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Test the prediction that the closer the lamp is to a piece of pondweed in a tube of water the less amount of oxygen will be produced.

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Introduction

Photosynthesis Investigation Aim- Our aim in this investigation is to test the prediction that the closer the lamp is to a piece of pondweed in a tube of water the less amount of oxygen will be produced. Scientific Knowledge: The equation for photosynthesis: Photosynthesis is a chemical reaction occurring in the leaves of green plants. Using the energy from sunlight, it changes carbon dioxide and water into glucose and oxygen. Oxygen is a 'waste' product of photosynthesis. Glucose can be converted to sucrose and carried to other parts of the plant in phloem vessels. Glucose can also be converted into starch and stored (the starch can later be turned back into glucose and used in respiration). A cross section of a leaf Photosynthesis happens in cells in the middle of the leaf. These cells contain tiny bodies called chloroplasts; these contain a green chemical called chlorophyll. Chlorophyll is used to convert light energy into chemical energy. The intensity of light falling on the plant is inversely proportional to the distance, which is called the inverse square law. Doubling the distance between the lamp and the plant reduces the light intensity received by the plant by one quarter. Equation: By trebling the distance between the lamp and the plant reduces the light intensity received by the plant by one ninth. ...read more.

Middle

to use as a light shield for unwanted light Lead strip 1)Add, to 200cm3 of "pond" water in a beaker, one spatula full of sodium carbonate. 2)Fill a boiling tube with this "pond" water. 1) Cut a sprig of Elodea crispa, 5 cm long. 2) Wrap the strip of lead round the top of the sprig. 3) Place the sprig, cut end uppermost, into the boiling tube full of "pond" water 4) Add a few drops of detergent to the contents of the boiling tube. 5) Place the boiling tube in a beaker of water (this will act as a heat shield) 6) Place the thermometer in the water in the beaker. (Record the temperature) 7) Allow the plant to produce a steady stream of bubbles. 8) Shield the set up from unwanted light. 9) Set up the 200w lamp at the furthest distance investigated. (Measure the distance) 10) Allow the plant time to adjust to the new conditions. 11) Count the number of bubbles produced in a known period e.g. 5-10 mins. 12) Measure and record the temperature of the water in the beaker. 13) Repeat these measurements. 14) Repeat steps 11-15 for a range of closer distances. Prediction- I predict from our aim that the closer the lamp from the pondweed the More Bubble or oxygen will be produced. ...read more.

Conclusion

If I was to do the experiment again I would block light coming from the sun and try out the experiment 3 times (excluding other attempts) 1. .......... At a cold room. 2. .......... At room temperature without the heating on 3. And at a fairly hot room. so we can see that if the results are same as now when trying it other ways/ using different variables. The most important problem in this experiment was the distance between the light sources and the Pondweed were not measured to a very high degree of accuracy, especially when you note the fact that the distance should have been measured exactly from the filament of the light bulb to the centre of the plant A further inaccuracy was in the heat generated by the lamp. As I have earlier described, temperature has a very noticeable effect on the rate of photosynthesis, and so any increase in the temperature of the pond water would have had serious effects on the accuracy of my results. To ensure that this does not happen again I would monitor the temperature of the water before and after every reading, to check that the temperature rises or not Overall I feel my experiment was not as accurate as it could have been, however I believe it was accurate enough to support and justify my aim in this investigation. Sarwar Hussain 7.12.2003 99228 ...read more.

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