Which of the following best describes an ecosystem?

• A. Is the same as a community.
• B. Refers only to the genetic makeup of organisms.
• C. Includes both living organisms and the physical environment.
• D. Includes only living organisms.

Answer: (C)

An ecosystem includes both living organisms and the physical environment, plus the interactions between them. This means not only the plants, animals, fungi, and microbes present, but also the air, water, minerals, climate, and other nonliving factors, all connected through energy flow and nutrient cycles. That makes the described option the best match because it captures both the biotic and abiotic parts and their interactions, which define an ecosystem.

Consider how this differs from the other ideas: a community is just the organisms in a place, without the nonliving surroundings. Focusing on genetic makeup centers on genes and variation, not on the living–nonliving interactions or energy flow. Including only living organisms ignores how the environment shapes and supports those organisms.