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An investigation into the effect of light intensity on the rate of photosynthesis on a piece of elodea

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An investigation into the effect of light intensity on the rate of photosynthesis on a piece of elodea Plan: Method: 1) First I will put some water into a boiling tube and add 5 spatulas of Sodium Hydrogen Carbonate. I will add 5 spatulas of Sodium Hydrogen Carbonate as it reacts with water and forms carbon dioxide; also I have so much so that I have carbon dioxide in excess. 2) Then I will cut off 5cm of elodea and place it into the boiling tube. 3) Thirdly I will place the boiling tube in a test tube holder 5cm in front of the light source. 4) Then I will count the number of oxygen bubbles that rise to the top in 5 minutes. 5) I will repeat the experiment 2 more times, so I have a total of three results to work out my average as well as that it makes it a fair test 6) Also I will move the boiling tube 5cm away from the light source a total of 4 times. Equipment: Sodium Hydrogen Carbonate Spatula Boiling Tube Test Tube Rack Lamp Water Scissors Ruler Elodea Stopwatch Diagram: Prediction: I predict that as the distance from the light increases the average number of bubbles produced in 5 minutes will decrease. I think this because light plays a very important part in photosynthesis. Carbon Dioxide + Water Glucose + Oxygen As can be seen by the above equation light is the main source of energy for photosynthesis. ...read more.


This graph shows the effect of the temperature on the rate of photosynthesis Chloroplast is the most important organelle in plants for photosynthesis. It is found in mesophyll cells and it contains green chemical called chlorophyll which converts energy from the sun into chemical energy which is used in photosynthesis. The chlorophyll absorbs all white light apart from green, which it reflects as the chlorophyll is green. Light is very important for photosynthesis. It is the main supply of energy. The speed that light increases the rate of photosynthesis at, depends on the colour of the light from the spectrum. The rate of photosynthesis is at its best when there is red, orange or yellow light present. That is why in autumn the rate is very low because the leaves are a red, orange or yellow in colour, because the chlorophyll pigment has broken down leaving the more weaker chemicals like xanthophyll which reflect the red, orange and yellow instead of absorbing it. Also as photosynthesis is at its best in red, orange and yellow light it is very poor in green, as the chlorophyll is normally green in spring and summer, when light intensity is at its highest, therefore it reflects the light. As well as green light the rate of photosynthesis is poor in blue and purple light, but not as slow as green light. This is because the blue and purple are very close to the green light therefore it is not as good as red or orange light. ...read more.


As well as that I would have rinsed out the boiling tube a cleaned the spatula so that there is no contamination and that the pH of the water isn't affected. Furthermore I would get more than one person counting the number of bubbles that are produced and then take an average of what they get for each experiment or I would set up a computer so that it counts the number of bubbles that are produced, however that it a lot more complicated. As well at that if I do the experiment again I would check that the light is working properly and that it is shining as brightly as possible. Also next time I would do the experiment in a trough and have the light shining over the top so that it has only one medium to travel through and less light it lost due to reflection. An alternative experiment that I could use is to test the pH of the sodium hydrogen carbonate solution at the start and end of the experiment. For this experiment I would add 0.5 grams of sodium hydrogen carbonate into a trough of water. I would then stir the solution and take the pH by using litmus paper or universal indicator, it should be pH14 or thereabouts. I would then add the piece of elodea. I would then place the lamp so that it shines down on the plant limiting the amount of light that is reflected. After 20 minutes I would check the pH once again and the closer it is to pH7 the more it has been photosynthesising. ?? ?? ?? ?? Nilesh Mistry 11SD ...read more.

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