Relationships may be competitive or mutually beneficial. Some species have become so adapted to each other that neither could survive without the other. In the days that follow the initial study of aquatic environments, students observe a variety of events in their classroom aquarium. Elodea grows and forms roots. Snails lay eggs on plants or on sides of the aquarium.
Plants use the energy from light to make sugars from carbon dioxide and water.
This food can be used immediately or stored for later use. Organisms that eat plants break down the plant structures to produce the materials and energy they need to survive. Then they are consumed by other organisms. Over a long time, matter is transferred from one organism to another repeatedly and between organisms and their physical environment. As in all material systems, the total amount of matter remains constant, even though its form and location change.