Apparatus

• Boiling tubes
• Cotton wool
• Aluminium foil
• Gauze
• Rubber bungs
• Hydrogencarbonate indicator
• Leaves

Method

• Measure out 20 cm^3?hydrogencarbonate indicator?into 4 boiling tubes
• Put some cotton wool into each boiling tube
• Label the boiling tubes A-D and set them up as follows:
  • Tube A?- No leaf (control tube)
  • Tube B -?Place a leaf in the tube and leave in the light
  • Tube C?- Place a leaf in the tube and wrap it in?aluminium foil?to block out the light
  • Tube D?- Place a leaf in the tube and wrap it in?gauze?to allow partial light

   

• Put a bung into the top of each tube
• Leave all 4 tubes in the light for 30 minutes

Hydrogencarbonate indicator can be used to study gas exchange in different light conditions

Results

• After 30 minutes, we would expect the following results:
• Tube A?- The control tube should remain an orange/red colour to show that the carbon dioxide is at?atmospheric levels
  • There has been no net movement

   

• Tube B?- This tube was placed in the light with a leaf which is photosynthesizing and respiring
  • Because the rate of photosynthesis is greater than the rate of respiration, the hydrogencarbonate indicator will turn purple as there is?less carbon dioxide?than atmospheric levels

   

• Tube C?- This tube had a leaf inside, but was wrapped in aluminium foil meaning that no sunlight could reach the leaf
  • No light means that this leaf will not photosynthesize but will still be respiring and therefore producing carbon dioxide. The indicator will turn yellow as?carbon dioxide levels increase?above atmospheric levels

   

• Tube D?- This tube had a leaf inside and was wrapped in gauze allowing partial light
  • This means that the rate of photosynthesis equals the rate of respiration so there was no net change in carbon dioxide levels?and the indicator remained orange/red

   

Hydrogencarbonate indicator will change from orange/red to yellow with increasing carbon dioxide or purple with decreasing carbon dioxide

The Effect of Light on Net Gas Exchange in Plants Table

Applying CORMS evaluation to practical work

• When working with practical investigations, remember to consider your CORMS evaluation

CORMS evaluation

• In this investigation, your evaluation should look something like this:
  • Change?- We will change the availability of light for each boiling tube (not wrapped, wrapped in foil, wrapped in gauze)
  • Organisms?- The leaves should be from the same species/age of the plant, they should be approximately the same size
  • Repeat?- We will repeat the investigation several times to ensure our results are reliable
  • Measurement 1?- We will observe the change in the hydrogen carbonate indicator
  • Measurement 2?- after 30 minutes
  • Same?- We will control the volume of hydrogen carbonate indicator, the number of leaves, the temperature of the environment

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