How Light Intensity Affects the Rate of Photosynthesis

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GCSE Biology Coursework

How Light Intensity Affects the Rate of Photosynthesis

Aim:

‘To determine whether or not different light intensities affect the rate of photosynthesis in Canadian Pondweed’

Equation:         Sunlight

Carbon Dioxide + Water                    Oxygen + Glucose

                                             Chlorophyll

          6CO2                 6H20                                    602       C6H12O6

Prediction:

Seeing as the more light a plant got, within reason, the faster a plant would photosynthesise. Thus, I expect that the higher the light intensity, the higher the rate of photosynthesis. I also predict that as light intensity increases, the rate of photosynthesis will increase at a relative rate until the maximum level of light, at which point the level of increase in photosynthesis will decrease and eventually even out, as a limiting factor, probable temperature, will limit it at this point.

Preliminary Experiment:

In order to attain an accurate experiment, I did a preliminary experiment to determine an appropriate range of distances as to how far my lamp would be placed from the plant. The further away the lamp, the less the light intensity.

The results are:-

Although this is not a very accurate way of measuring the rate of photosynthesis as all I am doing is physically counting the bubbles coming off the pondweed and relying on them all being the same size, it was the best method I could manage with the equipment I had. This preliminary experiment will allow me to compare my 2 main experiments and give me a point of origin to compare and check no unknown variables have happened in the next experiments. The preliminary also told me that the outer ranges, 40 and 5, tell me little so although they are justified, it would be better to take readings towards the middle of the range. So I will take readings 5, 10, 20, 25, 30, 35.

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Method:

Apparatus: Pond Weed, Beaker, Thermometer, Water, Stopwatch,

               Sodium Bicarbonate, Scissors, Lamp, Paper Clips.

After collecting some pondweed of about 5cm in length, I filled a beaker of water and placed the pondweed in it along with some Sodium Bicarbonate to help keep the Carbon Dioxide levels in the water constant. Using the thermometer, I record the temperature of the water at the start and end of the experiment so that the results are all fair. Next, I set up the lamp at the first distance and make sure it is at the ...

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