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The aim of the experiment is to determine what effect light intensity has upon the rate of photosynthesis of Canadian Pondweed (Elodea).

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Claire Shaftoe 10JTe Biology Assessed Practical Introduction- Photosynthesis is the chemical process, which takes place in every green plant to produce food in the form of glucose. Plants use the suns energy to join together water and carbon molecules to make the glucose, which is sent around the plant to be used in respiration. 6CO + 6H O ? C H O + 12O (in the presence of light energy and chlorophyll) Aim- The aim of the experiment is to determine what effect light intensity has upon the rate of photosynthesis of Canadian Pondweed (Elodea). Prediction- I think that as the light intensity increases, the rate of photosynthesis will as well. This is because plants need light energy to photosynthesise, to join water and carbon molecules together to form glucose. If more light energy is available to the plant, then it will be able to photosynthesise at a faster rate. The light provides energy for the reaction to take place, and so if a plant has more light then it should have more energy to use in the reactions, and the rate of reaction should become faster. After a certain point, the rate of reaction will stop increasing and become constant. This will either be because another factor (such as Carbon Dioxide or temperature) ...read more.


* The amount of water must be kept the same because water is needed for the reactions to occur in a plant, and so if there is a lack of water, then reactions will be slower, if they take place at all. Another reason that the amount of water must be kept the same is because when plants do not have enough water, they close the stomata, to prevent further water loss. However, when the stomata are closed, carbon dioxide cannot diffuse into the leaf, which would also slow down the rate of photosynthesis. * Temperature must remain constant because enzymes are used in photosynthesis and the respiration of the plant. Therefore, as the temperature increases so will the rate of reaction of the enzymes, up to a certain point, where the enzymes will be denatured. The temperature could be kept constant by performing the experiment in one session, so that the air temperature should not change enough to affect the water temperature. * The type of plant should be kept the same because different plants have different rates of photosynthesis due to different leaf structures. Even plants of the same species can have slightly different rates of photosynthesis, because there may be more or less chlorophyll in the leaves to absorb light. ...read more.


I repeated these results until I was satisfied that the sizes of the bubbles were the same, or very similar to the rest of the results that I had collected. In a future experiment, a more accurate way of measuring the amount of gas given off would be to measure the volume of gas produced, rather than just counting the bubbles. I would do this by having a scale on the test tube, where the gas collects. Then I could measure how much the water level drops by, or how much more gas there is at the end of the minute than there was at the beginning of the experiment. Another problem was that there were air bubbles trapped in the funnel and on the test tube, from when I had set the equipment up. I tried to release all of the bubbles before the experiment started, but this was not very easy and so some remained, mainly on the edge of the test tube. Although I am almost certain that the bubbles that I counted were from the plant as a result of photosynthesis, it is possible that one or two were the air bubbles that had been there since the beginning. A way to get rid of the bubbles on the test tube could be to use a stirring rod, or something similar to knock them off the edge, so that they rose to the top. ...read more.

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