Our Environment

Step 1: Understanding the Concept:
Ecology studies the relationship between living organisms and their environment. The level at which these interactions become a self-sustaining system is considered the functional unit.
Step 2: Detailed Explanation:
An Ecosystem includes all the biotic (living) and abiotic (non-living) components in a particular area interacting as a system. It is considered the basic functional unit because it is the smallest level where energy flow and nutrient cycling are complete.
Step 3: Final Answer:
The correct option is (c).