Which term refers to all living things in a particular area?

• A. Population
• B. Community
• C. Organ System
• D. Ecosystem

Answer: (D)

A key idea here is how ecologists categorize the different levels of biological organization. A population is just all individuals of one species in an area. A community expands that to all populations of different species living in the same area. An ecosystem goes a step further by including not only the living organisms but also the physical environment—air, water, minerals, climate—and how energy and nutrients move and cycle through that system. So, when the question asks for the term that describes all living things in a particular area as part of a larger, interacting system, the ecosystem best fits because it encompasses the living world and its connections to the surrounding environment and processes. The other terms don’t capture that broader interactive context: a population concerns a single species, a community concerns multiple species without the abiotic context, and an organ system is a structure within an individual organism.