Required Practical 6: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 is observed from the cut end of the pond weed?

  Bubbles of gas
• What gas is produced by the pond weed during photosynthesis?

  Oxygen
• What should be done after counting bubbles for one minute?

  Repeat two more times
• What is the next step after calculating the mean number of bubbles?

  Repeat the experiment at different distances
• What distances should the experiment be repeated at?

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

  Too fast to count and varying sizes
• 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 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 scientific principle explains the observed results?

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

  Light
• What are the steps to investigate the effect of light intensity on photosynthesis?

  1. Set up boiling tube with sodium hydrogen carbonate solution.
  2. Place pond weed in the tube.
  3. Position LED light at 10 cm distance.
  4. Acclimatize for five minutes.
  5. Count bubbles produced in one minute.
  6. Repeat at 20 cm, 30 cm, and 40 cm.
  7. Measure volume of oxygen if counting 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.
  • This relationship affects the rate of photosynthesis.