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The affect of Light on Photosynthesis.

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Introduction

Photosynthesis Investigation The affect of Light on Photosynthesis Diagram Equation for photosynthesis :- Sunlight + Chlorophyll Carbon Dioxide + Water Glucose + Oxygen 6CO2 + 6H2O C6H12O6 + 6O2 Plan I am going to investigate the affect of light on photosynthesis. To do this I will carry out the same experiment as I did in my preliminary. I shall set up my apparatus, as shown in the diagram, and measure between the 250 watt lamp and the beaker. I will put marks at 20cm, 40cm, 60cm, 80cm and 100cm from the lamp. When the beaker and contained apparatus are at each point, I will time for 2 minutes and record the number of oxygen bubbles released from the Elodea stem. To see exactly how much oxygen is produced at each point, I will collect the oxygen in a cylindrical measuring tube or similar. I shall start by recording bubbles and collecting oxygen at the 20cm mark. This should get the elodea to start photosynthesising straight away, as opposed to starting at 100cm and waiting a long time for it to just start photosynthesising. ...read more.

Middle

There are a few variables in this experiment. They include water temperature, carbon dioxide in the water, distance the apparatus is from the lamp, and the piece of elodea. I must constantly check the temperature of the water in the boiling tube, as it is an important variable and must be kept the same throughout the experiment. This is why I am going to use a thermometer. If the water temperature in the boiling tube drops or rises significantly, the test will be unfair. This is why I am going fill the beaker with water, as it acts like an insulator. I found this out in my preliminary experiment. The water in the boiling tube does not suffer from great heat loss, or gain, because the insulating water around it, in the beaker, prevents this. This way I can control the water temperature and keep this variable the same. When I do the experiment, I will do it all in one go, and so I shall be using the same piece of elodea plant and water throughout the experiment. ...read more.

Conclusion

This describes the rise of the line in my predicted graph. The reason I have levelled the line out, is because the elodea will eventually stop photosynthesising at faster rates, even though the light intensity may be increasing. This is because the CO2 and water temperature are staying the same. (the CO2 level will probably decrease a tiny fraction throughout the experiment) If I increase the light intensity to such a great point the elodea stops photosynthesising, it means I will need to increase the temperature and CO2 level. This is because the CO2 and temperature are limiting factors in my experiment. As I must keep them the same, the elodea will stop photosynthesising more rapidly and stay at the same rate. In order to help me make a prediction, I read pages 12, 13 and 14 of the CGP revision booklet for biology. I also used a science prompt sheet, provided to me by my biology teacher, to help me structure my plan. Included with my plan on separate sheets, is my preliminary experiment method, results and observations. Tom Sharp, Biology, 11-4 ...read more.

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