practical

• prac process:


  1. Place a piece of freshly cut pondweed in a boiling tube filled with sodium hydrogen carbonate solution.  
  2. Place the boiling tube 10 cm away from a lamp.
  3. Switch the light on and leave for 5 minutes to let pondweed get used to conditions, bubbles should start appearing from the end of the pondweed.
  4. Start the stopwatch and count and record the number of bubbles produced in 1 minute
  5. Repeat the count at this distance twice more in order to calculate the mean number of bubbles per minute. 
  6. Repeat the experiment with the boiling tube at different distances from the lamp.
• reduce limiting factors in prac:

  • Using an LED bulb as they release less heat.
  • Putting a glass screen between the lamp and plant to prevent the contents of the boiling tube being heated.
• It is also important to control the carbon dioxide concentration by using the same concentration of sodium hydrogen carbonate solution and using the same piece of pondweed/same sized pondweed each time.
• keep temperature of the solution the same throughout the investigations, unaffected by the distance from the lamp, because increasing the temperature will increase the rate of photosynthesis