In a closed and self-regulating
system, all the energy can be recycled; materials including carbon,
oxygen, nitrogen, certain minerals, and water can sustain life -
the basic ecological unit is the ecosystem. An ecosystem may be
as small as a tidal pool or a rotting log or as large as an ocean
or a forest.
Each ecosystem has a community of plants, animals and microorganisms
in the environment that supplies them with raw materials for life,
i.e., chemical elements and water. The living organisms are interacting
among themselves and with the environment in which they live
(the climate, altitude, light, water and soil characteristics, and
other physical conditions of the environment).