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

Explanation

Aim : To prove that oxygen is produced during photosynthesis by Hydrilla funnel experiment.
Apparatus: Beaker with water , test tube , funnel, hydrilla plant, glowing splinter.
Procedure:
1) Arrange the apparatus as shown in the figure.
2) Place some water plant like Hydrilla in a short stemmed funnel and keep it in a beaker.
3) Then pour the water in the beaker.
4) Invert a test - tube full of water over the stem of the funnel.
5) Ensure that the level of water in the beaker is above the level of stem of the inverted funnel.
6) Place the apparatus in the sunlight for at least 8 -9 hours.
Observation :
1) After sometime it is observed that gas bubbles coming from the hydrilla plant. These bubbles are collected at the end of the test tube pushing the water into the beaker.
2) After sufficient gas is collected, test - tube is taken out of the beaker carefully by closing it with thumb.
Test : Test the gas in the test - tube by inserting a glowing incense stick which would burst into flames. This shows the presence of oxygen :
Result : This shows that oxygen is produced during photosynthesis.
Precautions :
1) Funnel should be smaller than the beaker.
2) Care should be taken while removing test tube from the stem of funnel.