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Photosynthetic rate and light intensity.

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Biology Coursework-Photosynthetic Rate and Light Intensity PLAN Aim - to investigate the effect of light intensity on the rate of photosynthesis in a plant. Prediction - Plant cells use light to help them to make food by photosynthesis. They trap the energy in the sunlight and use it to convert carbon dioxide and water into sugars. The chemical reaction that takes place is: Light energy 6 CO2 + 6 H2O C6 H12 O6 + 6 O2 (from air (from soil Chlorophyll in sugar via stomata) via root hairs Chloroplasts and xylem) Substrates Products All plants need light to photosynthesise otherwise they will die. The photosynthetic rate is affected by the light intensity because when the light falls on to the chloroplasts on the leaf, it is trapped by the chlorophyll and therefore makes energy available for chemical reactions in the plant. So as the light from the bulb shines on to the plant, more energy is absorbed and is available for chemical reactions, more photosynthesis takes place. From this information, I predict that as I increase the light intensity from the bulb, the photosynthetic rate will also increase at a directly proportional rate until it reaches a point where increasing the light intensity will no longer affect the photosynthetic rate. ...read more.


In this experiment, I am investigating why the rate of photosynthesis increases or decreases with the amount of light energy absorbed. I will keep this constant by using the same lamp during the experiment. ==>Carbon Dioxide-This can affect the photosynthetic rate because the more of it in the air, the more that can diffuse into the Elodea. To keep this variable constant, I need to put a fixed amount of sodium hydrogen carbonate into the boiling tube along with the water and the plant. OBTAINING EVIDENCE I carried out my plan to the best of my ability and these are the results I came up with: Independent Variable (Distance - mm) 1st Dependant Variable reading (O2 bubbles) 2nd Dependant Variable reading (O2 bubbles) 3rd Dependant Variable reading (O2 bubbles) Average Dependant Variable 20 10 12 11 11 40 8 7 8 7.67 60 5 5 6 5.33 80 3 5 5 4.33 100 1 3 3 2.33 I used my three sets of results, which are in the centre three boxes, to create average results in the column on the far right. I am going to use theses results to draw my graphs. ...read more.


I did not really allow time for the elodea to equilibrate to the light intensity and so the number of O2 bubbles was probably less than expected. I was also unsure as to when to start my timing, whether it be as soon as I see a bubble produced or just at a random point but whatever I did, I would have to keep constant to make my results reliable. I decided upon doing when I see a bubble rise so then I would know that the Elodea has at least equilibrated a little bit. To improve the quality of the data, I could perform the experiment using a syringe and capillary tube, so that the bubbles form one bubble and then I can measure the volume of the bubble. I can do this because I know the size of the tube so it just depends on the length. This is how it would be set up: If I was to do this again, I would make sure I give the plant the time it needs to equilibrate and use the improvements I suggested. I would maybe also extend my range of results to a further distance, although the reason I didn't this time was because the number of oxygen bubbles produced was so low I didn't think anymore would be produced at a lower light intensity. ...read more.

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