Required practical 6: Photosynthesis

• Step 1: take a boiling tube and place it 10cm away from an LED light source (because it emits less heat)
• Step 2: fill the boiling tube with sodium hydrogen carbonate solution which releases carbon dioxide needed for photosynthesis
• Step 3: put a piece of pond weed into the boiling tube with the cut end at the top and leave for 5 minutes (to acclimatise to the conditions of boiling tube)
• Step 4: start a stop watch and count the number of bubble produced in one minute
• Step 5: repeat two more times to calculate the mean number of bubbles produced in one minute
• Step 6: repeat all steps with different distances away from the light (20cm, 40cm, 60cm)
• problems:

  • number of bubbles can be too fast to count accurately or bubbles may not be the same size

  solution: place the pondweed under a funnel and catch bubbles in a measuring cylinder, to measure the volume of oxygen produced