photosynthesis practicle

• What additional concept should higher tier students explain regarding the results?

  How the results are affected by the inverse square law
• What equipment is used to start the experiment?

  • Boiling tube
  • LED light source
  • Sodium hydrogen carbonate solution
  • Pond weed
• Why is an LED light source preferred for this experiment?


  Because it doesn't release much heat, which could change the temperature of the experiment
• What should you do if using a normal light bulb instead of an LED?


  Place a beaker of water between the light and the boiling tube
• What does sodium hydrogen carbonate solution release that is needed for photosynthesis?


  Carbon dioxide
• What should be done after placing the pond weed in the boiling tube?


  Leave it for five minutes to acclimatize to the conditions
• What gas is produced by the pond weed during photosynthesis?

  Oxygen
• How do you measure the rate of photosynthesis in this experiment?


  By counting the number of bubbles produced in one minute
• What is the problem with counting bubbles in this experiment?


  The number of bubbles can be too fast to count accurately and they are not always the same size
• How can the problems with counting bubbles be solved?

  By measuring the volume of oxygen produced instead of counting bubbles
• What is the procedure for measuring the volume of oxygen produced?


  1. Place the pond weed in a formal.
  2. Catch the bubbles in a measuring cylinder filled with water.
  3. Measure the volume of oxygen produced using the measuring cylinder.
• What happens when you plot the mean number of bubbles or volume of oxygen against the distance from the light source?


  You get a graph showing the relationship between light intensity and photosynthesis rate
• What occurs to the number of bubbles per minute when the distance is doubled?


  The number of bubbles per minute falls by a factor of four
• What is the inverse square law in relation to this experiment?


  If the distance is doubled, the light intensity falls by a factor of four
• Why is light necessary for photosynthesis?


  It is required for the process that produces oxygen bubbles
• What should higher tier students be able to explain regarding the results?

  • How the results are affected by the inverse square law
  • The relationship between light intensity and the rate of photosynthesis