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The aim of this experiment is to investigate the factors affecting photosynthesis in Elodea.

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Photosynthesis The aim of this experiment is to investigate the factors affecting photosynthesis in Elodea. Plants photosynthesise in order to produce energy, in the form of glucose, from sunlight. The light energy from the sun is converted into chemical energy by chlorophyll, contained in the chloroplasts of leaf cells, and is stored in the plant as glucose. The formula for photosynthesis is: Carbon dioxide + water glucose + oxygen 6CO2 + 6H2O C6H12O6 + 6O2 There are many features of the leaf that make it efficient for photosynthesis. There is a large surface area so the chlorophyll can absorb the maximum possible amount of light. In the outside of the epidermis, which is coated with a waterproof waxy cuticle, there are tiny pores called stomata. These allow carbon dioxide to enter the leaf and oxygen to leave. Most of the stomata are in the lower epidermis of the leaf, to reduce the amount of water lost through evaporation. Chlorophyll, which allows photosynthesis to take place, is found in chloroplasts, which are situated mainly in the palisade cells. As the chloroplasts can move around the palisade cells they are able to concentrate nearest the light at the surface. The palisade cells are packed tightly together near the upper surface of the leaf. The spongy mesophyll cells are situated below them. These cells have large air spaces to allow carbon dioxide to diffuse quickly to the palisade cells for photosynthesis, and for the oxygen produced by photosynthesis to quickly be able to diffuse out of the leaf. The vein of a leaf is made up of the xylem and the phloem tubes. Water and mineral salts are transported to the palisade cells by the xylem, to be used for photosynthesis. Sugars produced by photosynthesis are transported away from the leaf through the phloem tubes. During photosynthesis plants produce carbohydrates. These are made up of carbon, hydrogen, and oxygen. ...read more.


Preliminary work For my preliminary work I am going to find the maximum and minimum light intensity until photosynthesis is no longer affected. I am going to use the equipment in the diagram, and follow the method below. Method: - 1. Begin with the lamp switched off. Start the stop-clock and for 1 minute count the number of bubbles given off from the Elodea. These are bubbles of oxygen. This is called the control. 2. Begin with the lamp switched on, 1 metre away from the elodea. Start the stop-clock. For 1 minute count the number of bubbles given off from the Elodea. 3. If the number of bubbles is lower than the control figure, repeat the experiment at a greater distance of the lamp from the Elodea. Continue to do this at 10cm intervals until the number of bubbles released is the same as the control. 4. If the number of bubbles is the same as the control, repeat the experiment decreasing the distance of the lamp from the Elodea at 10cm intervals. Continue to do this until the number of bubbles is less than the control. The value 10cm lower than the last place equivalent to the control is the minimum light intensity. 5. Place the lamp 20cm from the Elodea. Start the stop-clock and count the number of bubbles released from the Elodea for 1 minute. Decrease the distance of the lamp from the elodea at 2cm intervals, and repeat the experiment at each distance. When the number of bubbles released starts to decrease, the previous value was the maximum light intensity because the chloroplasts in the Elodea have been damaged. I will repeat the experiment 3 times at each distance so I can take an average of the results. Preliminary results: - Distance of lamp from Elodea (cm) Number of bubbles released from elodea Trial 1 Trial 2 Trial 3 Average Control (no lamp) ...read more.


Controlling the other variables better would also have made my results more accurate. For example, I could have made sure the light intensity was the same each time by measuring it in lux, with a light meter. I could have used Perspex to reduce heat instead of using a beaker of water, as this may have been more effective, and would have also allowed me to continue to move my lamp right up to the beaker. Also, to improve the reliability of my procedure I could collect and measure the volume of gas released in a gas syringe instead of counting bubbles. I could also use a measuring cylinder filled with water and record how much water was displaced by oxygen. This would give me more exact results, as the bubbles may not all be of the same size, therefore allowing me to make a more detailed conclusion. The light from other experiments being carried out in the room could have interfered with my experiment, so an improvement would be to carry out the experiment in a room where the only lighting is from the single lamp, and where there are no other experiments being carried out simultaneously. When doing the experiment I made the assumption that the level of carbon dioxide in the air was always 0.03%. Another improvement I could have made would have been to measure the percentage of carbon dioxide, and make sure it was always the same. To extend this enquiry I could carry out the experiment at different masses of elodea, to see if the mass of the plant affects the relationship between light intensity and rate of photosynthesis. I could also take all the leaves off the plant, and see how that affects the rate of photosynthesis. To allow me to plot more points on my graph I could take measurements at more regular intervals. Using Perspex instead of a beaker of water would have allowed me a larger range of results, as I would have been able to continue to move the lamp right up to the beaker containing the Elodea. Zo� Twigg ...read more.

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