What defines an ecosystem?

An ecosystem is defined as a community of organisms and their physical environment interacting as a system. This definition highlights the integral relationship between living organisms (biotic factors) and their physical surroundings (abiotic factors). In an ecosystem, organisms are not only coexisting but also depend on each other and their environment for survival, which includes factors like water, soil, and climate. This interaction is crucial for the flow of energy and nutrients, and it emphasizes the interdependence of species and their habitats.

Understanding an ecosystem in this way helps to appreciate its complexity, as it encompasses various interactions, including competition, predation, and symbiosis among species, as well as how these living beings influence and are influenced by their non-living environment. Other options, while relevant elements of ecological studies, do not capture this broad and integrative perspective of an ecosystem as well as this answer does.