Required Practical 6:Photosynthesis

• What is the purpose of the experiment described in the video?

  To investigate the effect of light intensity on the rate of photosynthesis.
• What are the steps involved in investigating the effect of light intensity on photosynthesis?

  • Place a boiling tube 10 cm from an LED light source.
  • Fill the boiling tube with sodium hydrogen carbonate solution.
  • Add a piece of pond weed and acclimatize for 5 minutes.
  • Count the number of oxygen bubbles produced in one minute.
  • Repeat the experiment at distances of 20 cm, 30 cm, and 40 cm.
• Why is an LED light source preferred for this experiment?

  Because they do not release much heat, preventing temperature changes.
• What is the role of sodium hydrogen carbonate solution in the experiment?

  It provides carbon dioxide needed for photosynthesis.
• What gas is produced by the pond weed during photosynthesis?

  Oxygen.
• What are the two main problems encountered when counting bubbles in the experiment?

  • Bubbles can be too fast to count accurately.
  • Bubbles vary in size, leading to inconsistent measurements.
• How can the problems of counting bubbles be solved in the experiment?

  By measuring the volume of oxygen produced using a measuring cylinder.
• What is the relationship between distance from the light source and the rate of photosynthesis?

  • As distance increases, the number of bubbles produced decreases.
  • Doubling the distance causes the number of bubbles to fall by a factor of four.
• What is the inverse square law in the context of this experiment?

  If the distance is doubled, the light intensity falls by a factor of four.
• What should higher tier students be able to explain regarding the results of the experiment?

  How the results are affected by the inverse square law.