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 is the first step in the required practical for investigating photosynthesis?

  • Take a boiling tube
  • Place it 10 cm from an LED light source
• Why is an LED light used 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 the light and boiling tube
• What does sodium hydrogen carbonate solution release?

  Carbon dioxide
• What is the purpose of adding pond weed to the boiling tube?

  To observe oxygen production during 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
• What should you do after starting the stopwatch?

  Count the number of bubbles produced in one minute
• How many times should you repeat the bubble count?

  Two more times
• What should you calculate after counting the bubbles?

  The mean number of bubbles produced
• What distances should you test in the experiment?

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

  Too fast to count accurately and varying sizes
• How can you solve the problems with counting bubbles?

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

  A measuring cylinder filled with water
• What happens when you plot the mean number of bubbles against distance?

  The number of bubbles falls by a factor of four
• What does doubling the distance from the light source do to the light intensity?

  It falls by a factor of four
• Why does the number of oxygen bubbles fall when light intensity decreases?

  Less light is available for photosynthesis
• What is the inverse square law in relation to light intensity?

  • Doubling the distance reduces light intensity by four times
  • Affects the rate of photosynthesis
• Where can you find more questions on this practical?

  In the vision workbook
• What should higher tier students be able to explain about the results?

  How they are affected by the inverse square law