A closed or semi-closed terrarium is a collection of small plants growing in a transparent, sealed/semi-sealed container. It is a closed environment, and can actually be used to illustrate how an ecosystem works. Inside a terrarium’s walls, many different natural processes may be observed: photosynthesis, respiration, and the water cycle. The water in the terrarium is constantly recycled, passing from liquid form to gas and back again. As the moisture in the air condenses on the glass walls, it returns to the soil and is absorbed by the plants’ roots. Therefore requires very little maintenance in comparison to most terrariums.