Light Intensity and Photosynthesis

• Photosynthetic rate


  The rate at which plants take in carbon dioxide, water and the energy from sunlight to produce glucose and oxygen
• Light intensity


  A factor that typically increases the rate of photosynthesis

  
• Distance from light source


  The independent variable or factor that is changed in this experiment to investigate photosynthesis

  
• LED light source


  Is used as it releases less heat compared with other light bulbs

  
• Temperature


  A variable that should be controlled in this experiment to ensure the results are valid
• Sodium hydrogen carbonate


  Added to the water to supply the pondweed with a controlled source of carbon dioxide

  
• Pondweed


  A species of aquatic plant such as Cabomba or Elodea

  
• Acclimatise


  Allow the pondweed time to settle during each test before recording data to ensure results are valid
• Bubbles of gas


  The pondweed should release oxygen bubbles that can be counted as a measure of photosynthetic rate
• Number of oxygen bubbles


  The dependent variable or factor that is measured in this experiment to investigate photosynthesis

  
• Mean average


  The total sum of the data values divided by the number of times the data was recorded

  
• Volume of oxygen gas


  A more accurate experiment would be to collect the oxygen in an inverted measuring cylinder and record the volume

  
• Expected results


  As distance from the light source doubles, the number of bubbles per minute should decrease by a factor of four

  
• Inverse-square law


  Light intensity is inversely proportional to the square of the distance from a light source

  
• Inversely proportional relationship


  As the distance of light from a plant increases, the light intensity decreases

  
• Water bath


  A container of water heated to a given temperature for control purposes

  
• Examples of other control variables

  To ensure the results are valid the volume, concentration, external light and pondweed variety should be controlled