Our most recent science unit is an exploration of ecosystems. We learned there are 4 parts to an ecosystem: animals, plants, decomposers, and non-living things. These bottles contain all four parts including water, soil, grass, fish, snails, gravel, worms, and a water plant. Our bottles have been self sustaining. For two weeks we haven't had to feed the animals or water the plants, and everything is still alive. Take a look: