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

1)      Fill four test tubes with hydrogen carbonate indicator

2)      Place in a separate test tube:

·         A plant (test tube A)

·         A snail (Test tube B)

·         A plant and a snail (test tube C)

·         A plant and a snail (test tube D) 

3)      Place Test tubes B and D in a dark place and Test tubes A and C in a place with light

4)      Record the color of the indicator after a period of time

5)      You should find that Test tube B and D were all yellow and Test tube A and C was orange ( the lighter the color the more CO₂ present)

6)      This shows that gas exchange is till occurring in the night, however, photosynthesis does not occur so the carbon dioxide levels when the snail and plant are together at dark are  much higher than during at light because at light the plant takes in the CO₂ to use for photosynthesis