All the living and nonliving things interacting in a particular area.

• A. Habitat
• B. Ecosystem
• C. Community
• D. Biosphere

Answer: (B)

Think of an ecosystem as the system formed by living organisms and the physical environment in a defined area, all interacting with each other. In an ecosystem, plants, animals, microbes, air, water, soil, climate, and nutrients form connections through energy flow and matter cycling. For example, in a pond ecosystem, sunlight fuels algae through photosynthesis, algae support herbivores, predators, and decomposers, and nutrients cycle through the water and sediments, all within the temperature and chemical conditions of the pond. This concept captures both the living components and the nonliving surroundings and the interactions among them within a specific area, which is why it matches the description of all living and nonliving things interacting there.

A habitat is the place where an organism lives, focusing on the physical setting rather than the full web of interactions. A community refers to all the populations of living things in an area, but it doesn’t include the abiotic parts of the environment. The biosphere covers Earth as a whole—the global system of all ecosystems and life-supporting processes.