- Take some twigs of an aquatic plant like Hydrilla in beaker filled with water.
- Invert a funnel over the twigs. Invert a test tube filled with water on the stem of the funnel.
- Keep this set-up in sunlight for sometime.
- Air bubbles (oxygen gas) will be seen coming out from the twigs. If this set-up is kept in the dark, no air bubbles will be seen.
This proves that light is necessary for photosynthesis.
