Photosynthesis

• what's the aim of this investigation?

  • Investigate the effect of light intensity on the rate of photosynthesis using an aquatic organism such as pondweed
• what will you do?

  • 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
• what is the most common method to measure the rate of photosynthesis?

  • The most commonly used method to measure the rate of photosynthesis is to measure or observe the oxygen released from aquatic plants
• what factor being investigated can be changed?

  the distance of the lamp
• what's the method?

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


  practical

  
• what are some improvements of the method?

  • 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
• what are the independent variables?

  • light
  • carbon dioxide
  • 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
  • A graph of distance from the lamp against number of bubbles per minute