Photosynthesis practical

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

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

  How results are affected by the inverse square law
• What type of light source is used in the experiment?

  LED light source
• Why is an LED light preferred for this experiment?

  It doesn't release much 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 is the purpose of adding pond weed to the boiling tube?

  To produce oxygen through photosynthesis
• How long should the pond weed acclimatize in the boiling tube?

  Five minutes
• What gas is produced by the pond weed during photosynthesis?

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

  Count the number of bubbles produced
• How many times should the bubble counting be repeated?

  Two more times
• What is the next step after counting bubbles at 10 cm?

  Repeat the experiment at 20 cm
• What are the distances used in the experiment?

  10 cm, 20 cm, 30 cm, 40 cm
• What are the two main problems with counting bubbles?

  Counting speed and bubble size variation
• 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?

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

  It falls by a factor of four
• What is the relationship between distance and light intensity in this experiment?

  Light intensity falls by a factor of four
• What is the scientific term for the observed relationship in this experiment?

  The inverse square law
• What is necessary for photosynthesis to occur?

  Light
• What should students do to prepare for questions on this practical?

  Refer to the vision workbook
• What are the steps to investigate the effect of light intensity on photosynthesis?

  1. Set up boiling tube 10 cm from LED light.
  2. Fill boiling tube with sodium hydrogen carbonate solution.
  3. Add pond weed and acclimatize for 5 minutes.
  4. Count bubbles produced in one minute.
  5. Repeat at distances of 20 cm, 30 cm, and 40 cm.
  6. Measure volume of oxygen produced if counting bubbles is inaccurate.
• What are the key points of the inverse square law in this experiment?

  • Doubling the distance reduces bubbles by a factor of four.
  • Light intensity decreases as distance increases.
  • Oxygen production decreases with reduced light intensity.