Question

How will you prove that the water is the source of $O_2$ released during photosynthesis?

Answer 1

Requirements: Test tube, beaker, Hydrilla (aquatic plant) funnel etc.
Method: Take a beaker and place some fresh shoot of submerged water plant (e.g., Hydrilla, Elodea etc.) inside it with their cut ends turned upwards. Now cover it with a funnel and then pour water in such a manner that the stem of the funnel remains under it. Fill up a test tube completely with water and carefully invert it on the stem of the funnel.
Now expose the plant to sunlight. After some time, it will be found that bubbled of gas are given off from the cut ends to the shoots, and these are collected in the test tube by the downward displacement of water. When sufficient gas has been collected, then an ignited match stick is inserted inside the test tube, it is found that the match stick burns very fast. Thus, it is proved that O${}_2$ is evolved during photosynthesis.