How would you demonstrate that green plants release oxygen when exposed to light?

1) Some water plants like hydrilla are placed in a beaker containing water and covered by an inverted short-stemmed funnel.

2) On that, invert a tube full of water (level of water in the test tube should be above level of the inverted stem).

3) Place the apparatus under sunlight for few hours and observe the air bubbles collect in the test tube.

4) This gas lights a splinter placed near it due to the presence of oxygen.

Hence, oxygen is released during photosynthesis.

Explanation:

The air bubbles released into the test tube is the result of photosynthesis. As photosynthesis takes place in the plant, it releases oxygen which appears as an air bubble in the water column. The presence confirmed by placing a splinter ahead of the tube containing oxygen. The splinter lights up.