Concept:An ecosystem is defined by the interactions between living organisms and their non-living environment.
Explanation:An ecosystem includes both biotic (plants, animals, humans) and abiotic (soil, water, air) components.
The key defining feature is the interrelationship between organisms and their surroundings.
This interaction enables energy flow, nutrient cycling, and ecological balance.
Option B correctly captures this essential relationship.
Option A only lists living things, missing abiotic factors.
Option C refers to specific Earth layers, not the full ecosystem.
Option D combines the physical Earth and biosphere but does not emphasize interactions.
Answer:B. interrelationship between organisms and their surroundings