gas exchange - flowering plants

• what does hydrogen-carbonate indicator show for changes in CO2 concentration?

  • in air with normal CO2 concentration = orange
  • air with increased CO2 concentration = more CO2 dissolves and become yellow
  • air with decreased CO2 concentration = CO2 will come out of solution and become purple
• how do you carry out the experiment for flowering plants?

  • add same volume of hydrogen-carbonate indicator to four boiling tubes
  • place similar size - healthy looking leaves into three of the tubes and seal with rubber bung - trap leaf stem with bung to stop it falling down into solution
  • 4th tube empty as control
  • wrap one in aluminium foil
  • 2nd tube in gauze
  • place all test tube in bright light - uncovered - lots of light
  • gauze a little and aluminium none
  • leave for an hour and check colour of indicator
• what are the results for the flowering plant experiment?

  • No colour change in control tube
  • aluminium foil = changes to yellow - respiration still takes place but no photosynthesis = increase CO2 concentration
  • gauze = no colour change - little bits of photosynthesis and some respiration = equal amounts of CO2 taken up and produced by the leaf
  • uncovered = changes to purple - some respiration - large amounts of photosynthesis - net uptake of CO2 by leaf - lower CO2 concentration in tube