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Investigating the effects different factors have on the rate of photosynthesis in pondweed.

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Investigating the effects different factors have on the rate of photosynthesis in pondweed. By: Eil�sh Rafferty. 12DG Mrs.Cullen Q) A pupil in a biology class observed that there were large numbers of bubbles around the pondweed in the fish tank on sunny days; however, on the dark mornings fewer bubbles were observed. Devise an investigation to explain this observation. Problem. The problem I intend to investigate is why there were large numbers of bubbles around the pondweed on sunny days and on the dark mornings there were fewer bubbles. These bubbles are oxygen gas and they are present as oxygen is a product of photosynthesis. Photosynthesis is the process by which plants make food, it is a chemical reaction between carbon dioxide and water. Sunlight provides the energy for this process to occur. Chlorophyll is a green pigment present in chloroplasts which enables plants to absorb energy. The equation for photosynthesis is: . Carbon dioxide + water Glucose +oxygen. This equation demonstrates that sunlight/light is needed for photosynthesis and also that oxygen is a product of photosynthesis. Background Knowledge. The rate of photosynthesis is dependent on the following environmental factors: light intensity, temperature, and the availability of carbon dioxide, water, and certain minerals. A shortage of any one of these factors can limit the rate of photosynthesis, and an increase in the particular rate-limiting factor will, up to a point, speed up the process. ...read more.


I need to keep the same piece of pondweed as all plants even if they are of the same species and origin will react differently to any factors, no two plants are the same. The adjustment time will need to be kept the same for each distance as it too will effect the rate that oxygen will be produced, if the plant gets longer to adjust at one distance than another the results will be unfair. Plan. Apparatus. * Lamp. * Meter ruler. * A big Beaker. * Filter funnel * Test tube. * Pondweed. * Water (dissolved carbon dioxide). * Water bath. 1) Collect all apparatus needed. 2) Set up the experiment as follows-: a) Cut some pondweed and set it into the filter funnel. (See diagrams). b) Pour the water (dissolved) carbon dioxide into the beaker, (See diagrams), make sure not to fill the beaker to full as other apparatus still needs to be placed in it and so it will overflow. c) Put pondweed and filter funnel into big beaker. d) Take the test tube fill it with water, turn the test tube upside down over the end of the filter funnel and try not to lose any water from the test tube. (The idea is that any oxygen bubbles produced will float up from the pondweed, be trapped by the funnel where they will go up into the test tube). ...read more.


should account for two bubbles or just one, also some bubbles could have been trapped under the glass and so they wouldn't have been counted. I feel it might have been better to measure the volume of space left at the top of the test tube as you don't have to watch the experiment constantly, although it may be hard to get the test tube turned upside down over the top of the filter funnel without losing water but I still feel that the results might have been more reliable. In this way we could estimate the actual volume of oxygen produced. However I still liked the procedure in which we used to carry out the investigation, as we were kept alert during the experiment because we knew that if we missed counting bubbles that our results would be unfair, the other method would be very boring and I wouldn't feel part of it as the photosynthesis takes place and hence the oxygen is produced, the volume of oxygen gas is measure at the end therefore we wouldn't be doing anything in the experiment, what are we suppose to do whilst the plant is photosynthesising? So I preferred the method we used in comparison to the "measuring the volume method" as I felt I had responsibility and an important role to play in our results being fair. ...read more.

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