How is an ecosystem defined?

• A. A single species population in an area.
• B. A group of ecosystems linked by climate.
• C. A biological community and its physical environment.
• D. The soil and water in a habitat.

Answer: (C)

An ecosystem is defined by the living community and the physical environment together, along with the interactions between them. This means all the organisms in a defined area—plants, animals, microbes—and the nonliving parts like air, water, minerals, climate, and soil, and how they affect each other. Energy moves through the system as organisms eat and are eaten, nutrients cycle via processes like decomposition and uptake, and organisms can modify their surroundings, creating feedbacks that shape the whole system. That combination of living and nonliving components and their interconnections is what makes an ecosystem. The other options miss this integrated view: a single species population focuses only on one group, a group of ecosystems tied by climate describes broader biomes rather than a specific system, and the soil and water refer only to abiotic parts, leaving out the organisms and their interactions.