Required Practical 6: Photosynthesis

• What should you be able to describe by the end of the video?

  Investigate the effect of light intensity on photosynthesis
• What additional concept should higher tier students explain?

  How results are affected by the inverse square law
• What are the steps to investigate light intensity's effect on photosynthesis?

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

  It releases very little heat
• What should be placed between a normal light bulb and the boiling tube?

  A beaker of water
• What does sodium hydrogen carbonate solution release?

  Carbon dioxide
• What gas is produced by the pond weed during photosynthesis?

  Oxygen
• How long should the pond weed acclimatize in the boiling tube?

  Five minutes
• What are the two main problems with counting bubbles in the experiment?

  Counting can be inaccurate and bubble sizes vary
• How can the problems with counting bubbles be solved?

  Measure the volume of oxygen produced
• What equipment is used to measure the volume of oxygen produced?

  A measuring cylinder
• What happens to the number of bubbles per minute as the distance from the light source increases?

  • Doubling the distance causes the number of bubbles to fall by a factor of four.
  • From 10 cm to 20 cm, bubbles fall by four times.
  • From 20 cm to 40 cm, bubbles again fall by four times.
• What is the inverse square law in relation to this experiment?

  Light intensity falls by a factor of four when distance doubles
• What is the relationship between light intensity and the number of oxygen bubbles produced?

  More light intensity increases oxygen bubbles
• What should students remember about the required practical?

  It will have plenty of questions in the workbook
• What is the main goal of the experiment described?

  To investigate light intensity's effect on photosynthesis