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Investigating the effect of light

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Investigating the effect of light intensity on photosynthesis in a pondweed Aim: To investigate how the rate of photosynthesis changes at different light intensities, with a pondweed. Prediction: I predict that the oxygen bubbles will decrease when the lamp is further away from the measuring cylinder, because light intensity is a factor of photosynthesis. The plant may stop photosynthesising when the pondweed is at the furthest distance from the lamp (8cm). Without light, the plant will stop the photosynthesising process, because, light is a limited factor. However once a particular light intensity is reached the rate of photosynthesis stays constant, even if the light intensity is the greatest. If I plot distance of the lamp, against the number of bubbles per 2 minuets, I will get a straight linear graph which will not go through the origin. Introduction: Photosynthesis is the process by which green plants use light to synthesize organic compounds from carbon dioxide and water. In the process oxygen and water are released. The glucose produced in the photosynthesis reaction can be converted to sucrose and carried to other parts of the plant in phloem vessels. ...read more.


* Add a spatula full of sodium bicarbonate. * Pick a pondweed that has a healthy green stem. * Put a paper clip at the end of the pondweed, to make sure that the pondweed stays down. * Place the lamp next the measuring cylinder, measure out 5 cm (this is my first measurements). * Wait till the pondweed starts photosynthesising. * When there is a steady pace of bubbles, start timing and counting. * Time the bubbles for 3 minuets and record the results. * Repeat this with 8 cm, 11 cm, 14 cm, and 17 cm. * Repeat this 3 more times so you get 3 sets of results. Diagram: Table of results: Experiment 1 Distance (cm) Number of bubbles In 1 min Temperature (�C) 0 11 32 2 9 32 4 4 32 6 2 32 8 0 32 Experiment 2 Distance (cm) Number of bubbles In 1 min Temperature (�C) 0 11 30 2 8 32 4 3 32 6 1 32 8 0 32 Experiment 3 Distance (cm) Number of bubbles In 1 min Temperature (�C) 0 13 31 2 8 32 4 3 32 6 1 32 8 0 32 *The Rate of Photosynthesis is the number of seconds it takes for 1 bubble of Oxygen (O2) ...read more.


I have investigated enough distances, because 5 measurements are the average amount of distances in one experiment. I have controlled all my variables - Input variables was the light intensity, the output variable was the measurements and the control were, the same time, around the same temperature and the direction of the light had to face the same way. Temperature was a tricky one to control but because is a limiting factor and might change the rate of photosynthesis. However this was alright in my experiments because there was no great range of temperature changing. There are many other further work I could of done for this experiment apart from changing the distances from the lamp and the measuring cylinder, you can change the light intensity by maybe changing the watts in the light bulb, changing the colour of the light by putting different transparent coloured paper, changing the pondweed by finding a pond weed after every experiment, changing the temperature by using a water bath and heating it to a certain temperature, this would be hard to control. Changing the amount of carbon dioxide by adding a certain amount of sodium bicarbonate, and many more but this is all that I can think about. ...read more.

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