What is a primary characteristic of free-living organisms?

A primary characteristic of free-living organisms is that they do not depend on one particular organism for food. This means they can obtain nutrients from their surrounding environment rather than relying on a host or another organism to provide sustenance. Free-living organisms can be autotrophic, meaning they produce their own food through processes like photosynthesis or chemosynthesis, or heterotrophic, where they consume organic matter from the environment. This independence from a single source for nutrients helps them thrive in diverse habitats and contributes to their ecological versatility.

The other options, while they may seem plausible, do not accurately describe the fundamental nature of free-living organisms. For instance, while some free-living organisms can adapt to extreme environments, not all can, making that statement overly broad. Additionally, not relying on others for food does not equate to being unable to adapt to extreme environments. The notion of always being pathogenic is also inaccurate, as many free-living organisms are beneficial and play crucial roles in ecosystems without causing disease.