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Investigation To Find Out How Amount of Light Affects Photosynthesis.

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INVESTIGATION TO FIND OUT HOW AMOUNT OF LIGHT AFFECTS PHOTOSYNTHESIS Introduction: Plants release oxygen as a waste product of photosynthesis. In water plants, this forms bubbles visible in the water, and these bubbles can be encouraged to come out of the cut end of a stem. We are going to find out how rate of bubbling varies with different intensities of light. The test-tube will be subjected to different intensities of light, as the distance that the lamp will be placed form the test-tube will be varied. Hypothesis/Predictions: The higher the concentration of light the greater the rate of photosynthesis. Apparatus List: Test-tube Bench lamp Meter ruler Canadian pondweed 1% Sodium hydrogen carbonate solution Method: 1. Choose a fresh, bright green shoot of Canadian pond weed, and make a sloping cut across its stem to provide a length that would come about 1/2 to 3/4 up a test-tube. Nearly fill the test tube with 1% sodium hydrogen carbonate solution (in affect this is water with lots of Co2 ) 2. Put tube into test tube rack, and place it as close to a bench lamp as possible. Leave it to settle down whilst you construct a table for results. 3. Start close to lamp and move lamp back at 10cm intervals, doing counts at each distance. ...read more.


The temperature of the liquid within the test-tube alters due to the distance of the lamp from the test tube. The rate at which the enzymes involved in photosynthesis catalyse is altered due to the alteration of temperature, which in turn is altered due to the change in light intensity. Plants are autotrophic. They use carbon dioxide, water, minerals and salts to build up carbohydrates. They use sunlight as activation energy for this reaction. Oxygen is given of as a by-product of photosynthesis, so we must be seeing bubbles of oxygen gas in the test tube. To prove that it is oxygen gas that is being given off we can test it by collecting it and testing it with a glowing splint (if the splint relights it is oxygen). The equation for photosynthesis: Carbon Dioxide + Water Glucose + Oxygen 6CO2 + 6H2O C6 H12 O6 + 6O2 The arrows represent light energy from the sun. Photosynthesis occurs generally in leaves, this is why we have taken a bright green shoot (The green colour is made by the chlorophyll pigment which is necessary for photosynthesis and is generally found in leaves) because without the green colour no chlorophyll would be present and so photosynthesis cannot occur. ...read more.


that means that it is possible that the test-tube may have magnified the temperature slightly or that at this time some form of reaction took place and caused the temperature to rise. The reason both of these results are anomalies is because on the graph there is a large gap between 55.6 and 39.6 bubbles, pushing them off the best-fit line. The reason there is an anomaly on the graph to find out how the average number of bubbles is affected by falling light intensity is because; the rate of photosynthesis dramatically drops at one point and the anomalous result is at a point before the drop, that does not fit on the curve. Anomalies on the results table are only because of the plant's rate of photosynthesis, perhaps at a point the plant did not absorb enough carbon dioxide, or was low on glucose and starch in some areas and began to photosynthesise more rapidly than before. Improvements: Putting a clear Perspex cover to absorb heat from the lamp to avoid a change in temperature. Oxygen could have been measured by using a syringe. A black piece of paper could have been used to block background lighting. A different piece of pondweed should have been used for each experiment as the rate of photosynthesis slowly decreases. ...read more.

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