a constant the results weren't accurate. The temperature also affected the rate of the reaction. I would solve this problem by completing the experiment in a room where the temperature could be kept at a constant thus recording more accurate results. The third and final problem I encountered was the quality of the filters I used. As the filters weren't a very good quality they may have let through some other wavelengths of light. This would have affected my results as if other wavelengths of light were aloud to pass through rather than just the filtered light it may have sped up or slowed down the rate of the reaction. To solve this problem I would use top of the range filters that only allow through the correct colour wavelength. There was one anomaly which was the lack of bubbles the red filter produced, although the bubbles were very large the amount of bubbles was disappointing compared to what my teacher said we should expect. This could have been due to several things such as a poor piece of pondweed or a very poor quality filter. I believe that I could have improved the coursework by spending more time on writing up the coursework and by doing more detailed practical experiments in the lesson time provided. Tim Shipway 11P ...read more.

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