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To investigate the effect of light intensity on the rate of photosynthesis on elodea (pondweed)

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Introduction

Biology Coursework Aim: To investigate the effect of light intensity on the rate of photosynthesis on elodea (pondweed) Prediction: I predict that the light intensity, amount of carbon dioxide and the surface area of the pondweed are all proportional to the rate that photosynthesis will occur and that as they are increased so will the rate of photosynthesis until a certain level is reached.. I think that as the light intensity increases so will the rate of photosynthesis. I think this because green plants need light for the process to occur, as the chlorophyll in plants convert the light into energy (glucose) and the lighter it is the more light can be absorbed by the chlorophyll and so the faster the rate of photosynthesis can occur. I also think that the higher the percentage of carbon dioxide the faster the rate of photosynthesis will occur. I have based this prediction on the fact that the carbon dioxide provides the carbon atoms for the sugar compounds which fuel respiration so the more carbon dioxide the more carbon atoms so the more sugar compounds and the faster the respiration can take place in the photosynthesis process. I also think that the larger the surface area of the elodea the faster the rate of photosynthesis will take place. ...read more.

Middle

1. Fill the boiling tube with 40mls of water. We fill the test tube with water because if water is lacking then the stomata will close up and the carbon dioxide intake will be flawed 2. Add bicarbonate. We add this to our experiment because if it is lacking then it is a limiting factor to the photosynthesis and therefore are results will have an impeding affect on them. 3. Put the elodea into the boiling tube 4. Attach the boiling tube to a clamp stand 5. Measure a distance of 10cm between the foot of the clamp and the lamp 6. Then wait for one minute (until the bubbles are constant) 7. Then time for one minute with the stopwatch counting and recording the number of bubbles produced. 8. Then immediately time for another a minute counting and recording the number of bubbles produced 9. Repeat the last instruction once again 10. Then move the lamp a further 10cms away from the clamp stand 11. Repeat instructions 6 ,7 and 8 12. Then move the lamp a further 10cms away 13. Repeat instructions 6, 7, 8, and 9 but increasing 10cms to the distance with each time until the distance between the clamp stand and lamp is 60cms Diagram: Fair test: To make sure that this experiment was as accurate as possible we had to make sure that it was a fair test. ...read more.

Conclusion

Also in my graph I had no anomalous points, which proves that my results were fairy accurate even though there was hiccups in keeping it a fair test due to the heating of the lamp and the room being light. This may have effected the results we gained however they have not disputed the fact that the closer the lamp was the faster the bubbles were produced. Evaluation: I think that the experiment went well and that the average results for each distance were accurate. I think that there could be numerous improvements on this experiment including calculating the distance between the pondweed and the lamp instead of the foot of the clamp and the lamp. Also you could improve the experiment by collecting the oxygen in upside down test tube. You do this by filling the test tube up with water then turning it upside down then having a delivery tube going from the pondweed into it and as the gas goes in it pushes the water out and so you can measure how much gas you have collected. and we therefore experienced light pollution from other student´┐Żs experiments. This would have had a very marginal effect on my results as a whole, but to eliminate this problem completely, it would have been necessary to perform the experiment in a totally dark room. A further inaccuracy was in the heat generated by the lamp. ...read more.

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