B4: Bioenergtics

• 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 count be repeated?

  Two more times
• What is a problem with counting bubbles in this experiment?

  Bubbles can be too fast to count accurately
• What is another issue with counting bubbles?

  Bubbles are not always the same size
• 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 when you plot the mean number of bubbles against distance?

  It shows a decrease in bubbles with distance
• What happens to the number of bubbles when the distance is doubled?

  Falls by a factor of four
• What is the scientific term for the relationship observed in the experiment?

  The inverse square law
• 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 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 for 20 cm, 30 cm, and 40 cm distances.
  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.