Photosynthesis Required Practical 6

• What is the aim of the photosynthesis experiment described?

  To investigate the effect of light intensity on the rate of photosynthesis
• How is the rate of photosynthesis measured in this experiment?

  By counting the number of O₂ bubbles formed per minute
• What equipment is needed for the photosynthesis experiment?

  • Boiling tube
  • Freshly cut 10 cm piece of pondweed
  • Light source
  • Ruler
  • Test tube rack
  • Stopwatch
  • 0.2% sodium hydrogen carbonate solution
  • Glass rod
• How far should the boiling tube be placed from the light source initially?

  10 cm
• What should be done with the pondweed before starting the experiment?

  Place the cut pondweed into the boiling tube with the cut end at the top
• How long should the boiling tube be left to rest before starting the count?

  5 minutes
• What should be done after starting the stopwatch?

  Count the number of bubbles produced in one minute
• What steps should be followed for each light intensity/distance in the experiment?

  1. Count bubbles three times.
  2. Take the mean of the counts.
  3. Record results in a table.
• What distances should be tested in the experiment?

  10, 20, 30, and 40 cm
• How should the results be presented after the experiment?

  By plotting a graph of the rate of photosynthesis against light intensity
• What is the relationship between light intensity and distance from the light source according to the experiment?

  Light intensity is inversely proportional to the square of the distance
• What are the potential sources of error in the experiment?

  • Temperature may affect the rate of photosynthesis.
  • Bubbles may form too quickly to be counted accurately.
• What are the potential hazards associated with the experiment?

  • Allergy risk from pondweed.
  • Lamp may get hot.
  • Keep water away from electrical outlets and wiring.