RP - Measuring Rate of Photosynthesis

  • Created by: India.02
  • Created on: 01-05-19 18:05
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  • Required Practical - Measuring rate of photo-synthesis
    • Method
      • 1. A source of white light is placed at a specific distance from the pondweed
      • 2. The pondweed is left to photo-synthesise for a set amount of time - as it does this, oxygen will be released and will collect in the capillary tube
      • 3. At the end of the practical, a syringe is used to draw the gas bubble in a tube alongside a ruler - the length is measured
        • This is proportional to the volume of oxygen produced
      • 4. Any variables that can affect the results should be controlled - the temperature and the time that pondweed is left to photo-synthesise
      • 5. Experiment is repeated twice with the source of light at the same distance and the mean volume of oxygen is calculated
      • 6. Experiment is then repeated with the light source at different distances from the pondweed
    • Apparatus
      • Can be altered to measure the effect of temperature and carbon dioxide on the amount of oxygen produced
        • Test tube can be put in a water bath at a set temperature
        • A measured amount of sodium hydrogen-carbonate can be dissolved in the water - it gives off carbon dioxide
        • Experiment is then repeated with different temperatures and a varied concentration of sodium hydrogen-carbonate
    • Inverse Square Law
      • When the lamp is moved away from the pondweed, the light intensity decreases
      • Light intensity decreases in proportion to the square of the distance
      • The law means that if you halve the distance, the light intensity will be 4x greater
      • If you double the distance, the light intensity will be 4x smaller
      • Light intensity can be measured with 1/d*2


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