1. An experiment using an aquatic plant to show the production of oxygen due to photosynthesis.
2. The gas is collected over water.
3. There's a separate glass funnel which is fully submerged in water.
4. The oxygen will be collected in a testube which is filled with water. 
5. The testube is attatched to the end of the tube of the funnel. The testube is then lifted vertically therefore we have the wide part of the funnel submerged in water.
6. The aquatic plant is placed under the funnel.
7. As the plant photosynthesizes, the oxygen will travel upwards in the testube and displace the water at the top.
8. With time, the water will be replaced by oxygen gas in the testube.