Plants originate, live, and die in communities consisting of plants and a variety of other organisms, large and small. All the living constituents make up the biota (or the biotic component) of the community. The nonliving, physical factors (such as temperature, light, and nutrients) that affect the life of organisms—and determine to a large extent the kinds of organisms present—collectively represent the abiotic factors of the community. The environment is the total of all the biotic and abiotic forces in which an organism or a community of organisms lives.
The biotic components and abiotic portions of the environment are inseparably intertwined and constantly exchange materials; there are inputs (materials or organisms entering) and outputs (materials or organisms leaving) to the community; energy flows one way through the community, nutrients cycle within it. The community functions, therefore, as a dynamic system, an ecosystem. The ecosystem is the most complex level of biological organization.
The ecosystems of the world are distributed in environmentally controlled patterns or biomes, which contain distinctive communities with similar life forms (but not necessarily the same species) across broad geographic areas. Deserts are one kind of terrestrial biome, for example. (Freshwater and marine aquatic ecosystems are not categorized in this manner.)
Ecologists are biological scientists who study the relationships of plants and animals to one another and to their environment. Ecology attempts to understand where, how and, if possible, why organisms live where they do. It searches for theories that can be formulated into ecological principles to better understand the place of organisms in the world ecosystem. Environmental science is an applied science that addresses the problems created by human activities on the functioning of the environment and searches for ways to alleviate the stress created by a burgeoning human population. It draws upon knowledge from all areas in a quest for solutions. Pollution of the environment, a depletion of resources, and an increasing need for food and energy are subjects of major concern to environmental scientists.