Penn Foster Biology – The Cell Practice Test 2025: Your All-in-One Guide to Master Cell Biology!

The biosphere encompasses the regions of Earth's crust, water, and atmosphere inhabited by living organisms because it includes all ecosystems where life exists. This means it spans multiple layers: the land (terrestrial), bodies of water (aquatic), and the atmosphere where life forms, including plants, animals, fungi, and microorganisms, can be found.

The biosphere is not limited to only areas that are habitable, since it incorporates diverse environments—some of which may be extreme or challenging for life but are still considered part of the biosphere. While aquatic environments are significant, the biosphere itself is not restricted to these regions; it also includes terrestrial areas and the air. Furthermore, the airspace surrounding the planet, which is often regarded in terms of atmospheric study, is not exclusively a habitat for living organisms but rather a component that supports life through processes like respiration and photosynthesis. Thus, the most comprehensive definition captures all elements where life interacts with the Earth.