One glass bowl
A cup of lukewarm water
A green large leaf plucked from a tree
A small stone
Fill the large glass bowl with the cup of lukewarm water.
Place the green large leaf into the bowl of lukewarm water and put the small stone on top of it, to submerge it.
Place the bowl and the leaf with the small rock in a sunny spot for four hours.
You will notice small bubbles get formed on the leaf.
How does this work?
When the bowl with the leaf is placed under the sunny spot, it begins using the sunlight as part of the photosynthesis process (where leaves convert sunlight to energy).
As a leaf creates that energy, it gets rid of the extra oxygen that is produced during photosynthesis along with water (the release of water from the leaf is called transpiration).
The process of photosynthesis is what allows us to see the bubbles -- as the leaf releases its oxygen while submerged, the oxygen can be seen as bubbles in the water.
Since oxygen is lighter than water, the oxygen bubbles will start rise to the surface.