6: photosynthesis

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

  Investigate the effect of light intensity
• What is the purpose of using an LED light source in the experiment?

  It doesn't release much heat
• What should you do if using a normal light bulb?

  Place a beaker of water between them
• What does sodium hydrogen carbonate solution release?

  Carbon dioxide
• Why do we leave the pond weed for five minutes?

  To acclimatize to the conditions
• 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
• What is a problem with counting bubbles in the experiment?

  Bubbles can be too fast to count accurately
• How can you solve the problem of counting bubbles?

  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 the distance increases?

  It falls by a factor of four
• What is the inverse square law in relation to this experiment?

  Doubling the distance reduces light intensity by four
• Why does light intensity affect the rate of photosynthesis?

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

  1. Place a boiling tube 10 cm from an LED light.
  2. Fill the 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 main problems with counting bubbles in the experiment?

  • Bubbles can be too fast to count accurately.
  • Bubbles vary in size, affecting measurement.
• What is the relationship between distance and light intensity in this experiment?

  • Doubling the distance reduces light intensity by a factor of four.
  • This causes the number of oxygen bubbles to fall by the same factor.