2.43 describe experiments to investigate the effect of light on net gas exchange from a leaf, using hydrogen-carbonate indicator

Experiment

Hydro-carbonate indicator:

Normal CO2 = Orange

Increased CO2 = Yellow

Decreased CO2 = Purple

1. Take 4 test tubes and put add the same volume of hydro-carbonate indicator to each of them
2. Then take 3 similar sized leaves, roll them up and trap the leaf stem with the bung so they're sitting above the indicator
3. Wrap aluminium around 1, baking paper and leave the 3rd. 
4. Place them in bright light and leave them for an hour. Then check the colour of the indicator

The 4th tube is the control. If the indicator changes in that one there is something wrong with the experiment.