evolution of oxygen from water plant

• what is this practical also known as

  how the rate of photosynthesis may be affected by light intensity
• method (9)


  1. place pondweed in beaker of water+ensure gas syringe empty
  2. add sodium hydrogen carbonate in water -ensure plant has enough co2
  3. place light source set distance from beaker, use ruler
  4. allow plant photosynthesize for set time, using stopwatch
  5. photosynthesis occurs,- oxygen collects in capillary tube
  6. experiment finished, use syringe to draw oxygen bubble towards top+ruler to measure length of bubble
  7. repeat experiment+ calculate average-ensure reliable results, whilst keeping variables, temp, controlled
  8. change light intensity by increasing distance between light source+beaker
• how many steps


  8
• independant variable


  light intensity
• dependant variable


  rate of photysnthesis
• control variable


  • temperature
  • species of pondweed
  • conc of co2 (to ensure not limiting factor)
• 1st step

  place pondweed into beaker with water + ensure gas syringe is empty
• 2nd step


  add sodium hydrogen carbonate into water to ensure plant recieves enough co2
• 3rd step


  place light source at specific distance away from beaker eg: 10 cm, using a ruler
• 4th step

  leave pondweed to photysnthesize for set amount of time using stopwatch
• step 5

  as photosynthesis occurs, oxygen released will collect in the capillary tube
• step 6 


  once experiment is finished, use syringe to draw gas bubble in tube towards top + measure length of oxygen bubbles using a ruler
• step 7 


  repeat experiment 3 times+ calculate an average for reliable results whilst keeping variabales eg temp controlled
• step 8

  change light intensity by increasing distance between light source and beaker
• how can you show that the gas released is oxygen

  relight a glowing splint
• how can you change the apparatus to measure temp

  place test tube with pondweed into beaker with a set temp by using a water bath and a themometer
• how can you change apparatus to measure effect of co2

  use different concs of sodium hydrogen carbonate in water