The biosphere can best be defined as

all Earth's organisms and the nonliving environment with which they interact

Explanation:

The biosphere is the fourth sphere, and consists of the places where life can be found. In other words,it is the layer of the planet Earth where life exists. Biosphere refers to all Earth's organisms and the nonliving environment with which they interact. Life on biosphere depends on the sun. The energy provided by the sun is captured by plants and other photosynthetic organisms through the process of photosynthesis. This energy captured by the plants is used to transform carbon dioxide to organic compounds such as sugars, which is then obtained by other organisms called consumers when they feed on plants.