Required Practicals

• • Aim: Investigate the effect of light intensity on the rate of photosynthesis using an aquatic organism such as pondweed
• • You will:
  • measure the volume of oxygen produced by the pondweed as the light intensity changes as the light source is moved
  • measure and calculate rates of photosynthesis
  • extract and interpret graphs of photosynthesis rate involving one limiting factor
• • The most commonly used method to measure the rate of photosynthesis is to measure or observe the oxygen released from aquatic plants
• Method

  • Place a piece of pondweed (Elodea or Cabomba are often used), into a beaker of Sodium Hydrobicarbonate
  • Use a light a set distance from the plant
  • Record the number of bubbles observed in three minutes
  • Repeat steps for different distances ( 20cm )
• Improvements

  • Use a gas syringe to collect the volume of gas produced
  • Repeat the experiment at least twice for each distance and calculate the mean number of bubbles
  • Use of a glass tank between lamp and plant to prevent heating of the plant, or using an LED bulb that releases very little heat energy
• Variables

  • Different variables can be investigated using this method. The three diagrams show the setup for 3 independent variables: light, carbon dioxide and temperature
• Results

  • A graph of the independent variable used against the number of bubbles produced per minute can be drawn to see the pattern or trend