REQUIRED PRACTICAL - Investigating Light Intensity -

• The effect of light intensity on photosynthesis can be investigated in water plants such as Cabomba or Elodea, types of pond weed, which are sold in aquarium shops
• Plants will release bubbles of oxygen, a product of photosynthesis, which can be counted
• Aim: To investigate the effect of light intensity on the rate of photosynthesis
• Method:

  • Set up a lamp with an LED bulb at different distances from the plant in a beaker of water
  • Use an LED bulb to avoid raising the temperature of the water
  • Add sodium hydrogen carbonate (NaHCO3) to the water to supply carbon dioxide to the plant
  • Light intensity is proportional to distance, decreasing as the distance from the bulb increases
• Method

  A lamp with an LED bulb is set up at different distances from the plant in a beaker of water:

  • an LED bulb is best as this will not raise the temperature of the water
  • sodium hydrogen carbonate (NaHCO3) is added to the water to supply the reactant carbon dioxide to the plant
  • the light intensity is proportional to distance - it will decrease as the distance away from the bulb increases.

  
• The bubbles produced over one minute periods are recorded. The rate of photosynthesis is the number of bubbles produced per minute.

  Variables

  • independent variable - distance from the light source/light intensity
  • dependent variable - the number of bubbles produced per minute
  • control variables - concentration of sodium hydrogen carbonate solution, temperature, using the same piece of pondweed each time