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Investigate a factor that affects the rate of photosynthesis.

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Aim: To investigate a factor that affects the rate of photosynthesis. Introduction: A measured piece of pondweed will be cut and placed into a beaker containing measured amounts of water and sodium hydrogen carbonate. A lamp will be shined on to the pondweed and the amount of bubbles that are produced from the plant will be counted. The lamp will be adjusted to different distances from the plant to try and obtain differing results. The point of this experiment is to find out how light intensity affects the rate of photosynthesis. The equation for photosynthesis is: 6CO2 + 6H2O = C6H12O6 + 6O2 Carbon Dioxide + Water (light energy) Glucose + Oxygen Light intensity will be the controlled variable looked at in this investigation. Increasing or decreasing the distance from the light source to the plant varies the light intensity. Fixed Variables Why the rate of photosynthesis increases or decreased from the amount of light energy absorbed is what is being investigated in this experiment. Pigments in the leaf such as chlorophyll absorb light energy. Chlorophyll easily absorbs blue light, in the 400-450 nm range, and also easily absorbs red light in the 650-700 nm range. ...read more.


But since the circle is expanding, the circumference increases and the same light energy is distributed along a greater surface. Preliminary investigation Before carrying out the real experiment, we carried out a preliminary investigation to see which factors we can improve to increase the effectiveness of the experiment. The most effective length of elodea was 10cm. This was because there is a larger surface area for photosynthesis to occur. The best light intensities were 5cm, 10cm, 15cm, 20cm and 25cm. This gave a wide range but not so wide that they would produce unreliable results. We also worked out that turning a measuring cylinder full of water upside down and put it over the top of the elodea in a beaker, better results were attained because less bubble escaped. Clipping the elodea to the bottom of the measuring cylinder helped to keep it from rising and therefore difficult to read the measurements. Method 1) Set up the apparatus as shown (in the diagram on separate paper) but leaving out the pondweed, measuring cylinder, test tube, water, and the sodium hydrogen carbonate. 2) Fill the beaker with 200 cm3 of water and 50 cm3 of NaHCO3. ...read more.


The CO2 content probably would not have affected the results further as we put much NaHCO3 into the water. Evaluation I think that the results we obtained were very reliable. There was only one anomaly showing that results were accurately recorded. I think that my method of carrying out the experiment was thorough but if I carried out this investigation again then I would carry out more preliminary work to ascertain why the results that our class gathered were unreliable and why our pondweed did not photosynthesise effectively, causing us to rely on secondary results. To extend this investigation, I would look at other limiting factors of photosynthesis and try to understand the link between the all. I could also attempt to look at the effects of different colours in light and see which colours worked more effectively than others. To improve the experiment, I could of attempted to block out foreign light better, as this may have affected my results. I could also look at better ways of controlling the temperature, maybe by using a beaker of water, as this would absorb heat but also is transparent. I would have to analyse this carefully however, as water can refract light and this would take me further into the effects of different light and light colours. ...read more.

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