- Begin with a brainstorming session on how the natural purification of water works.
- Remind students of various self-purification processes in rivers and nature.
- Put the sponge on the top of the empty clear glass. Make a small alcove and pour the muddy water into it. Point out that a sponge can also perform a filtering function.
- Observe what happens and ask students what natural ecosystems could perform the functions of a sponge.
Hint: clear glass with muddy water – pollution in rivers, sponge – wetlands and forests.