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An investigation into the effect of light intensity on the rate of photosynthesis of Canadian pondweed (Elodea canadensis)

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An investigation into the effect of light intensity on the rate of photosynthesis of Canadian pondweed (Elodea canadensis) Planning Scientific knowledge and understanding All green plants need to be able to make their own food. They do this by a process called photosynthesis, which means, "making things with light." Photosynthesis is a series of organic chemical reactions by which green plants produce glucose and oxygen from carbon dioxide and water. It occurs only in the presence of light, and takes place in the chloroplasts of green plant cells. Land plants get carbon dioxide from the air. Water plants get carbon dioxide from water (carbon dioxide in the air dissolved into water). Photosynthesis creates oxygen and sugar. Oxygen is released into the air and used by all animals, including humans, in order to respire. Sugar is used by the plant to respire or store them inside their body. The overall chemical equation for photosynthesis can be expressed as: Plants convert the light energy into stored chemical energy. Photosynthesis is possible because green plants contain an energy-capturing substance called chlorophyll. The plant gets its green colour because chlorophyll is green. Light energy drives photosynthesis. The chlorophyll captures the light energy and uses it to build carbohydrates from simple raw materials (water, carbon dioxide and minerals). The raw materials that are needed for photosynthesis provide the element to make up carbohydrates - carbon, hydrogen and oxygen. The carbon dioxide in the air is the source of carbon. Hydrogen and oxygen is taken from water by a process called photolysis. These raw materials enter the plant through its roots and leaves. Both water and carbon dioxide enter the pondweed through their leaves. The rate of photosynthesis is affected by changes in light intensity, temperature and carbon dioxide concentration etc. It may be limited by conditions such as light intensity temperature and carbon dioxide concentration. Light intensity has a more immediate effect on the rate of photosynthesis than any other factor. ...read more.


Set up the equipments as the diagram shows. 3. Cut a stem of pondweed of about 6cm in length. 4. Fill a specimen tube with 0.5% sodium hydrogen carbonate solution, and place into a large beaker contains 20� C water. 5. Connect the end of the pondweed with a lead weight and put it into the test tube. 6. Insert a thermometer into the specimen tube, and take a look at the temperature every frequently to make sure that it keeps constant at 20� C. 7. Set up a lamp at a set distance from the plant, ensuring that this distance is from the filament of the lamp to the actual pondweed, rather than the edge of the beaker. 8. Start the stopwatch, and wait for 5 minutes to allow the pondweed to adapt the new condition. If the bubbles are being produced at a steady rate restart the stopwatch and begin to count the bubbles. After 1 minute, stop the stopwatch and record the result into the table. After another minute, record the result into the table, do the same thing for the third time to get an average result for each distance. 9. Now repeat step 7 and 8 with the other distances. Equipment and materials The Equipment and materials I plan on using are: a. Canadian Pondweed (Elodea canadensis) (being cut in one end about 6cm in length) - used as the object of the investigation b. Desk lamp (40W, 60V) x 1 - used for provide light for the pondweed c. Stop watch x 1 - used for timing d. Metre ruler x 1 - used for setting up the distance between the desk lamp and the pondweed e. Sodium hydrogen carbonate solution (0.5%) - used for provide carbon dioxide for the pondweed f. Specimen tube x 1 - used for filling in with sodium hydrogen carbonate solution and pondweed g. Thermometer x 1 - used for making sure the temperature of the sodium hydrogen carbonate solution stays constant h. ...read more.


For example, I can have light intensity 1.5, light intensity 2.5 etc. I think these additional intermediate are most needed between light intensity 1 and light intensity 3. This is because I got a value which is not on the line of best fit for light intensity 3. I need more information to make the curve between light intensity 1 and light intensity 3 smoother. If I have some different values, it will show very clearly what the whole shape of it. Further work * In the experiment, I only have counted the number of bubbles. It can only show roughly how much oxygen is produced. Because the size of the bubbles may be different slightly, and also the concentration of oxygen in these bubbles may be different as well. A better way to do this is to use an Audus apparatus. It can collect the oxygen gas into a little tube to how much oxygen gas is produced. It is also possible to use a density-metre. To measure the concentration. * If the time allows, find out more data about the rate of reaction in each value. Instead of doing three groups, I can do more groups. For example 4 groups, 5 groups or 6 groups. If I have more values, the mean value is more accurate. * Make sure the temperature is 20 �C all the time. I do not think it is possible because the desk lamp would produce a lot of heat, which would heat the water up. But if I can do it, I will get better results. * Though using distance to calculate the light intensity is one way to get the light intensity, it is not as good as measuring it directly using a . There must be some error when one is setting up the distance. Also it is much easier to use a . * A different species of plant would be very helpful. This plant should also be a water plant. This will be helpful because the plant I am using may be not very healthy. 1 ...read more.

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An excellent and very detailed account demonstrating a thorough understanding of relevant theory.

Marked by teacher Adam Roberts 05/07/2013

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